Guest Episode
October 24, 2021

Dr. Samer Hattar: Timing Light, Food, & Exercise for Better Sleep, Energy & Mood

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In this episode, Dr. Huberman hosts Dr. Samer Hattar, Chief of the Section on Light and Circadian Rhythms at the National Institute of Mental Health. Dr. Hattar is a world-renowned expert on how viewing light at particular times adjusts our mood, ability to learn, stress and hormone levels, appetite, and mental health. They discuss how to determine and use your individual light sensitivity to determine the optimal sleep-wake cycle for you. They also discuss how to combine your light viewing and waking time with the timing of your food intake and exercise in order to maximize mental and physical functioning.

Dr. Hattar is credited with co-discovering the neurons in the eye that set our circadian clocks and regulate mood and appetite. He explains why even a small shift in daylight savings leads to outsized effects on our biking because of the way that our cells and circadian clocks integrate across many days. And he offers precise tools to rapidly adjust to jetlag, shift work, and reset your clock after a late night of work or socializing. This episode is filled with cutting-edge data on the biological mechanisms of human physiology and practical tools for people of all ages.

Dr. Sammer Hattar

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About this Guest

Dr. Samer Hattar

  • 00:00:00 Introducing Dr. Samer Hattar, Ph.D.
  • 00:02:17 Sponsors: ROKA, InsideTracker, Magic Spoon
  • 00:06:15 Light, Circadian (24 hour) & Circannual (365 day) “Photoentrainment”
  • 00:14:30 Neurons in Our Eyes That Set Our Body Clocks: Similar to Frog Skin
  • 00:18:55 What Blind People See
  • 00:20:15 When, How & How Long to View Light for Optimal Sleep & Wakefulness
  • 00:30:20 Sunlight Simulators, Afternoon Light Viewing, Naps
  • 00:33:48 Are You Jetlagged at Home? Chronotypes & Why Early Risers Succeed
  • 00:38:33 How to Decide Your Best Sleep-Wake Schedule; Minimal Light Test
  • 00:42:16 Viewing Light in Middle of Day: Mood & “Light Hunger”
  • 00:44:55 Evening Sunlight; Blueblocker Warning
  • 00:48:57 Blue Light Is Not the Issue; Samer’s Cave; Complete Darkness
  • 00:53:58 Screens at Night
  • 00:56:03 Dangers of Bright Light Between 10 pm and 4 am: Mood & Learning
  • 01:01:05 The Tripartite Model: Circadian, Sleep Drive, Feeding Schedules
  • 01:05:05 Using Light to Enhance Your Mood; & The Hattar-Hernandez Nucleus
  • 01:07:19 Why Do We Sleep?
  • 01:08:17 Effects of Light on Appetite; Regular Light & Meal Times
  • 01:18:08 Samer’s Experience with Adjusting Meal Timing
  • 01:22:51 Using Light to Align Sleep, Mood, Feeding, Exercise & Cognition
  • 01:30:15 Age-Related Changes in Timing of Mental & Physical Vigor
  • 01:31:44 “Chrono-Attraction” in Relationships; Social-Rhythms
  • 01:33:40 Re-setting Our Clock Schedule; Screen Devices Revisited
  • 01:37:50 How Samer Got into the Study of Light
  • 01:39:33 Clock Gene mRNAs & More Accurate Biomarkers
  • 01:41:08 Light as Medicine
  • 01:42:48 ADHD (Attention-Deficit Hyperactivity Disorder)
  • 01:43:35 How to Beat Jetlag: Light, Temperature, Eating
  • 01:50:44 Vigor: The Consequence of Proper Timing
  • 01:52:15 Waking in the Middle of the Night: When Your Nightly Sleep Becomes a Nap
  • 01:54:10 Melatonin, Pineal Calcification
  • 01:55:25 Our Seasonal Rhythms: Mood, Depression, Lethargy & Reproduction
  • 01:59:08 Daylight Savings: Much Worse Than It Might Seem
  • 02:05:27 Eye Color & Sensitivity to Light, Bipolar Disorder
  • 02:09:28 Spicy Food, Genetic Variations in Sensory Sensitivity
  • 02:10:52 Synthesizing This Information, Samer on Twitter, Instagram
  • 02:13:00 Conclusions, Ways To Support the Huberman Lab Podcast & Research

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Andrew Huberman:

Welcome to the Huberman Lab podcast, where we discuss science and science-based tools for everyday life.

Andrew Huberman:

I'm Andrew Huberman and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. Today, I have the pleasure of introducing Dr. Samer Hattar as my guest on the Huberman Lab podcast. Dr. Hattar is the Chief of the Section on Light and Circadian Rhythms at the National Institute of Mental Health in Bethesda, Maryland. Dr. Hattar has many important discoveries to his name. He was one of a handful of groups that discovered the light-sensing neurons in the eye that set the circadian clock. This is a fundamental discovery made in the early 2000s that has led to an enormous number of additional discoveries on how light regulates our sleep, our immune system, our mood, mental health, metabolism, feeding and many other important processes. If ever there was somebody who understands how all of these processes interact and can inform best practices for our daily behaviors, it's Dr. Hattar.

Andrew Huberman:

During our discussion today, Dr. Hattar answers questions that are absolutely essential for us to know about our health and well-being. For instance, how to align our sleep schedule with our activity schedule, such as exercise, and how to align light activity and exercise with our feeding rhythms. He presents a new model of how light activity and feeding rhythms converge to support optimal health, and when those are not aligned correctly, how our mental and physical health can suffer.

Andrew Huberman:

It's a discussion that is rich with scientific mechanism, made clearly, of course, so everybody can understand, as well as specific protocols to deal with shifts in day length, shifts in activity, and in order to optimize sleep, metabolism and well-being of various kinds. I learned so much from Samer, as I always do. He is an absolute wealth of knowledge on all things related to light and circadian rhythms, physiology, and neuroscience. I don't think you'll find anyone else as knowledgeable about these topics as Samer, and so I'm delighted that he joined us here on the podcast to share this information.

Andrew Huberman:

Before we begin, I'd like to emphasize that this podcast is separate from my teaching and research roles at Stanford. It is however part of my desire and effort to bring zero-cost-to-consumer information about science and science-related tools to the general public. In keeping with that theme, I'd like to thank the sponsors of today's podcast. And now my conversation with Dr. Samer Hattar. Samer, thanks for sitting down with me.

Samer Hattar:

My pleasure.

Andrew Huberman:

Yeah, we go way back. So, you are best known in scientific circles for your work on how light impacts mood, learning, feeding, hunger, sleep, and these sorts of topics. So just to kick the ball out onto the field, so to speak, how does light impact the way we feel? So when I get up in the morning, I have the opportunity to interact with light in certain ways or to avoid light in certain ways. I have the opportunity to interact with sunlight or with artificial light. Maybe you could just wade us into what the relationship is between light and these things like mood and hunger, et cetera.

Samer Hattar:

Sure. So I mean you do appreciate the effect of light for vision. So when you wake up in a beautiful area, beautiful ocean, light is essential. The sunrise, the sunset, blue sky, beautiful mountains. So that's your conscious perception of light. But light has a completely different aspect that is independent of conscious vision or image-forming functions. And that's how it regulates many important functions in your body. I think the best that is well-studied and well-known is your circadian clock. And the word "circadian" comes from the word "circa," which is approximate, and "dian" is day, so it's an approximate day. Why is it an approximate day? Because if I put you or any other human being who have a normal circadian clock in a constant conditions with no information about feeding time, about sleep time, about what time it is outside, you still have a daily rhythm, but it's not exactly 24 hours. So it will shift out of the solar day because it's not exactly 24 hours, and hence the name circadian.

Andrew Huberman:

So just to ask a quick question about that, when you say you have this, about, 24-hour rhythm, how does that rhythm show up in the tissues of our body?

Samer Hattar:

Great. Great question. So, it shows up at every level that we know we studied, it shows up at the level of the cell, it shows up at the level of the tissue, and it shows up at your behavior. The most obvious for you is your sleep-wake cycle. You sleep, and you're awake and sleep at the 24-hour rhythms. And if you measure the sleep-wake cycle of humans who are maintaining constant conditions, you will see that the period length of the sleep rhythm on average is more than 24 hours and humans is 24.2 hours. So you'll be drifting 0.2 hours every day out of the solar day if you don't get the sunlight. So the sunlight adjusts that approximate data on exact days, so now your behavior is adjusted to the light dark environment or the solar day.

Andrew Huberman:

Okay. So if I understand correctly, if I were to go into a cave or I were to be in constant light, and I didn't close my eyes in constant light, that I would still sleep in one coherent bout, and I would still be awake for more or less one coherent bout, maybe a nap, but the total duration of my day, so to speak, would be a little bit longer than 24 hours?

Samer Hattar:

Perfect.

Andrew Huberman:

But if I'm in a condition like most people are where the sun goes up and the sun goes down, and I have some understanding of that sunrise and sunset, then-

Samer Hattar:

You don't have to have the understanding, you don't have to have conscious understanding. You have the detection. So circadian "photoentrainment" is the word we use in training the circadian clock to the photic environment, is completely subconscious. You're not aware of it. It's not like vision or image forming where you actually know what you're looking at. So, it's all hypothalamic. It's part of the brain that is not consciously driven, so you actually do not know when it happens or when it doesn't happen. And that what we'll get into when I tell you why light affects your mood and why sometimes people don't know how to deal with light to improve their mood, for example.

Andrew Huberman:

Okay. So this is a subconscious vision?

Samer Hattar:

Yes.

Andrew Huberman:

Okay. Before you tell us about how light impacts mood, I'm curious, what is the relevance of adjusting this clock from little bit longer than 24 hours to 24 hours? I mean it seems like a small difference, 24 hours and 40 minutes or 24 hours, what's the relevance? I mean, why should we care about that short difference?

Samer Hattar:

So let's do the math. If you shift out 0.2 hours a day, in five days, you're shifting out one hour. So you're literally one hour off in your social behavior in five days. In 10 days, you're two hours off. And if you're an organism that is living in the wild, shifting out of the right phase of the cycle, you could either miss food or you could become food. So it's really essential for survival. I think it's one of the strongest aspect of survival for animals to have the anticipation and the adjustment to the solar cycle.

Andrew Huberman:

And for humans as well. When you say animals, I'm assuming that applies to us.

Samer Hattar:

Absolutely, yeah.

Andrew Huberman:

I see. So even though it's just a short bit longer than 24, if that accumulates over days, then you could find yourself very much out of phase with the rest of your species, essentially.

Samer Hattar:

Yeah. So let's say it's 0.2 hours, so in five days, it's one hour. In 25 days, it could be five or six hours. You could be in New York, and you're feeling as if you traveled from New York to London. So you would be having jet lag in New York even though you didn't do a jet lag travel. So it's very important for the adjustment. And if we have time, maybe we could talk about why this is important for seasonality, because also it allows animals to anticipate the change in season. And the more you are high in the north or the south, the more that these weather changes occur very harshly, and you have to be ready for them. And that happens in us as well.

Andrew Huberman:

All right. Well we will definitely get into seasonality. So we've got this subconscious vision that aligns us with the turn of the earth. How does that work? What is the machinery that allows that to happen, and how does that machinery work?

Samer Hattar:

Yeah, so we knew that in mammals, including us — we are mammals, humans — that the eyes are required for this function. So, if humans are born without eyes or the optic nerves are damaged, humans are not able to adjust to the solar cycle. So we know that the eyes are required. And since we thought we knew about the eyes a lot before 2000, we thought that-

Andrew Huberman:

Well, you said before the year 2000?

Samer Hattar:

Before the year 2000, yes. We thought it's these photoreceptors in your retina that allow you to see. So in the human retinas, there are two types of photoreceptors. They are called rods and cones because of their shapes. And these rods and cones simply take the photon energy, which light is made of, and they change it in a way to an electrical signal that allow us to build the image of the environment in our cortices.

Andrew Huberman:

Subconsciously?

Samer Hattar:

Consciously, in this situation because it's vision, right? It's image-forming vision, it's a visual cortex and association cortices which allow you to build conscious perception of the environment. However, people have found, including me, with the work of David Berson and Ignacio Provencio, that there is a subset of ganglion cells. The ganglion cells are the cells that leave the retina, their axon, leave the retina and project to the brain. So these [inaudible 00:10:10] to only really a rod and cone information from the light environment to the brain. We found that a small subset of these ganglion cells are themselves photoreceptors that were completely missed in the retina. And these are the photoreceptors that relay light environment subconsciously to the areas in the brain that have and house the circadian clock or the circadian pacemaker, which adjust all the clocks in our bodies to the central brain clock that allows them to entrain to the 24-hour light dark cycle.

Andrew Huberman:

Incredible. As I recall, because I was a graduate student at the time, in the year 2000, there was this landmark discovery made by you, Iggy Provencio, David Berson and others, that these cells exist that can communicate day and night information to the brain in this very small subset of cells. Since then, I've heard, but maybe you can confirm or refute, that this system that connects the eyes to the rest of the brain is actually the most ancient form of vision, that this is probably the form of vision that some early version of human beings had before they had pattern vision, before they could see colors and shapes and motion, and all that, and that the same cells that perform this role are actually similar to insect eyes. I think I heard David Berson say once that we actually have a little bit of the fly eye in our eye. What's he talking about?

Samer Hattar:

Yeah. So it's really interesting actually because these same ipRGCs, we discovered they contribute a little bit to image formation, and now, work from Tiffany Schmidt specifically have proven that they do contribute to image-forming functions, but they contribute to very limited aspect of image formation. So it fits your hypothesis that these are an ancient photoreceptors. The other thing that adds to that hypothesis is that they're expressed in cells that don't have any modification that make them look like photoreceptors. So the photoreceptors that I told you about that are important for vision, image formation, they have very specialized structures that allow them to pack these structures with photo pigments, these are the photo-detecting proteins, so they could detect a high sensitivity of photons that pass through them. These new photoreceptors don't have these specialized structures, so they just really need a lot of light. At the time, we thought they need a lot of light to be activated.

Samer Hattar:

So that's why we think they are ancient, and that's why I think they adjust to ancient functions that are as important as regulating your body circadian clock to the solar environment, to solar day or to the light dark cycle.

Andrew Huberman:

So you mentioned ipRGCs, intrinsically photosensitive. So these are cells that connect the eye of the brain that behave like photoreceptors, essentially. And then you mentioned melanopsin, which is the actual pigment that converts the light into the electrical signal, more or less. And my understanding is that melanopsin was identified first in frog melanophore. So does that mean that we have little pieces of frog skin in our eyes?

Samer Hattar:

So honestly, David Berson say you have a fly in your eye because it sounds better. The more accurate I think is that you have a frog skin in your eye. It's not as catchy, but really, melanopsin, really the name melanopsin is from melanocyte oxin. So it's melanopsin because it was found in the frog melanocytes. The frogs can change their color depending on light, and melanopsin drives this response. So when Ignacio Prevencio first discovered these oxins in frogs, luckily, he was smart enough to see if they're expressed in the frog eye. They were expressed in the frog eye and it what appears to be retinal ganglion cells, which I told you the one that connect the eye to the brain. He had the insight to go and see if they're expressed in the monkey eye, and he found that they are also expressed in what appears to be retinal ganglion cells. And really that what opened the field wide open.

Samer Hattar:

Then, David Berson did the seminal experiment where he went to the brain where the central oscillator, the oscillator that drives circadian rhythm in the brain, called the suprachiasmatic nucleus, that has been known for many years to receive retinal input. And he labeled the cells that project there. And then, he found that even if you destroy rods and cones, you could get light responses from these cells. So you could imagine, he nearly fainted when he saw that these cells can respond independent completely in the absence of rod and cone input.

Andrew Huberman:

I'll never forget reading those papers in 2000, 2001; I was at the meeting in D.C. when Ignacio — Iggy, we call him Iggy — showed this image of basically what is frog melanophores in the human eye. And everyone was like, "Oh my goodness, this is the thing." And I want to get into how light actually can control circadian rhythms in a moment.

Samer Hattar:

Absolutely.

Andrew Huberman:

But I think it's worth mentioning now that people who are pattern vision blind, so people who cannot see, and no conscious vision, but have eyes, many of them still have these cells, these melanopsin intrinsically photosensitive cells and can essentially match, or entrain as we say, onto the light dark cycle.

Samer Hattar:

In fact, they possibly have no problems in circadian photoentrainment. They'll have enormous sleep-wake cycle.

Andrew Huberman:

But they're totally blind?

Samer Hattar:

But they are totally image blind. And what's really interesting is that, and this story I heard from Chuck Sisler, so I'll give him credit, that some of these people who are image blind, usually they get dry eyes and they give them a lot of pain. And doctors used to think, "Oh, since they are image blind and they're getting dry eye, why don't you just remove their eyes? They're not using them anymore." And the minute they would remove their eyes, they start having cyclical sleep problems, indicating that now they are not entraining to the light dark cycle and are having cyclical jet lags when their clock shifts through the light dark cycle.

Andrew Huberman:

That's really interesting and I hear from a number of blind people in my various aspects of my job, and a lot of them have issues with sleep, I think in part because they don't realize that they too need to see light at particular times of day or night in order to match their schedule.

Samer Hattar:

Absolutely.

Andrew Huberman:

Well, I think that's a perfect segue for us to talk about how light and viewing light can impact our sleep-wake rhythms, and then we will move into some of the other ways in which light can impact other forms of bodily function.

Samer Hattar:

I love the way you set it up because one of the most interesting and difficult aspect of trying to educate people about light effect on subconscious vision is that it's subconscious. So we're all aware of what we think is intensity because we see the room. But if you talk to people who know how to take photographs, and stuff like that, they know that the intensity varies greatly. But our system, because we have to see the same way in very bright conditions and very dim conditions, we're not very good at estimating intensity consciously. So when you try to tell people about intensity, you really struggle because they think they know intensities, but they really don't.

Andrew Huberman:

You mean light intensity?

Samer Hattar:

Light intensity. So that the cones themself have an incredible ability to adapt to different light conditions. So you can see at all different conditions, otherwise, it'll be a disaster. If you don't change the setting on your camera and you go from inside the room to the outside, it becomes completely white. You don't see anything. So if your cones don't adapt to the environment, then you're not going to be able to see in this room and on the beach. Right?

Samer Hattar:

But the problem is your ipRGCs, the cells that we talked about, they measure intensity pretty well. They really know what intensity is. They have a very good linear measurement of intensity. They don't adapt actually that much, to be honest. So that tells you that subconsciously, the system is used to measuring light intensity in a natural environment, because when you are in a natural environment, you don't have industrialized lighting, then your system is functioning very well. But now, when we change these environments, we could really mess up ourselves. So you have to teach people how to understand intensity, and that's something that you have to explain to people, and I think I love to do it myself. I do it in what is called the lowest amount of light required to allow you to see comfortably. So you have to do this as a fun experiment.

Andrew Huberman:

So explain to me how this goes, and maybe we could break it up ... the day into three or four parts. So let's say, assuming that most people wake up in the morning as opposed to — night shift workers, et cetera, we could talk about later — but you wake up in the morning, so let's divide the day into quarters. What is the proper way to interact with light in the first part of the day?

Samer Hattar:

So I honestly think the easiest thing is waking up. Get as much light as you can

Andrew Huberman:

To your eyes?

Samer Hattar:

Yeah, it's really nice. Your system is primed. If you're entrained, it's primed to get light, the sun should be out. Most animals in the world, they actually seem to track the sun. The sun has a huge influence on life on earth. Life on earth is because of sun. So, that's easy. In the morning when you wake up, you need light.

Andrew Huberman:

Okay, so what is the behavioral practice that you recommend? Let's say somebody is in a condition where there's a lot of cloud cover. Is it important to get outside?

Samer Hattar:

So I have to tell you, the cloudiest day is going to be much more brighter than your room. You could ask any photographer — a cloudy day, unless it's really dark clouds. Usually cloudy days have much more bright outside than inside your room, even when you have good lighting inside the room. So I think in the outside is usually, even when it's cloudy, you're going to get enough intensity to help you adjust your cycle to the day-night cycle.

Andrew Huberman:

So these are general rules of thumb, but how long do you recommend people go outside?

Samer Hattar:

If you do it daily, because you remember, this thing is going to happen on a daily manner. So let's say 15 minutes-

Andrew Huberman:

So the clock is tracking it on a regular basis?

Samer Hattar:

Absolutely. It's spot-on counting, it's tracking. I would say 15 minutes. If you don't do it daily, you may want to increase it. And we'll talk about when you travel what you could do. But yeah, 15 minutes should be fun. You do it more, it doesn't hurt.

Andrew Huberman:

My understanding is that through a window, it dramatically decreases the amount of light energy coming down.

Samer Hattar:

It depends of how thick the windows are and how dark they are. But it's also nice to go outside and to feel the season.

Andrew Huberman:

Sunglasses off?

Samer Hattar:

I don't use sunglasses.

Andrew Huberman:

But you have your Jordanian pigment.

Samer Hattar:

That's right.

Andrew Huberman:

Whereas my eyes are very sensitive, right?

Samer Hattar:

Yeah. No, but I personally, if I'm in the shade or if it's not incredibly bright, I try to, especially in the morning, but I'm also an early person, so we have to differentiate between early and-

Andrew Huberman:

What time do you wake up?

Samer Hattar:

I wake up at 4:30 in the morning.

Andrew Huberman:

But the sun isn't ... Okay.

Samer Hattar:

It's not out yet.

Andrew Huberman:

So what do you? You turn on artificial lights?

Samer Hattar:

I usually don't turn on artificial light because I know the sun is going to come up eventually, but that's why I don't like the change in the timing that they do.

Andrew Huberman:

Wait, but what do you do between 4:30 a.m. and 7:00 a.m.?

Samer Hattar:

I look at my computer and iPhone.

Andrew Huberman:

Oh, I see. Okay.

Samer Hattar:

So possibly, I get enough light. But in reality, I mean, as long as you let your body get the morning sunlight, which I think is really ... there's no evidence, but to me, if you look at all animals, plants ... This morning, sunlight seems to be very important. And we don't have experiments to show it, but I have a gut feeling that it has a huge impact on humans.

Andrew Huberman:

Well, Jamie Zeitzer's lab at the Stanford Sleep Lab has shown that these early-morning light flashes can adjust the total amount of sleep that one will get, makes it easier to get into sleep.

Samer Hattar:

Absolutely. Absolutely.

Andrew Huberman:

Okay.

Samer Hattar:

And can write also, did this beautiful camping experiments that showed-

Andrew Huberman:

Right, maybe you could describe those because those are beautiful experiments.

Samer Hattar:

Oh, yeah. They are beautiful experiments. He took these college students that had a late onset of sleep and late waking time, and then he said, "Let's go camping and just don't use any artificial light, and you could go sleep as late or as early as you want, and wake up as late, as early." And he found a huge shift in their sleep pattern just by exposing them to the light dark cycle.

Andrew Huberman:

And it lasted.

Samer Hattar:

And it lasted.

Andrew Huberman:

Even after they came back-

Samer Hattar:

Exactly.

Andrew Huberman:

... I think it was two days of camping reset the circadian clock.

Samer Hattar:

Seven days, but it lasted, yeah. It's pretty amazing. Yeah. It's really incredible.

Andrew Huberman:

Okay, so get bright light of some sort early in the day. Ideally sunlight, even on a cloudy day. It's going to be absolutely brighter than indoor light. Okay.

Samer Hattar:

So that's easy. And the other thing that I would like to mention to people, if you think it's very dim outside, let's say it's very cloudy, stay longer. So remember, intensity is only one component. Duration is also important, because remember that the circadian system is not like the image system. In the image system, you have to change every second because you're looking at different objects, you have to change your perception. But for the circadian system, it's trying to figure out where am I in the day-night cycle. So the more you give them the information, the better you are. So if it's very bright, you don't need a lot because it's clearly going to make you fire like crazy. But if it's not bright, stay longer, stay for one hour, have your coffee outside, or something like that. It's just going to help.

Andrew Huberman:

I think you said something extremely important, which is that this circadian system is trying to figure out when you are in time, not where you are in space.

Samer Hattar:

Sorry, I said where you are in time, I meant when you are.

Andrew Huberman:

Oh no, no, I wasn't correcting you. I just meant that I think, fundamentally, that's the incredible thing about this system, that you have this clock, this 24-clock in your brain, but it needs to be synchronized to the outside. So, could we go a little deeper into this circadian-setting behavior and come up with some general rules of thumb. So let's say it's a very bright day, extremely bright, no clouds, the sun's out. You said 10 minutes, 15 minutes.

Samer Hattar:

And I'll tell you, if you're sensitive, you don't even have to go in the sun. You could be in the shade. There's going to be so many photons out there in the shade, it's going to be perfect. You don't even have to see the sun, you don't have to have the sun. It's great for vitamin D, that's a different story. You could do this for your skin and protect your skin. That's not my area of expertise. But for that effect on the circadian system, as long as you're outside in the shade, and it's sunny day, 10 to 15 minutes should be ample amount.

Andrew Huberman:

Okay. And then let's say it's kind of overcast, it's not particularly bright, or there's solid cloud cover, but obviously, the sun is out, but it's not as bright. How long do you think it would take to set the clock?

Samer Hattar:

Ten to 15 should be sufficient. Stay for half an hour, stay for 45 minutes. If it's very dark cloud, stay for longer.

Andrew Huberman:

And if for some reason one finds themselves very far north and it's very, very dense cloud cover, how long and at what point should somebody consider using an artificial light source to mimic the sunlight?

Samer Hattar:

Yeah. Honestly, this is where we don't have a lot of information still, because this is where we're going to discuss this maybe in more detail, that if you put humans in artificial conditions, the circadian system is very sensitive to light. But in reality, in the real environment, light also is affecting other aspects that are independent of the setting of the circadian pacemaker, and these which we call the direct effect of light on mood, for example. So that is very hard to figure out what intensity you need to use, and we haven't done enough experience because the system has been discovered just recently. But I would say, if you use bright light in the morning, and I mean it's hard for me to give numbers, it can get complicated. I mean honestly, if you are that far north and you're in the winter and you want to get ... make sure you ... use these light boxes, I would suggest that personally. But that is-

Andrew Huberman:

I use, it's actually not designed for circadian setting, but I have a 930 lux LightPad that I bought. They're very affordable compared to the dawn-simulating lights, which are quite expensive, frankly. And I put it there. And so, just basically when I wake up in the morning, I use that until the sun comes out, and then I make sure once the sun is out, I go outside. But I keep that thing on all day, and I don't know if that's good or bad. Is it good or bad?

Samer Hattar:

Honestly, I don't think being exposed to bright light in the day is going to ever be bad because really, if you're outside in the day and unless, the worst that's going to happen, if the temperature is very high, your body's going to say, "Don't dehydrate," and go to sleep. So you could tell actually sometimes when it's very hot, the more you get exposed to bright light, the sleepier you feel in the afternoon, which is counterintuitive.

Andrew Huberman:

But that's to protect us, you think against dehydration?

Samer Hattar:

I think if you think about the human evolution from near the equator between noon and a certain time in the afternoon, it would have been very hard for you to maintain physiological homeostatic function being active at this very high-temperature time, so I think napping was a way, that's why I think it has a major function; napping was a way to somehow take you away from that dangerous zone. And maybe that's why people in the north, they say in the winter, "We can't wake up in the morning," because they don't have this long light, so they sleep it more at night. But in the summer, they say we feel like we can't go to sleep, we have to put all these dark curtains.

Samer Hattar:

So I think venturing that much up north came up with a problem because evolution was used to a certain light environment; that was completely changed with a human. With other animals, I think, that lived there longer, they have come up with very interesting adaptation of actually measuring even very small changes in the light intensity that still occur. And even if you're near the poles, even though it's always light, but there is a change in the light intensity across the day and night cycle. So your system, if it's linear, and remember I told you that ipRGCs are incredibly linear, can still measure, "Oh, this is lower light than higher light," if the organism has the ability to do that.

Andrew Huberman:

I see. It's interesting. I've spent so much time learning from you, fortunately, about these cells, and yet I never really appreciate it until now how on the one hand, they are tracking the amount of light to understand when we are in time relative to the 24-hour cycle, but also that you keep mentioning this linear measurement of intensity, that they really are trying to figure out when we are in time by measuring the intensity of light. And of course, the sun is the most intense source of light available to us. So I think we have nailed down that first part of the day.

Samer Hattar:

Exactly.

Andrew Huberman:

Basically, it's get 10 to 30 minutes, depending on how bright it is, and try and do that as often as possible to give the system a regulation.

Samer Hattar:

Daily is the best. This system is really about, and you'll see that even for the effect on depression, it's about multiple days. So you don't have to worry if you missed it one day, stay longer if you want, but if you are in a hurry and you want to do other stuff, that's a great recommendation.

Andrew Huberman:

So you might want to compensate with some extra time if you missed a day or two. And this is why, I've heard you say before, it's entirely possible to get severely jet lagged without traveling-

Samer Hattar:

Absolutely.

Andrew Huberman:

... simply by staying in, being on your phone too much, not getting the sunlight.

Samer Hattar:

And you saw this during the pandemic, a lot of people mentioned that their sleep-wake cycle suffered a lot because if you're not going out, and if you're staying at home, and you don't have big windows, and you're waking up late, and then you're using very bright light till late at night, your body's going to shift. And now, your day is going to start instead of, really, when the sun comes up, let's say at six o'clock in the morning, your day is going to start at 11 o'clock in the morning. That's what your body's going to think is the beginning of the day. So then you're not going to be able to sleep at 10 o'clock at night, because now that's really, for your body, it's completely different timing. And you could see this happen during the pandemic at a very high scale. People got delayed in their sleep-wake cycle a lot.

Andrew Huberman:

And there is this idea of chronotypes, that we all each intrinsically have a best rhythm of either being a morning person, you called yourself an early person, or a night owl, or more of a kind of standard to bed around 10:30 up around 7:00 type thing. And I think there are now good data, correct me if I'm wrong, from the National Institutes of Mental Health and elsewhere showing that the more we deviate from that intrinsic rhythm, the more mental health issues and physical health issues start to crop up.

Samer Hattar:

So there is great data on this and there is couple of things that complicate this. The first is the people who usually are late, they tell you that the society doesn't accommodate.

Andrew Huberman:

By late, what do you mean? People that wake up late and go to sleep late?

Samer Hattar:

Go to sleep late and wake up late, they have an overwhelmingly higher level of depression and failures. Clearly, I mean the reason the people say "Sleep early, wake up early are better" because human notice that people who go to sleep early and wake up early, they do better in life. They notice that.

Andrew Huberman:

They just perform better.

Samer Hattar:

They perform. But the question is, is that intrinsic to the system or is that society? Because society start things usually early or late. That's a hard question to ask.

Andrew Huberman:

We discriminate against late risers.

Samer Hattar:

In a way, we discriminate, right? But the other explanation is can rise experiment. These late riser, if they were truly chronotypically late, why would they shift so easily when you put them in the ... If you were really chronotypically late and there is a phase relation between the light dark environment and your circadian clock, then doing this camping experiment should not have caused much changes because it's not that light is going to affect you in a certain way, is that this is the relationship that your body decided, that I'm a late sleeper, late waking. So honestly, I'm still ...

Samer Hattar:

... late waking. So, honestly, I'm still unable to figure out how much of this late waking up is controlled by the light environment and how much is intrinsic. I'm sure there are differences, but are they as big as we see in the environment? Because you have people that go out to sleep at 7:00 p.m. and wake up at 1:00 a.m. These are clearly advanced phase.

PART 1 OF 4 ENDS [00:33:04]

Andrew Huberman:

So, people that go to sleep at 7:00 p.m. and wake up at 1:00 a.m.?

Samer Hattar:

Yeah.

Andrew Huberman:

And feel good doing that?

Samer Hattar:

I'm not so sure they feel good, but a lot of the time you talk to people, they say they are high achievers. But they suffer, because they go to 7:00 p.m. wake up advanced phase sleep syndrome, they call it a syndrome. But then you have people who would not be able to sleep until 5:00 a.m. and not be able to wake up until 3:00 p.m., right? And I'm not so sure that the circadian system is that variable in the human population. I mean, clearly there are maybe some genetic factors that make a small percentage of everything with a bell shape. But I think most of the time, the light environment may play a role. And once, as we've talked about, this is a long-term effect of light. Once you get into a rhythm, and I don't mean it as a pun. In reality, once you get into a rhythm, it's hard to break out of that rhythm because if you start sleeping late and waking up late, you're not getting the morning sunlight.

Andrew Huberman:

Right.

Samer Hattar:

And so you're just going to be late. And if you're like me waking up early, you're getting the morning sunlight, you're getting what Zeitzer said ... I said his last name wrong. The one in Stanford who did the ...

Andrew Huberman:

Oh, Jamie Zeitzer.

Samer Hattar:

Zeitzer.

Andrew Huberman:

Yeah.

Samer Hattar:

Yeah.

Andrew Huberman:

He actually worked for Czeisler.

Samer Hattar:

Czeisler. Yeah it's confusing.

Andrew Huberman:

There are a lot of Zs and I's in their names.

Samer Hattar:

Yeah.

Andrew Huberman:

Both phenomenal scientists.

Samer Hattar:

Yeah.

Andrew Huberman:

What it seems to me is the case, is that the only way to really know if you're meant to be an early bird, as they call it, an early person or a late person or somewhere in between, is to get morning sunlight and figure out whether or not that makes you feel better.

Samer Hattar:

And to understand, to be educated about how to measure intensity, how to measure, I put it between connotation. Because you either get a measuring device, but you cannot depend on your eye to measure intensity.

Andrew Huberman:

Okay. So, how do we do that? Because you keep coming back to this ... Sorry, that tells me that it's important.

Samer Hattar:

It's very important.

Andrew Huberman:

So, obviously, there are free apps like Light Meter, where you can walk around and hold the button down and see how many lux are in the environment.

Samer Hattar:

These are complicated because you have to point them to specific regions.

Andrew Huberman:

So, how do people start to develop an intuitive sense of the measurement of intensity?

Samer Hattar:

Yeah. I think at one point I posted on Instagram how I keep my nighttime at home, and I found out that my night vision is very strong. So, I found out that especially in the winter, I only need candle lights. So, I literally use these tea lights and I put 15 or 20 of them.

Andrew Huberman:

How romantic.

Samer Hattar:

And it's so nice. I could see, it clearly doesn't affect my circadian system.

Andrew Huberman:

You and your cats.

Samer Hattar:

And my wife.

Andrew Huberman:

And your wife, of course.

Samer Hattar:

It's just great. It's just great, right? But I don't expect people to have the same night vision as me. So, I mean I just tell people do the experiment. So, if you put three or four lights in your room, switch two, sit for 15 minutes, switch two off. Switch two off, let's say you're using five, and see after 15 minutes, you will not recognize you switch these two off. My gut feeling is that most people would need at least 10 times less light than they use at night to see. The problem people use it, because most of the time they didn't see the morning sunlight. They are actually hungry for light without their knowledge. So, they come switch all these lights on, but at the wrong time because they woke up late.

Andrew Huberman:

Okay. Now I understand. So, this morning light viewing goes way beyond setting your clock.

Samer Hattar:

Absolutely.

Andrew Huberman:

It's also a way to determine how little light you need later in the day.

Samer Hattar:

Exactly.

Andrew Huberman:

And we're going to talk about this in a moment, but how little light you get later in the day is a very strong determinant of things like when you will wake up, whether or not you wake up feeling refreshed, et cetera. Let's-

Samer Hattar:

And that's why ...

Andrew Huberman:

Yeah.

Samer Hattar:

I'm going to break it on your show, Andrew, that I'm going to tell you, I think there is something else that people need to think about, which is the tripartite model. That this model incorporate three components which we talk about in details that allows us humans and all animals to incorporate the circadian clock and its relation to light, the homeostatic drive, and the direct effect of the environment, which includes stress, light, all kind of stuff. They have to be incorporated together. If you think, that's what I think right now. If you think of one alone, you will always miss something.

Andrew Huberman:

Okay.

Samer Hattar:

And when you think of them as a whole, things really become clear. It's actually quite amazing.

Andrew Huberman:

Okay, well we will definitely want to hear about your tripartite theory and go into detail about this homeostatic mechanisms. I want to make sure that for people who are thinking now, I'm sure, about light and how it impacts them. So, the morning light-viewing behavior, I like to think we've tacked down clearly.

Samer Hattar:

Absolutely.

Andrew Huberman:

And thank you for that because there's so much information out there, and I've tried to relay that information. Of course, you're my primary source for all things circadian, as well as Jamie and others, of course, and Matt Walker, but I think you've made that very, very clear. Now, let's say I've gotten my morning sunlight. Okay, made my bright artificial light. And throughout the day you said to get a lot of light. So, I'm working at my desk, maybe I'll go out during the day a few times, but I'm working at my computer, I'm doing things. Is there anything about light viewing in the middle of the day that people should keep in mind, or can they just sort of freestyle it depending on what they're doing? Most people are not in a dark room throughout the day.

Samer Hattar:

Yeah. So, my gut feeling, if you got your morning sunlight, you walk from your car slowly, or you walk to work, you didn't wear sunglasses when the lights were still dim in the morning, that you could freestyle it. That even if you don't get a lot of light, there is a way to just ... In the day, you don't have to just worry about getting a lot of bright light. But personally, I like to do that. So, I go out at lunch and have my lunch outside, as well. This reminds the body that here it is even brighter now. But the evidence is that you could literally help your circadian clock by giving lights at dawn and dusk. But again, if you think of the tripartite model, this may be important versus circadian clock, but is it important for your mood? So, that's where I think you need, or the homeostatic drive. So, that's where you need to think about it. So, for the clock, in training your clock, you literally can entrain it only by the dawn sunlight. You actually don't need dawn and dusk.

Andrew Huberman:

Okay, but ...

Samer Hattar:

If you even forget that.

Andrew Huberman:

Yeah, and I appreciate that you're distinguishing between circadian effects and other effects of light.

Samer Hattar:

Yeah.

Andrew Huberman:

You're being very precise, which is appreciated. Until we hear about this tripartite model, which we will cover, for the sake of the discussion, let's treat the light-viewing behavior as, what are the benefits or drawbacks of viewing light for all biological purposes, not just circadian setting? So, in the morning it's clearly going to set the clock. And then during the day, if I understand correctly, the idea is to get as much bright light as you can, because you're feeding it sounds like a sort of light hunger.

Samer Hattar:

Exactly.

Andrew Huberman:

I see.

Samer Hattar:

I love this way to put it. I think there is a weird light hunger, considering that we are not photosynthetic organisms. There is a weird light hunger in animals that they need to measure ... They need measure, and I think that relates to the season because the whole reproduction cycle of animals going to depend on the availability of food in the environment. And if you don't know when the season's going to happen, they don't have calendars, it's going to be very hard to survive. So, I think that's why we have this light hunger. That's a major hypothesis, it's not been tested.

Andrew Huberman:

Interesting. So, then afternoon and evening start to approach. So, I've had this weird experience, maybe you can psychologically or biologically diagnose me now, Samer. So, where if I go into a movie in the afternoon like a matinee, and I come out and it's dark, I notice a significant drop in my mood and my ability to go to sleep. Whereas, if I get some view of the light in the evening, doesn't have to be the sunset, although sunsets are nice, but I get some light pulse in the afternoon, that I have no trouble whatsoever falling asleep.

Samer Hattar:

And this happens in a daily ... On a single time to watch?

Andrew Huberman:

Yeah. More or less.

Samer Hattar:

That's interesting.

Andrew Huberman:

And then you mentioned the camping experiment, where when they went camping they're seeing the sunrise and the sunset. So, what should people do in the afternoon/evening time in terms of their light-viewing behavior?

Samer Hattar:

I mean, the best thing to do is to let the natural light creep into darkness, right? That would be the best. But clearly, that would be inefficient. You want to go home, you want to read, you want to talk to your kids, you want to talk to your family. So, I think it's nice to extend the day. I don't think that's wrong, if you somehow can block that light from affecting your circadian clock.

Andrew Huberman:

So, should people use blue blockers in the evening?

Samer Hattar:

I personally do not like any blockers that take a single wavelength of light. Because again, if you think of a holistic approach, yes the blue blocker is going to prevent you from affecting your circadian clock very much. But then your vision is going to be distorted, because we always see in full spectrum, the sun has this beautiful spectrum, right? And then when you start seeing without the blue, things look yellow, and it can get really weird, right? I personally, I've tried the blue blocker, and I couldn't even wear them. I thought they were just really horrendous, to be honest.

Andrew Huberman:

Well, along the lines of blue blockers, I think a lot of people mistakenly wear them all day long.

Samer Hattar:

Oh my God, that would be very bad.

Andrew Huberman:

A lot of people do that.

Samer Hattar:

That would be very bad.

Andrew Huberman:

A lot of people do that. They think that that blue light is bad. I think that the concept of blue light being bad led to a lot of product development. And a lot of people are just assuming that viewing blue light is what was giving them headaches, when in fact it might have just been looking at screens at close distance.

Samer Hattar:

So, here's the problem. I mean, the blue light got the bad reputation because people who gave a pure blue light showed that it caused hugely retinal damage. But again, if you're using blue light in its pure form, it has a lot of energy because it's shorter wavelength. But we are talking about full-spectrum light. There are ways now where you could change the spectrum of the light and keep it white between day and night and change the content of the color without you noticing. So, you don't even have to affect your vision.

Andrew Huberman:

So, how would you go about doing that?

Samer Hattar:

So, you just lower the level of the blue light. You don't have to eliminate it.

Andrew Huberman:

So, just dim the lights?

Samer Hattar:

Dim the blue, then increase the yellow, but keep all the colors in a certain white. So, could have different warmness of white. And people know how to do this, physicists know how to do this. People who work with light know how to do this.

Andrew Huberman:

Well, maybe somebody in the wellness, slash ... I don't like the word, but biohacking or optical community will do this. I think it's really important, I see so many people wearing blue blockers.

Samer Hattar:

They have meetings now. I don't know why they love ...

Andrew Huberman:

Well, I think they're just uninformed. I think, frankly ...

Samer Hattar:

And to be honest, it's easy. It's easier to explain to somebody if ipRGCs respond mostly to blue, remove blue, you'll be fine, right?

Andrew Huberman:

Right. Right.

Samer Hattar:

But that's not as simple as that, because they also receive rod and cone input. So, you want to actually ... And we could go into details that's boring for your listeners, but it also affect the adaptation properties of the whole retina. So, you don't want to do something so drastic that you take just one color of the spectrum. It just seems very counterintuitive to me to be honest.

Andrew Huberman:

You've told me before as well that just because these intrinsically photosensitive, circadian-setting ganglion cells respond best to blue light, if the light is bright enough, because they also get input from other components of the eye, it doesn't matter if you block the blues.

Samer Hattar:

Yeah.

Andrew Huberman:

If you're looking at bright light at night, you're going to disrupt your circadian cycle.

Samer Hattar:

Absolutely. And that's why I didn't want to go into the boring details, but themself, the photo receptors have a wide range of responsiveness. So, they are most sensitive to blue light, but that doesn't mean they don't respond to green light or to shorter than blue light. They respond to very, very wide spectrum with different sensitivities. So, unless you understand the system, just removing 480, I don't think it's going to do anything.

Andrew Huberman:

480 nanometers?

Samer Hattar:

Yeah.

Andrew Huberman:

Yeah. So, your home is a cave at night, basically.

Samer Hattar:

It's a nice cave.

Andrew Huberman:

It's a nice cave with candles, right?

Samer Hattar:

And I watch TV [inaudible 00:46:13].

Andrew Huberman:

And you and your cats and your lovely wife, who I know who's also a phenomenal scientist in her own right?

Samer Hattar:

Thank you. Yeah, she is.

Andrew Huberman:

She is. But you do keep your home quite dimmed to dark at night.

Samer Hattar:

Yeah. In fact I did go to meetings with some of my friends who work on this, and they really struggled with me. They said, we could have broken our legs living in the same light environment that you do. So, I am an extreme, but I measured it for myself, and I asked Rejji, my wife, if she's okay with it. She also liked the dimness, both of us can see well in dim conditions, and that helps us a lot. But I think you have to measure it for yourself. You really have to do ... It's a very simple experiment, just try to dim the light as much as you can. I call it the minimum amount of light you require to see comfortably.

Andrew Huberman:

And that's how you want your environment ideally at night.

Samer Hattar:

This is what I think is the game changer. If you reach to a level where it's just barely, you are literally on the cusp of seeing uncomfortably versus seeing very comfortably, you are going to be very much better than ... I don't like to make it completely dark. I think complete darkness induce anxiety in humans, to be honest. So, I don't like complete darkness. In fact ...

Andrew Huberman:

Kids don't like complete darkness. They like a nightlight.

Samer Hattar:

Even animals. Even nocturnal animals don't like complete darkness. I mean, we have studies in animals that are nocturnal, that if you put them in complete darkness for several weeks, they have severe anxiety and depression-like effect. So, keep the light dim, use red light that is very dim if you want to keep the room for sleeping. Red light that is very dim has very small effect on circadian clock. And below 10 lux of red light literally doesn't affect sleep at all. So, there are ways to do it. We need to educate the public, and I feel like you literally need a whole lecture to just explain to the people how to deal with life, because it's not as simple as people think.

Andrew Huberman:

Well, that's what we're doing here.

Samer Hattar:

Yeah.

Andrew Huberman:

We're stepping through it piece by piece. And the reason we're doing that is because it's not as simple as saying just block blue light or get a lot of light during the day and minimal at night.

Samer Hattar:

I mean, just put it in perspective to tell it. We only have three different cones in our retina that respond to three different colors. We call them red cones, for simplicity, green cones and blue cones. Yet we have only three of these, but we could see massive pallete of colors. So, that tells you something. If the system was just simply about a single color and it is just removing 480 or just blue is sufficient, then we should only see in red, yellow, and blue. We shouldn't see all these different hues of color. But because the system is not that, we see all these different colors. And that's why it's important to remind people that the white light is made of many different colors. It's actually like the rainbow, that's why you see the rainbow. It's made of many colors. White light is never truly white, it's made of a lot of different colors.

Andrew Huberman:

It's like the Pink Floyd album cover [inaudible 00:49:24].

Samer Hattar:

Exactly. Exactly. Exactly.

Andrew Huberman:

So, dim at night, maybe dim red light, ideally, or candlelight. Find that minimum required light level.

Samer Hattar:

Test it. Just make sure when you lower the light, sit for at least 10 to 15 minutes, let your system adapt. Because if you had it bright light and you switch it off, surely you're going to suffer because your system didn't adapt it. It was used to very bright light. So, you want to engage your rods, which take a long time to dark adapt. So, that's why I tell you, just wait a little bit. Don't just switch it off there. I don't say put it on, put it off, sit down, wait for 10 minutes, ideally 15 minutes, and then see how you see. And then once you do that, you will notice that actually, yeah, I could see quite well even with much less light.

Andrew Huberman:

What do you do regarding screens?

Samer Hattar:

Yeah. That's the hardest thing again. I mean, there are beautiful programs that change the whole intensity and color of the screen. These could help dim your screen at night to the lowest part. I mean, yes, you won't see it when you wake up in the morning, but then you can increase the intensity. So, try to decrease. I mean, just what we were talking about, think of light intensity, duration, color and time of day. You really have to keep these four things together, right?

Andrew Huberman:

We've roomed together at a couple meetings from time to time, no longer, because one of us, not to be named, has a severe snoring issue that made the other one pseudo-homicidal. You can guess who that was. But I've seen you check your phone after dark once or twice, and you did it by sort of pointing your phone away from you, right?

Samer Hattar:

Exactly. Yeah, absolutely.

Andrew Huberman:

And actually, I'm sort of half joking ... And you dim it quite a bit.

Samer Hattar:

I dim it quite a bit.

Andrew Huberman:

I'm sort of half joking, but it actually makes sense that if you shine a flashlight in your eye, it's much brighter than if you shine a flashlight [inaudible 00:51:24].

Samer Hattar:

Light only goes in direct line. So, if you just look on the side, most of the lights is going to go this way, and you're on the same as me.

Andrew Huberman:

Okay. And as silly as that might seem to people listening, I mean what it means is that getting bright light in your eyes at night is something that you really want to avoid. But there is the reality that ...

Samer Hattar:

And even when I check sometimes, if I have something, and I check it so fast and switch it off so fast. So, I'm also aware ...

Andrew Huberman:

Not my messages.

Samer Hattar:

I'm also aware on the duration, right? So, duration, intensity, color, and time of day. Ideally, I should not check iPhones and iPads. I don't use iPad at night because it's hard to lower it enough because it's a huge. But even my iPhone, I try not to use it at night. And once it becomes 8:30 or 9:00, I don't look at it at all.

Andrew Huberman:

Unless it's World Cup or Euro Cup, in which case Samer's on 24 hours, everybody.

Samer Hattar:

That's only every four years.

Andrew Huberman:

He's a big soccer fan. All right. This has been incredibly, no pun, illuminating. Let's talk about the relationship between light and some of these other noncircadian or pseudo-circadian effects. And we will try and link those. But you had a, what I consider, absolutely landmark, beautiful paper published in Nature a few years ago showing that if you disrupt the exposure to light, or the timing of the exposure to light, that there are dramatic effects on the stress system and on the learning and memory system. We could talk about each of those separately or together. What are the effects on stress and the effects on learning when light-viewing behavior and sleep-wake cycles are disrupted?

Samer Hattar:

Yeah. So, just to remind you, you know that, but to remind your listeners that I was trained as a circadian biologist. So, I really was indoctrinated into thinking that light has to affect the clock, which then cause all these different effects. So, that's what I believe. That's my dogma. That's what have made me really happy.

Samer Hattar:

And then Tara LeGates and Cara Altimus joined the lab, and we started discussing a lot of data and we said, "What if there is a direct effect of light that we are missing independent of the circadian clock?" So, this is not an easy question to ask and to answer, because as we've been talking all along, light affects the circadian clock. So, how could you give light at different times of the day and not mess up the circadian clock?

Samer Hattar:

Luckily, we came up with such a way, and that's why it was important to do these experiment the way we did them. And we proved that this light dark cycle does not disrupt the clock. There is still a circadian rhythm, and does not cause sleep deprivation. And yet, surprisingly, if you give light at the wrong time of the day, even without disrupting the circadian clock or without causing sleep deprivation, as you mentioned, you get huge mood changes in the organisms and you get learning deficit. So, this really, and at the time, people have really hit us hard. I mean, it was really hard to publish this work and you could ... Yeah.

Andrew Huberman:

Well it came out in Nature. So, in the end you prevailed. But I want to make sure that I understand. So, you're saying that, yes, there are effects of light on the circadian rhythm.

Samer Hattar:

Absolutely.

Andrew Huberman:

Meaning sleep and wakefulness?

Samer Hattar:

Yes.

Andrew Huberman:

And their timing. However, there are direct effects of light on mood that can be dissociated from the effects on sleep and waking.

Samer Hattar:

Absolutely.

Andrew Huberman:

So, if I interpret that correctly, that could mean that when we view light, and how much light, could make us feel happier or less happy or even depressed, stressed, learning, et cetera,

Samer Hattar:

Bingo.

Andrew Huberman:

Even if we're sleeping and waking up at the appropriate times.

Samer Hattar:

Bingo. I mean, eventually, because we're talking about the whole system, eventually when you start having the other problems, you also develop sleep problems. But you are absolutely right. And in fact, now research from Diego Fernandez in the lab have found that, now we know that they actually require different brain regions. So, we don't only have a theory, we don't only have a light environment that showed they can be dissociated. We know that they use completely different brain regions. So, the SCN that I told you about earlier, the place where the central pacemaker is, the one that receives direct input from the retina through the ipRGCs to adjust your circadian clock, is not the area that receives the light input for mood regulation. It's a completely different brain region.

Andrew Huberman:

What's the brain region called?

Samer Hattar:

So, the brain region, we called it the peri-habenular nucleus. I'm not so sure how good or bad the name, but doesn't matter, is the PHB. And what's really amazing, this region also receives direct input from the ipRGCs, but projects to areas in the brain that are known to regulate mood, including the ventromedial prefrontal cortex, which has been studied for many years to be impacted in a human depression. So, just by this amazing serendipity to find that a region that is so deep in the advanced brain. The prefrontal cortex is your executive brain, one of the most elaborated in humans. To see that they receive input from these ancient photoreceptor was stunning to us and told us how much we didn't understand the importance of light on a human behavior.

Andrew Huberman:

So, how does that finding inform daily protocols for you or for other people? I realize you can't leap to always from one paper to daily protocols.

Samer Hattar:

Yes.

Andrew Huberman:

But if light, indeed does control prefrontal cortex, executive function, learning, stress and mood. Let's say I'm waking up each morning and I'm sleeping, what should I do differently?

Samer Hattar:

That's why we came up with the tripartite model. Because yes, we could think about just adjusting the clock with lights in and being dark throughout the day, but that may not be important for your whole physiological function. So, now if we include these other effects of light, that's why I prefer to still get a lot of light in the day. I don't want to be in very dim light condition throughout the day.

Andrew Huberman:

I see.

Samer Hattar:

So, even though it doesn't affect your clock, as you beautifully said, Andrew, it may affect your mood and learning and memory. It may affect your alertness level, which is going to allow you to learn better. It may affect your homeostatic drive, maybe your homeostatic factor will go higher so you could sleep earlier. So, it's important to think of light as stimulating all these brain regions, which means it's producing more activity, which in reality, this is how people think of the homeostatic drive. That the more active you are, the more the homeostatic drive is built up, the better you sleep.

Samer Hattar:

So, that's why we came up with the tripartite model, because as a circadian biologist, I only thought of light through the circadian clock affecting behavior. As a sleep biologist, they only thought of the homeostatic drive affecting sleep, affecting behavior. And for people who study light for vision and other foundations, they thought only of the environmental input. But now if you put them all together, you get with this tripartite model, where it's really mind boggling and it makes so much sense. The organism doesn't want to depend on a single component. But if you could incorporate these three together, you could have a beautiful system that is well-adapted. So, let me tell you the sleep-wake cycle, right? So, we know there is a homeostatic drive to affect sleep. You've had beautiful talks about that.

Andrew Huberman:

Which is basically the longer you're awake, the more you want to be asleep.

Samer Hattar:

So, that's your homeostatic drive. We've talked about the circadian influence of sleep and the fact that light dark cycle affect the circadian system, which eventually affects sleep. So, these two components are well understood. Now, the third factor is your direct light or environmental input. How much stress, how much light you get from there also can highly impact sleep. So, even if you have a good circadian and homeostatic drive, if you're getting light at the wrong time of the day, or if you're being stressed and thinking, then your sleep is going to suffer. So, you have to think of the three together to have a beautiful sleep wake cycle. And that's why we came up with the tripartite model.

Samer Hattar:

The same thing happens with feeding. I could beautifully put it to people. Your hunger, your energy level is measured by the arcuate nucleus. Your daily intake of food is, again, dependent on the SCN and light dark input. We found that if food is not available, there is yet a third input that is not dependent on the SCN, not depending on the arcuate, depending on a completely different brain regions. So, the animal can actually start looking ... or the human can start looking for food when it's scarce even at time when they are not supposed to be active. So, that's how the organism think; they have to evaluate multiple inputs for them to decide what is the best physiological outcome at that moment, at that season.

Andrew Huberman:

I see. So, I want to get into arcuate and feeding, but just to keep ... make sure we can keep our hands around this tripartite model. So, if I understand correctly, we've got the circadian influence, then you've also got the drive to sleep.

Samer Hattar:

Right.

Andrew Huberman:

Actually, one of the ways that I think that can be best understood is if somebody ever pulls an all-nighter, they get tired around 11 or 12 or so, and then very tired around 3:00-4:00 a.m. But then even if you stay up, sometime right around seven or 8:00 a.m., your normal wake-up time, you start to feel alert again.

Samer Hattar:

Exactly.

Andrew Huberman:

And that's because the sleep drive is extremely strong, but there's a circadian rhythm that drives wakefulness in the morning.

Samer Hattar:

Exactly.

Andrew Huberman:

Okay, so that's two of the components.

Samer Hattar:

Right.

Andrew Huberman:

Before we get into the feeding component, I want to talk about these direct effects of light on mood. Okay. Diego Fernandez's data and this peri-habenular thing.

Samer Hattar:

Sure.

Andrew Huberman:

So, let's just, for the moment, set aside the tri part of the tripartite model and just focus on what are the direct effects of light on mood. And the way that I interpret what you've said so far is that the protocol that emerges from this, if one is trying to optimize their mood, is yes, see light — view light, I should say — early in the day in order to set your circadian clock, maybe also in the evening as well. And of course, avoid light at night, get it as dim as possible. However, you said it's also a good idea to get as much bright light during the day as you safely can in order to improve your mood, independently of regulating your sleep-wake cycle.

Samer Hattar:

And that's a hypothesis. Here's the problem where it is not going to be as satisfying as the circadian, is that, as you know, this brain region has been discovered very recently.

Andrew Huberman:

Habenula?

Samer Hattar:

The peri-habenular region.

Andrew Huberman:

Well, we've known about it a long time, but nobody knew what it did.

Samer Hattar:

So, we knew about the habenula, but that's why the name is confusing. It's actually not the habenula itself, it's the peri-habenula.

Andrew Huberman:

Oh, near the habenula.

Samer Hattar:

It's near the habenula.

Andrew Huberman:

Why don't you just call it Samer Hattar nucleus?

Samer Hattar:

I should have, I don't know why. Don't ask.

Andrew Huberman:

Maybe because if you do that, it's not okay. Okay, so for here ever after, the peri-habenular nucleus, we should probably call it the Hattar ...

Samer Hattar:

The Hattar-Fernandez.

Andrew Huberman:

How about Hattar-Fernandez nucleus. Okay, this is nerdy science attribution stuff, but I'm just going to call it the Hattar nucleus. Wikipedia, line it up. Okay, so this structure is taking light, and independent of sleep rhythms and circadian rhythms, it's driving changes in mood.

Samer Hattar:

Something.

Andrew Huberman:

How does it do that? Is this through the dopamine system, the serotonin?

Samer Hattar:

We really ... We still recently, we haven't identified this region very well. We don't know what light does to it. We don't know how it interacts. So, this is an area that is ripe for discoveries and we are working on this right now. But that's why I said it's not satisfying. This is like the function of sleep. Why do we sleep? We know sleep is very important to us, but we still don't have a satisfying function of why do we sleep, right? We have ...

Andrew Huberman:

The "why" questions — I think it's our good friend and colleague at University of Washington, Russ Van Gelder, who always says, "When somebody asks why, the best answer is just to say, 'I wasn't consulted at the design phase.'"

Samer Hattar:

Yeah, exactly.

Andrew Huberman:

Right. None of us really know why.

Samer Hattar:

No, but the point is, maybe I shouldn't have said why. What is the function of sleep? It's still very hard to know. What is the reason organisms have to go offline for so long? People assume it's for repair, assume it's for learning and memory, assume all kind of stuff. But there is really no clear function for sleeping. There is no clear function for sleeping. I mean, if you talk to people, there are hypotheses.

Andrew Huberman:

I mean, all we know is that if you don't sleep, or your sleep is very fractured, you get messed up.

Samer Hattar:

And you could die even, right? I mean, it's really bad if you don't sleep. But we don't know what is the function. What is that sleep have done to organisms that couldn't have done with rest? What if you just could rest without sleeping, just sit down and rest.

Andrew Huberman:

Well, my lab's trying to figure out whether or not these non-sleep deep rest protocols can compensate for sleep.

Samer Hattar:

So, that would be ...

Andrew Huberman:

I mean, obviously sleep is better, but many people are not getting the sleep that they need.

Samer Hattar:

Right.

Andrew Huberman:

Okay. So, if people are sensing that Samer and I are about to start talking over each other and arguing, that's always the goal when we talk, right?

Samer Hattar:

That's right.

Andrew Huberman:

Unlike other scientists I interact with, when Samer and I get together, it's considered a successful conversation if we get into a big fight and then go for a big meal, where I pick the restaurant. Okay. So, let's talk about food and eating and appetite. You had yet another ... Yes, I greatly admire your success in this way. Yet another incredible discovery showing that there are effects of light on appetite and feeding behavior. Maybe you could just summarize those results for people.

Samer Hattar:

Honestly, that paper is the one that allowed us to come with the tripartite model because we were thinking completely wrong about it. We wanted this experiment. It'd be fun for your audience to hear why we started this experiment. Remember that when we discovered ipRGCs, we figured if they are the only relay to entrain the circadian clock, then you could kill them and have an animal opposite to the one that we spoke, or human opposite to the one that we spoke about earlier, where instead of having no pattern vision and have circadian photoentrainment, we could produce an animal that have pattern vision, but no circadian photoentrainment.

Andrew Huberman:

So, circadian blind?

Samer Hattar:

Circadian blind, but pattern sighted. And we succeeded in that. The problem when you have these animals, which I've told you many ...

Samer Hattar:

The problem when you have these animals, which I've told you many times already, is that they don't adjust to the day/night cycle. So doing experiments on them become very complicated.

PART 2 OF 4 ENDS [01:06:04]

Andrew Huberman:

What is their behavior like if you don't have these cells? Are they awake and then asleep, awake and that's it?

Samer Hattar:

They just drift, like the humans we've talked about.

Andrew Huberman:

They think they're in Las Vegas, no clocks are watched.

Samer Hattar:

They drift, exactly.

Andrew Huberman:

They stay up later every night and go to sleep.

Samer Hattar:

They come either, depend their clock, if it's their clock is shorter, they come in earlier. If their clock is longer, they come in later.

Andrew Huberman:

So they're really messed up.

Samer Hattar:

They really don't adjust to, if they were in the wild, they'd be eliminated in a second, right? There is no way they survive. So me and Diego started talking, and we're like, what if we use non-light in training agent, and what is the strong non-light in training agent? Food. So we thought that the light defective animals will have more sensitivity to food in training because, as you know more than me, this is an area that you've worked really well on. For vision, if you are image blind, your hearing and somatosensory get improved, right? The lack of vision improves your hearing and sensation. But we found actually that if you don't have the light system, actually you're feeding, the food ability to train the animal goes completely to the ground. Completely opposite to what we predicted.

Andrew Huberman:

So light-viewing and feeding behavior are interacting in ways that support one another.

Samer Hattar:

And that's why we came with the tripartite model. We figured it's different than sensation of the environment. When you sense with vision, vision and hearing interact, but your vision is a real, full modality. You want to see, that's what vision want to do. You want to hear, that's what hearing want to do. You want to sense, that's what sensing want to do. But for the circadian system, light, food, all these in training agent, they somehow have to interact to keep a coherent system. You don't just assume if you remove light, this one is going to be stronger. No, they need to know each others. The light informs when the animal's going to eat.

Andrew Huberman:

Well, what I like about this so much is that in the other world outside of science in which I don't really exist in, but that I see a lot of this kind of wellness stuff with all this mind-body integration stuff. It's interesting because people view the body more as a system. A system of organs that interact as opposed to the way that standard science and medical profession is like you work on the liver or your ear, nose, and throat or heart and lung or brain.

Samer Hattar:

Right, that's a great way of thinking.

Andrew Huberman:

But the biology is integrated.

Samer Hattar:

Yeah.

Andrew Huberman:

And so for somebody who's interested in affecting their eating behavior, something that you are familiar with and that we will talk more about your experiences of in a moment. How should they use light in order to adjust their eating behavior?

Samer Hattar:

So now that I've told you about all these interaction between the different inputs of the circadian clock, just you think about it as an engineer. What would be the best thing? The best thing is to know when your food times happen in the day. When should you get light and where is your circadian ... when is your circadian clock in your system, right? So if you eat at very specific times of the day, that's another signal that is telling your body, your clock, you're in a certain time of the day. So if you're having lunch at the correct time every day and you're getting bright light, now you have two systems that are informing your clock. Your clock is going to be better.

Andrew Huberman:

So regular meal times.

Samer Hattar:

Regular meal times that fit your circadian clock. And in fact if you do that, when I started doing this, and it helped me lose weight, is that I'm exposing myself to the right amount of light dark cycle. I'm eating at regular time. It is amazing you will be not hungry. Let's say you eat at noon. You will not feel any hunger at 11:45, and then all of a sudden the hunger jumps in. This is clearly not an energy issue because it could not be that drastic, right?

Andrew Huberman:

No, the desire to eat is mainly driven by these cues, these hormone cues. That are very exquisitely timed to sleep-wake cycle but also to light.

Samer Hattar:

Exactly. And you know in the wild you could imagine why energy level through the arcuate nucleus.

Andrew Huberman:

You should explain to people what the arcuate is, because I don't think we've done that adequately. The arcuate nucleus is an area of the hypothalamus that drives hunger and feeding behavior. And what we're talking about is the fact that it's taking cues from your viewing of light, believe it or not, is impacting your level of hunger. And this is a nontrivial way in which your timing of hunger and amount of hunger is regulated by when and how much light you view. So let me ask you a couple practical.

Samer Hattar:

Can I just, this is really, before you ask me — sorry, Andrew, we said we're going to fight. But to me is the interesting thing to think about it. In the wild when you didn't have the availability of food that we have, the argument plays a huge important role because if you weren't successful in getting food, then the arc is going to tell you, look, you have to take risk and go get food because your energy level is very low. And that's great, that's tons of great research about that. But I think what's missing is the fact in humans we are not getting to a situation, most of us, we're not getting to a situation where we have low energy levels. Most of the time actually we eat not because we want to, because we are really have low energy, but because we want to eat. So I think that's why I feel that the timing is very important for us because we always have enough energy level for us to eat.

Andrew Huberman:

Well, I mean I enjoy eating so much that I'll eat just for the sensation of chewing.

Samer Hattar:

True.

Andrew Huberman:

I mean I enjoy the taste too.

Samer Hattar:

True. Absolutely.

Andrew Huberman:

And I enjoy the social aspects.

Samer Hattar:

Absolutely.

Andrew Huberman:

And those are a part of it. But I literally enjoy the physical act of chewing.

Samer Hattar:

Absolutely.

Andrew Huberman:

Which explains a lot. Okay, so how regular are you or do you recommend people be about meal times? Because what I'm hearing is that light-viewing behavior is pretty straightforward. Get a lot of light in the morning and throughout the day, minimize it in the evening and at night, generally speaking, for sake of mood and circadian rhythm. But for sake of regulating timing and quality, I should also say of food intake. Because people clearly make better choices about food intake when they are anticipating a meal and they aren't constantly hungry. And so the ability to regulate hunger for particular phases of the circadian cycle is quite valuable for all people. Not just people trying to lose weight, but all people. Are we talking about down to the minute?

Samer Hattar:

Absolutely not.

Andrew Huberman:

All right. Plus or, so 12 noon is my normal lunch, let's say, plus or minus.

Samer Hattar:

Half an hour.

Andrew Huberman:

Okay. So eat around between 11:30 and 12:30.

Samer Hattar:

If that's the time. And it depends if you also do multiple meals, remember three meals, that's decision that somebody came up with. I don't know why.

Andrew Huberman:

Nowadays people are, fewer people are doing that. I think given our friend Satchin Panda's work.

Samer Hattar:

Right. I mean so you could have two meals. You could have very multiples meals that are distributed across your active time. I agree with Satchin Panda's work. That try to avoid eating when your system is supposed to be relaxing, when you're supposed to be at nonactive time. So limit your eating to the active time of your cycle. And that seemed to be, and Joe Takahashi is doing some beautiful stuff on this. That seemed to be incredibly important for aspect of the circadian.

Andrew Huberman:

And for health.

Samer Hattar:

And for health.

Andrew Huberman:

Yeah. I mean Satchin, we're referring to Satchin Panda's work. He wrote a beautiful book called "The Circadian Code." Maybe Samer, with some luck, you'll write a book as well, meaning the world will be lucky to have that book. But Satchin's data really strongly point to the fact that liver health, brain health, metabolic factors, and endocrine factors of various systems and organs all seem to benefit from having a period of each 24-hour day in which we are not eating anything and then eating at very regular, set times.

Samer Hattar:

Absolutely.

Andrew Huberman:

Let's talk about eating and meal times and let's move a little bit away from the science for the moment, although we will return to it and talk a little bit more about your experience with eating and meal times. So you're looking in good shape lately.

Samer Hattar:

Thank you.

Andrew Huberman:

I know you've been putting work into it.

Samer Hattar:

Yeah.

Andrew Huberman:

We talk a lot and you've been exercising and you've been eating well, meaning quality food. You just came back from Jordan, where I'm assuming the food is amazing.

Samer Hattar:

The food is amazing, and honestly, usually I gain a lot of weight in Jordan. But this time I didn't gain any weight, which was really nice.

Andrew Huberman:

Yeah, yeah. When I met you, you were probably about a hundred pounds heavier than you are now.

Samer Hattar:

Yeah, 275 pounds. I'm 219 now. That's crazy. Yeah.

Andrew Huberman:

You had a lot of vigor then, and you have a lot of vigor now. But I know that you undertook a very specific protocol in order to lose the weight. Based on your understanding of the circadian system, and of light, and appetite, and mood, maybe you could just tell us a little bit about what that schedule looks like, and we realized that this is not a prescription for everybody, but you found what worked for you. Maybe just describe those.

Samer Hattar:

I mean honestly, I followed my circadian cycle, right? Of what we've talked about. So I dimmed the light at night, I slept at regular hours, I ate my major food in breakfast and lunch when I'm really active, and I'm really hungry. And at night when I avoid dinner because my circadian system really shuts off at three. I'm an early person. You could give me anything I would eat before three. After three nothing appeals to me anymore. My system is shut off.

Andrew Huberman:

But what time are you going to sleep, and what time are you waking up?

Samer Hattar:

Oh, so in my case is, I should have put this out. I mean I go sleep literally at 9:00 p.m. I mean I literally, five minutes after 9:00 p.m. I'm completely out. And I wake up between 4:30 and 5:00 a.m. So if I extend it, I go to 6:00 a.m. but very rarely, depends on how tired I was.

Andrew Huberman:

And that, as I recall, was an important set of changes for you to be able to regulate your food intake.

Samer Hattar:

Absolutely. Because then I'm having very big breakfast, and again for different people it's different. I have a big breakfast at 7:00 a.m. maximum. So I have a big breakfast, coffee and all the stuff. Then I have some simple snack around 10. Then I have regularly lunch at noon or between noon to one. Then I have another snack at three. And the hardest time to regulate the food is between 12 and three. This is when I really feel hungry all the time.

Andrew Huberman:

This is your equivalent of late evening for most people.

Samer Hattar:

Yes.

Andrew Huberman:

So for me it would probably be between 7:00 and 10:00 p.m..

Samer Hattar:

Exactly. And then at night I'm completely not hungry. But usually, as you said, the beauty, the enjoyment of food, when my wife cooks some really beautiful Indian food I eat, but I'm not hungry. And I notice if I eat with that, I usually gain weight. But if I regulate that at night, I also lose weight. So there is a combination of all these things that help you adjust the input of food, the input of light, the input of the clock, and the drive to hunger.

Andrew Huberman:

Yeah, I appreciate you sharing that. And I want to emphasize that some people are not hungry early in the day. They might be late shifted people in which case eating later in the day will work well for them.

Samer Hattar:

It will work as long as they don't eat early in the morning. That's just, you have to work with your schedule, with your active schedule.

Andrew Huberman:

Yeah. You and I have been talking about this offline for years. I'm glad we're finally having this discussion publicly now. What we're talking about really is finding your ideal sleep schedule.

Samer Hattar:

Exactly.

Andrew Huberman:

And finding your ideal eating schedule.

Samer Hattar:

Exactly.

Andrew Huberman:

And understanding how those two things interact.

Samer Hattar:

And the nice thing, as you said, finding them out is going to help you to understand how they interact. Because we know from the tripartite model that they are all interconnected, and for each person they're going to be interconnected differently. So for each person, for me, if I exercise at night, I'm going to mess up my whole system.

Andrew Huberman:

So when do you exercise?

Samer Hattar:

Morning. Morning works great for me. I mean it's amazing. Morning exercise for me works great. I tried one time because it was easier for me to exercise at night before I leave when the traffic is there from the night. And I think that messed me up because I couldn't sleep well and I couldn't wake up well. And that led to more changes in my food. I gained weight again, actually, believe it or not, even though I was exercising. So I think this really makes me think that you have to think of the tripartite model to see where is the best times and what is the best interrelation between the different component, as you beautifully said. Between your meal times, your light exposure and your sleep that works for you.

Andrew Huberman:

Well thank you for that. Usually Samer's insulting me, today he's complimenting me. I'm going to compliment him right back by saying this is the first time that I've ever really understood how yes, light can control sleep. Yes, it can control mood, yes it can impact feeding, but that it's really about doing the self-exploration to align those in the way that works best. And what I'm hearing, tell me if I'm wrong. But what I'm hearing is that once you understand what gives you the best sleep-wake cycle, then you should exercise during the period of time in which you feel most alert, and if it works for your schedule, ideally you would also eat during the time in which you feel most alert and then stop eating and stop light-viewing behavior as you head towards sleep.

Samer Hattar:

So the only thing I would say that complicates all of this, and that's what makes me sad, is your light exposure.

Andrew Huberman:

Mine personally? No, I'm just kidding.

Samer Hattar:

The people's light exposure, this is what complicates it. Because you are not going to be able to figure all this out if you're shifting yourself out of your comfort zone.

Andrew Huberman:

By viewing.

Samer Hattar:

By viewing light at the wrong time of the day. So let's say if you were under an ideal natural conditions. You're a person who would sleep later than me, let's say will sleep at midnight and wake up at 8:00 a.m.. Let's say you don't eat anything till noon and as you said you eat late in the evening, then this would be perfect for you. But now see what happens if now you include the light component. Now if you push your sleep from midnight to 4:00 a.m. now you're waking up in the morning and you are actually really not the morning. You're waking up, sorry, at noon instead of 8:00 and the time where you're not supposed to be hungry, now you're going to start eating directly at noon or something like that or even delay it. And now you're shifting your whole cycle and you don't know if this interaction between your sleep feeding and the light dark environment are still going to be maintained or not, and that's the problem that people have.

Andrew Huberman:

So as I'm hearing this, what I'm realizing is most of us, probably me included, are messing up at least one, two, or three of these components.

Samer Hattar:

Exactly.

Andrew Huberman:

But that the probe, the way to figure out what's right for oneself is to start manipulating light exposure.

Samer Hattar:

And I'm going to be honest, I'm biased because I believe that light is the stronger, is the strongest time giver. And a lot of people disagree. Some people think feeding is.

Andrew Huberman:

I always thought that light was the primary zeitgeber, the primary light.

Samer Hattar:

But a lot of people think it's food. A lot of people even sometimes mention social interactions.

Andrew Huberman:

Have they read the literature?

Samer Hattar:

I agree with you. I totally agree with you.

Andrew Huberman:

I mean, my understanding is that light is the most powerful driver of the things we're talking about.

Samer Hattar:

That's why I think we need to regulate this first and everything else fits. And the nice thing is that your sleep/work cycle and exercise tell you really bluntly if you're doing it right or not.

Andrew Huberman:

Tell me more about that.

Samer Hattar:

I tell you more. When I shifted my exercise, honestly things fell apart like never before.

Andrew Huberman:

When you moved from exercising early in the day.

Samer Hattar:

Yeah, it completely fell apart for me. I didn't enjoy exercise at night. My pain tolerance for exercise wasn't as good. I'm talking with N equals one. And I'm aware of this, I've never tested this empirically, but at least to me it really messed up everything. I started having problems. Because my body temperature will go up, and that will affect my sleep. I possibly was running in the gym with a lot of lights, so maybe the light was a component. But for me, exercising in the morning, it's so much better for me. But lot of people can't even think of exercising in the morning. So it depends on when you feel comfortable in your sleep-wake cycle and your exercise. I think that tells you if your system is in synchrony with one another.

Andrew Huberman:

That's really interesting. We're good friends. Our friend Pat Dossett, right, that we both know. Did nine years in the SEAL teams, and he's one of these people says he's happy to go for a run or swim anytime between 4:30 a.m. and 6:00 a.m. And he'll train in the afternoon too because he's a SEAL team guy and they'll do whatever anytime. That's part of the phenotype. But he feels best doing that. I like to exercise mid-morning.

Samer Hattar:

Interesting.

Andrew Huberman:

And I'm happy to skip eating until 12 or one.

Samer Hattar:

Great.

Andrew Huberman:

And I like to go to sleep around 11:30, 12 because I'm a normal human being rather than you who goes to bed at 9:00 p.m..

Samer Hattar:

What about Pat? Actually, I've never asked him what time.

Andrew Huberman:

So Pat's ideal to-sleep time. I've asked him, this would be around 8:30 or 9:00, except now ...

Samer Hattar:

I'm like Pat.

Andrew Huberman:

No, but he has, yes. But he has two young children, two years old and a newborn. And so the cycle is disrupted, right?

Samer Hattar:

Yeah. But that's known, right? I mean the effect of childbearing, and I think that we could talk about this that's more complicated, but that's pretty much, yeah.

Andrew Huberman:

Yeah. I mean I think we need to come up with a new name for chronotype because chronotype implies that it's just about sleep and wake.

Samer Hattar:

I agree.

Andrew Huberman:

Being an early bird or a night owl. And what we're also talking about is how exercise and eating latch onto those.

Samer Hattar:

And the phase relation between them and the phases between different components, as you said.

Andrew Huberman:

Because they interact.

Samer Hattar:

Because they interact.

Andrew Huberman:

Right.

Samer Hattar:

And they don't have to be in the same phase. Let's say my light and food could be very close to each other. Your light and food could be different, right? The phases don't have to be, they can't be plastic. So you have to find this for yourself. You may be a person who eats late at night, exercises late at night, or you may be a person who exercise early, eat later. So it doesn't, as long as the phase is good. That's what you have to find out.

Andrew Huberman:

And if I understand correctly, when you're talking about phase relationship, it means you want to lump exercise, feeding and light for.

Samer Hattar:

And sleep.

Andrew Huberman:

And sleep. In a way that as a coherent and total system makes you feel really good.

Samer Hattar:

Temporally in a great order.

Andrew Huberman:

Absolutely. Yeah.

Samer Hattar:

And I could tell you, to me, is literally getting exposed to sun. Clearly in the morning, clearly at noon, I go out. I keep my windows in the office completely open, eating mostly in the early time of the day and exercising. And literally at the end part of the day, I'm literally in a more thoughtful, vegetative state. I really can't, like after five, I tell my students, if you want to tell me anything complicated, you're wasting your time. My brain just doesn't function. So even though I only sleep at night, but I'm really starting to shut off, ramp down. Really I mean I could send email, talk about brainless stuff. But my power, my energy to do powerful stuff could really drop tremendously. So all my students who know me very well, they put the meetings with me early in the morning because they know this is when I'm on. So everything for me, and for me is very tight. So it could be different from, it's very clustered in the morning. It's all tied together. And literally the remaining part seems to be just a vegetative state.

Andrew Huberman:

You and my bulldog Costello, who unfortunately passed away recently.

Samer Hattar:

Oh no.

Andrew Huberman:

Yeah.

Samer Hattar:

I did not know. That's so sad.

Andrew Huberman:

Yeah. Samer and Costello were good friends. Yeah. Sorry to break it to you here. Yeah, he had a good, long life and he went easy. But he had a circadian clock that basically would just sleep around 24 hours a day, minimal activity interspersed every third day or so. You do have this morning vigor.

Samer Hattar:

Yes.

Andrew Huberman:

And that I think other people are going to have more of an afternoon vigor. Do you think that this can change across the lifespan? The rumor is that teenagers naturally want to sleep in later and stay up later. Do you think that's social rhythm, or do you think that that's actually biological?

Samer Hattar:

Yeah, that's a tough question. I mean it could be both. One thing that worries me is that it seems that if anything, with age this morning rhythm rigor gets stronger.

Andrew Huberman:

You mean you want people become more of morning people.

Samer Hattar:

More morning.

Andrew Huberman:

Why does that worry you? I think that's good.

Samer Hattar:

Because for me, I'm already very shifted morning. I don't want to be one of these 7:00 p.m. to 1:00 a.m. sleepers at some point.

Andrew Huberman:

On the other hand, also kind of nice because it's quiet and you can get work done.

Samer Hattar:

But honestly from 4:30 till 7:30 when my wife wake up, it can be very lonely. Yes, you achieve a lot. But it's quiet outside so I don't want to be at 1:00 a.m. Let's put it this way, I don't want it.

Andrew Huberman:

You can tell Samer is more social than I am.

Samer Hattar:

That's right. That is true.

Andrew Huberman:

But we should touch on that actually. So your wife is, she follows a different schedule.

Samer Hattar:

Yeah.

Andrew Huberman:

And so the social rhythm is important, I think. What should we do? How should we conceptualize, and how should we adjust ourselves according to the social part?

Samer Hattar:

I honestly love this hypothesis that people came up with and Pat's kids reminded me of. Because kids are really going to disrupt your sleep-wake cycle. It seems like there is a chrono attraction, that usually people who attract each others have actually different sleep-wake schedule. And the idea being is that this allows them to take care of their kids throughout the day/night cycle.

Andrew Huberman:

And have a peaceful marriage.

Samer Hattar:

And have a peaceful marriage anyway, right? So I mean we didn't have kids, me and Rejji, so maybe this is, but it seems like evolutionary, it makes sense that if you want to protect your kids, you don't want everybody to be morning vigor and then the kids don't have, so you want it distributed across. It makes sense.

Andrew Huberman:

It's a reasonable argument.

Samer Hattar:

Yeah.

Andrew Huberman:

I've heard that one of the reasons that people think that the clock is not exactly 24 hours, but it's 24 hours, plus or minus 20 minutes or so. Is because we believe that we evolved in clans or groups, villages, whatever, that were about a hundred to two hundred people. And in order to have protection around the early morning hours when we're vulnerable to predation, and in the late night hours, that you would want some individuals of our species to be naturally more like night owls and some more early people. So your theory of parenting is similar in that way.

Samer Hattar:

Right.

Andrew Huberman:

The social rhythm is a powerful rhythm though. Meaning if I go out and I'm tired, let's say I'm tired at 9:30, I don't want to go out. I'm going to need it.

Samer Hattar:

Can I just say something about that? I think the social rhythm is powerful at the obvious levels. It affects your sleep, it affects how much you wake up or eat. But I'm not so sure is as powerful as people think on the clock. Now eventually it'll mess up the clock because now if you're doing a lot of social at night, getting enough light, eating at the wrong time of the day, eventually you're going to have an effect. But I don't think just the social interactions themself have been shown to affect your clock very strongly, for some reason.

Andrew Huberman:

That's good to know. Well, for people hearing this, they're probably getting the impression I'm the night owl and then Samer is the one that's in bed at nine and then wakes up at four. But having attended many meetings with Samer, I can tell you that he's the party animal. So let's talk about that. I mean, let's talk about the fact that you're the partier who's up until 2:00 dancing at these various meetings, which I've seen.

Samer Hattar:

Yeah.

Andrew Huberman:

You're actually a good dancer, I'm told. But what should we do when we do stay up very late for whatever reason? Could be because we had to take a midnight trip to the hospital, an unfortunate reason. Or it could be because you're in the presence of people that you don't see very often, and you go out for a really nice night out on the town and you get to sleep around 2:30 or 3:00 in the morning. How should one get back on schedule? Do you force yourself to then get up and view light at the normal time that you would get up and view light? Or do you allow yourself to sleep in? What's the optimal power.

Samer Hattar:

I would allow myself to sleep in and remember this is a long-term effect. This is something that you live with for a long period. And remember I told you about the experiments we did with the mood. These required two weeks of that light schedule to cause mood disturbances. So these don't happen just in a single day.

Andrew Huberman:

So this is the way you justify staying out late every once in a while.

Samer Hattar:

Well, in the meetings you've seen me, I've done this for five or six days continuously. But what you didn't see that when I came back to my home, it took me two weeks, as if I did a jet lag. So I really do suffer for two weeks after doing a six crazy night of staying up at night, drinking at the wrong time of the day. So it's not that I'm completely okay with it, when I go back, everything goes back. It takes me actually literally two weeks to recover from the circadian rhythm meeting that you've seen me partying at some point.

Andrew Huberman:

Which is kind of ironic, the circadian rhythm meeting people are totally disrupting the circadian cycle, but scientists are human beings too.

Samer Hattar:

So I think if you do it at very little occasions, I think you should not worry too much that this will have lasting impact. And the good news is that if you readjust your schedule, you could come back to it. The problem is when you maintain these wrong schedule for prolonged team and becomes chronic. Prolonged periods of time, that's when you have the problems and the accumulation of the problems. So when you have sleeping problem, you produce metabolic problem. When you have metabolic problems, you produce lack of exercise, and you could see how things can spiral out very quickly, and then it would be hard to come back to it.

Andrew Huberman:

Well certainly sleep disruption is both a symptom of and ...

Samer Hattar:

Yes.

Andrew Huberman:

A cause of almost all mental health disorders.

Samer Hattar:

Absolutely.

Andrew Huberman:

Right. And certainly the metabolic syndromes that people are talking about nowadays, and all of this. It all funnels back to light.

Samer Hattar:

This is what's so remarkable.

Andrew Huberman:

And so we have these devices, and I use my phone and I use my computer. But do you think that the mere dimming of the screen or not interacting with screens after, with say 90 minutes or two hours before bedtime, according to what we're saying today, this should have a profound effect on these factors.

Samer Hattar:

And it does. And I really believe it does. Again, I think as Pat has did these inventions where you get a pouch where you put your phone in a pouch.

Andrew Huberman:

So what Samer's referring to is our friend Pat, this former SEAL team member, that, who's also very impressive person in the landscape of business and family, et cetera, real a superhuman from by any regard, has this habit of taking his phone and putting it into a sealed pouch in the evening. So it's basically a wall.

Samer Hattar:

He sends you actually these sealed pouches. And so that I think is a great idea because not only it'll take away the light from you, but it also take away the distraction. Because you want to repair and recover, and sleep does that. And if you have your phone dinging all the time or the light flashing from it. It's just not getting enough sleep, and you're causing yourself major problems.

Andrew Huberman:

I'd never asked you this, but I realized now that I should have long ago, but I'll ask you now. Why and how did you get into all this stuff?

Samer Hattar:

Yeah, I mean, honestly, first of all, I wanted to study genetics, and I knew I wanted to do PhD in genetics. But I only got accepted in one university at the time. And I joined the learning and memory lab, and I liked learning and memory at the beginning. I worked on the snails and lymnaea and started looking at learning and memory, but then the same lab was looking at this daily variation. I was really struck, you never think about it outside of science. It really struck me that organisms can measure day biologically. That was very shocking to me. And I just really got attracted, and I wanted to see why does this happen? What is the effect of different times of day? And I just stuck with it. It was mind blowing for me who was in medical school that I've never heard about it before. It's really amazing medicine. I think still now, we are very good at looking at stuff spatially, but we are very bad at looking at temporal aspects. So we always like to see images, static images, spatial information.

Andrew Huberman:

Right. Take an x-ray, measure a temperature, measure a blood pressure.

Samer Hattar:

Exactly right. But we don't think of temporal and, you know, talk to John Hogenesch right now, and he's telling you the importance of chronomedicine, or chronopharma, pharma, whatever the word is. And it really just getting the drugs at the right time of the day is going to be essential for our health.

Andrew Huberman:

Do you think that's going to come from using better trackers like Oura Rings, Whoop Straps, these kinds of things?

Samer Hattar:

I love the trackers, but I think there's even more exciting discoveries now. You could take a single blood sample and measure many biological components and figure where you are in the circadian clock. Something that was very hard to do before. So if you have a marker to know where you are in the clock, you could actually understand more the effect of everything. Exercise, feeding, light input.

Andrew Huberman:

What is the marker?

Samer Hattar:

So there are some papers from, what's her name, Phyllis Zee, and from Kramer, where they measure multiple RNAs that are known to tell you what phase of the clock is, or multiple proteins or biological reactions. And depending on a combination of factor, not a single factor, you could tell where you are in the clock. So they could, instead of just measuring temperature or melatonin, just one measurement. And melatonin specifically is also complicated by the fact that melatonin is affected by light and temperature. Your temperature and sleep can be easily dissociable, right? When you travel across different times on your sleep at different times in the temperature cycle. So having multiple components measured will give you a better determination of your circadian phase. And understanding your circadian phase in humans will tell you what is the effect of giving certain drugs at certain times of the circadian phase. So in the future, this is going to be studied at a much higher level when you can determine the face in relation to all the other stuff.

Andrew Huberman:

It's striking to me that in all animals besides humans, if they deviate too much from the appropriate exposure to light and light dark cycle, they essentially don't mate and/or die and/or get killed off. But in humans, we are able to override that, at least to some extent. But the ways in which we suffer appear to be things like obesity, metabolic syndromes, reproductive syndromes that are accompanying the other syndromes, endocrine syndromes and mood and depressive disorders. Is there any effort at the level of the ... nationally, or laboratories that you're aware of, to try and use light in order to improve mood and mental health?

Samer Hattar:

I mean, honestly, this is my mood. This is the thing that I think people, because it's, I say don't take your pill, take a photon. And not, I mean you take pills; it's important. I'm just making it that really we have an opportunity right now with the incredible advances of LED lights, of changing spectra of light, of regulating intensities. And just for simple changes, you could really improve sleep-wake cycle productivity, and still you could actually get more done. Because as we've talked about, when you have all these messed up, now you have to sleep more, but your sleep is fragmented; it's not very good.

Andrew Huberman:

And you can't focus.

Samer Hattar:

You can't focus when you don't have alertness, when you need the alertness. So having all these, you could allow you to do even more actually at the end than less. And that's the.

Samer Hattar:

To do even more actually at the end than less. And that's the exciting part of it.

PART 3 OF 4 ENDS [01:39:04]

Andrew Huberman:

One of the questions I get asked most often about is about ADHD. You know, I think there's a lot of self-prescribed as well as clinically prescribed ADHD. People are having a tremendously difficult time focusing, and not just because they're sleepy, they just can't seem to anchor their attention. And there could be multiple reasons for this, but there are now several clinical trials ongoing using light to try and anchor people's attention and mood and well-being, for sake of focus. And I think that while I love this saying that you mentioned: "Take a photon, not a pill," and with due respect to the need for pharmacology for certain people, I think most people just haven't really dialed in their relationship to light in a way that allows them to rule out whether or not they need medication.

Samer Hattar:

Absolutely. Absolutely. That's the best way to put it. I can't add to that.

Andrew Huberman:

Let's talk about jet lag, but not in the context of, okay, if somebody's traveling from Europe to Japan, or from the East Coast, because that varies tremendously, right? I mean there's as many different variations on travel as there are individuals out there, and with goals and jobs, et cetera. But rather, let's talk about what are the two or three things that people can do to adjust their schedule quickly.

Andrew Huberman:

Yesterday I called you and said, "Look, I know somebody who's traveling six hours." I won't even mention in which direction because I don't want people to anchor to that example. And you described some very simple tools of viewing light a little bit earlier than normal and getting on the local food schedule, et cetera, that would allow them to shift more quickly.

Samer Hattar:

Exactly.

Andrew Huberman:

And the reason I want to have this conversation is, yes, for the travelers and for the shift workers, but mostly because of the fact that you've proven again and again that people are disrupted in their circadian behavior at home. So what are the, aside from what we've already talked about, how can one adjust quickly to a new schedule? Like let's say fall classes are starting, you start a new job, or you have a baby or a puppy or whatever. What is the best way to shift the clock quickly?

Samer Hattar:

So it's very simple as we've talked yesterday. So imagine you're in the outside with no environmental, with no industrial light. If your body thinks you are in early evening and you see a bright light, what does this tell you? Oh wait, this is not early evening yet. It's still early afternoon or late afternoon, so I have to delay my clock to go back to late afternoon. So if you get light early in the evening, it delays your clock. So what does-

Andrew Huberman:

Meaning that it makes you want to go to sleep later.

Samer Hattar:

Yes, it delays your clock. So you are in New York, right? People in Italy have an advanced clock because they are six hours ahead of us. So if you are in New York and you get light early in the evening, you delay even further from Italy. So now you're delaying away from Italy. Now the same thing happens, let's say you thought dawn came up, and you thought it's already dawn, but it was let's say three o'clock in the morning or four o'clock in the morning. And then you get a bright light, and you say, oh wait a minute, dawn is not up yet so I should advance my clock. Or at night, but I'm getting bright light so I should run because dawn is already up. So then later in the night, later in your night, and actually it just happens that humans, you get a temperature nadir later in the night, low temperature in your body, after that lights start advancing your clock.

Samer Hattar:

So if you want to go to Italy, instead of getting light early in the evening, you want to get light after the temperature low. So you could advance your clock even before you go to Italy, and you're catching up to the Italians just by using light. It's as simple as that.

Andrew Huberman:

Great.

Samer Hattar:

So you could do it for every region. You could calculate how much they are advanced of you. You could know how much these light shifts happen per day and you can calculate what you need to do. Very simple math to adjust either in direction of delaying, if you're going from New York to California, you want to delay your clock, or advancing if you're going from New York to Italy.

Andrew Huberman:

So in order to make that a visual, and because a lot of people are listening to this, not looking at it on video, we will put a zero-cost downloadable figure of this on the hubermanlab.com website related to this episode. But I think I can summarize it in language as well. If I understand correctly, what you're saying is if your typical wake-up time is, say, 7:00 a.m. then your low point in temperature probably occurs somewhere around 5:00 a.m. And if you view light right around then, it's going to essentially advance your clock.

Samer Hattar:

Yeah. Because then your body thinks, oh, it's seven o'clock, so advance your clock by one to two hours.

Andrew Huberman:

But if I were to view light, say at 3:00 a.m., then it would probably delay my clock.

Samer Hattar:

Yeah.

Andrew Huberman:

Okay. And then let's say I land in a new schedule, I want to adjust to a new schedule. Let's say I didn't manage to do anything with my light viewing before I went, I didn't anticipate the trip. Suddenly I'm on a new schedule. I was told that one of the ways to help shift the clock and to avoid gastrointestinal issues is to eat on the local schedule, to start basically behaving like a local, even though your circadian clock will take a little bit of time to catch up.

Samer Hattar:

Right. Absolutely. But you have to remember the light. So now that we explained it very simply, let's take a very simple example, right? New York to Italy, that's a simple example. New York time, Italy time, six hour difference, right? So let's say you fly from New York at night, you reach Italy at eight o'clock in the morning. What is the time in your New York time, although you reach-

Andrew Huberman:

Six hours back.

Samer Hattar:

Six hours back.

Andrew Huberman:

It's 2:00 a.m.

Samer Hattar:

It's 2:00 a.m. So when you land Italy, you want to avoid light like the plague. Yeah, you could eat, but you really don't want to get light.

Andrew Huberman:

Right, cause otherwise it's going to delay you.

Samer Hattar:

Delay is going to send you to California instead of sending you to Italy.

Andrew Huberman:

And so this is such a key point. If anyone's confused about this, we will put some diagrams up. But what Samer's saying is so crucial. Just because getting bright light in your eyes early in the day is really beneficial when you're at home, when you travel to a new time zone, you have to take into account what your body thinks, excuse me, you have to take into account where your body thinks you are. And so if you're looking at the Italian sunrise having just flown from New York to Italy, and you didn't prepare for that trip by waking up a little bit earlier in anticipation-

Samer Hattar:

Multiple days.

Andrew Huberman:

And you view light at 2:00 a.m., excuse me, at six or 7:00 a.m. Italian time, beautiful Italian sunrise, you are going to delay your clock. You're going to basically throw yourself back to California, but you are in Italy. You're going to throw your biology back to California, and you are going to be up in the middle of the Italian night and you're going to be miserable.

Andrew Huberman:

I'll tell a brief anecdote, because I called Samer in desperation a few years ago. I traveled to Abu Dhabi, NYU Abu Dhabi, to give a seminar, 12 hours out of phase; it's a 12-hour flip. And I thought I could just muscle it. I thought, I'll get up, just view sunlight when the sun comes up. And I fell apart mentally and physically, and Samer came to my rescue. I called him, I said, "I don't know what to do," and he said, "Go to the gym at the local dawn, work out, eat, and then view sunlight starting the next day." And that basically got me onto schedule. So I used food and exercise to adjust myself, because my light-viewing activity was just completely out of whack.

Samer Hattar:

Yeah. And we talked about other details, so you have to calculate it, but you're absolutely right. I mean, it's very important to avoid getting the wrong light information when you're trying to adjust your body; because otherwise it shifts you to the other side. Absolutely right.

Andrew Huberman:

Well, you are one of these people that has such vigor. It's one of these things where having known you all these years, you have a tremendous capacity for work and for soccer and for arguing, respectful arguing. And sometimes it's-

Samer Hattar:

Getting worse with the age.

Andrew Huberman:

Yeah well, we could talk about that offline. But I think a lot of your vigor, and a lot of your ability to work hard and focus and really do so many things at an impressive level, is because you think about these issues, and you think about when you're going to be optimal for focus. When you're going to be optimal for exercise, when, and the "when" is the key. And I think a lot of people live in the landscape of feeling like there's something broken inside them because they can't focus or they can't-

Samer Hattar:

It's subconscious, remember, it's all subconscious, these effects. And you're absolutely right. Now, honestly, joking aside about age, I really agree with you that I think part of the reason I'm continuing to be able to do this, that I really think about it and I make sure that I keep everything aligned and that actually helps me a lot. I don't suffer in sleep. I don't suffer in waking up. I never use a timer to wake up. I mean, people say, "Aren't you scared, like, you have to give a lecture at eight or 7:30?" Honestly, I was like, there is no way I'm going to go beyond that. Just even if I try, I can't sleep beyond 6:00 a.m. in my regular times. It's just, it's not going to happen; by 4:30 my eyes are wide awake and I'm in bed. It's just system is so aligned, it works.

Andrew Huberman:

A lot of times people will say, "How come I go to sleep, I fall asleep fine, but then I wake up at three or four in the morning and can't fall back asleep?" Is it possible that those people were supposed to go to bed at 8:00 p.m.?

Samer Hattar:

It's possible. I mean, it is possible. It is also possible that sometimes people will wake up and go back to sleep. But yeah, I mean it is possible, or it's possible that their clock is completely misaligned, that they are getting maybe a naptime at night when they are supposed, and then they possibly feel so sleepy in the day. So there all these are possible combinations.

Andrew Huberman:

Well, that's an interesting idea I hadn't considered. So that what they think is their sleep, their body is so out of whack with the light dark cycle that it's actually a nap.

Samer Hattar:

A nap. Or the weaker part of the sleep. I mean, you see this in when you travel to different time zones before you adjust, you go to sleep really well, but two hours later you're fully up. Two hours. If you were so tired and this is your regular sleep, there's no way you're going to wake up in two hours. So then you feel very sleepy later in the day, or something like that. So it depends of how your whole system is aligned to the environment.

Andrew Huberman:

That's a very interesting idea. I think that's going to resonate with a lot of people. I wake up every morning around three or four, I generally use the bathroom and then I fall back asleep very, very deeply. Doesn't seem to disrupt my daytime wakefulness. And I think a lot of people obsess over that waking up and worry there's something wrong.

Samer Hattar:

Absolutely.

Andrew Huberman:

Provided they can go back to sleep, it's okay.

Samer Hattar:

Exactly. If you can go use the bathroom, go back to sleep, that should not be a problem. Maybe some people when they go to use the bathroom, they use very bright light and then they get an alerting signal. So if you, maybe that could be as simple as that. That affects you. Maybe when you wake up, you put tons of light or you start reading your iPad. So there's all these combination that we still don't know about, that could be affecting their sleep wake rhythms and their sleep maintenance.

Andrew Huberman:

Do you use melatonin? Do you take melatonin?

Samer Hattar:

I don't need it, to be honest. In my case, there is no reason to use it because I could guarantee you that by maybe eight o'clock, my melatonin has already started to go up and by the time I sleep, my melatonin is very high because I don't use a lot of lights after sunset.

Andrew Huberman:

And light inhibits melatonin.

Samer Hattar:

Lights really blocks melatonin level.

Andrew Huberman:

You hear this myth that the pineal gland calcifies as we get older; is that, do you know anything about that?

Samer Hattar:

I mean, I've heard about that, but I don't know what does, I mean there's not very clear evidence that affects the sleep. I don't know much about it, to be honest.

Andrew Huberman:

Yeah, the evidence that I've seen is that, yes, there's some calcification around the pineal, just because of where it sits in the brain. It's close to some bony structures. But I don't think there's any evidence that it has negative effects

Samer Hattar:

I mean, if you still have, you could measure melatonin and that should tell you if it has negative, it's such an easy thing to do.

Andrew Huberman:

I think this is more of an Internet wellness thing that-

Samer Hattar:

I think that's possible.

Andrew Huberman:

got outside the cage.

Samer Hattar:

I think you're absolutely right. Yeah.

Andrew Huberman:

It sounds terrible. Calcification of the thing, right?

Samer Hattar:

Like the hard thing, right?

Andrew Huberman:

Yeah, exactly. Let's talk about seasonality a little bit. I learned, and I don't know if this is still true, but that most suicides occur in April, in the spring. I think there's a poem that says April is the cruelest month. I think is the poem begins. Are there data that suicides are more frequent at particular times of year? And if so, is the spring that time of year?

Samer Hattar:

Yeah, I mean a lot of people talk about this, and one of the hypothesis is that the winter month, that are very bad for mood, make people not wanting to do anything, and they get into such deep level of depression that when the sun comes up, they get actually the energy to act on their depression, which sounds really terrible and it is terrible.

Andrew Huberman:

That's terrible.

Samer Hattar:

So that's the idea that the lack of light throughout the winter cause them to go into such depression that they don't feel like doing anything. Then when the light comes in with rigor in the spring, it gives them that, after all the depression they suffer, it gives them that push to take that sad final act, I guess.

Andrew Huberman:

What other seasonal effects have been demonstrated in humans?

Samer Hattar:

Yeah, I mean I think in humans, it's not very clear because we don't think about seasonality. But if you start thinking about us, I think we go through major seasonal changes. I really do. I think our eating pattern change across the year. I could tell you that, me thinking about this, there is a clear changes that happens to me across the year. But for animals, this is really essential. Because for animals, they have to time their mating behavior with when they deliver their progeny in the most abundant amount of food. And artificial light is causing major disruption because if you change the way these animals are receiving the light information, they either start mating much earlier or much later, and their numbers dwindle and they get into the dangers of really completely getting eliminated or extinct.

Andrew Huberman:

Well, human birthrates are definitely going down. I mean in the U.S. in particular.

Samer Hattar:

Some areas, not others.

Andrew Huberman:

Not others right. But are there other effects of seasonality on humans that you're aware of?

Samer Hattar:

Honestly, you could see it perfectly I think, in Scandinavia. I mean you could talk to people who live in-

Andrew Huberman:

I'm sure they get seasonal depression.

Samer Hattar:

What, seasonal depression is one, but actually when you start asking them questions, they tell you in the winter they barely could wake up. They barely have the energy before even depression. Even people who don't get seasonal depression, they'll tell you our energy level is lower, our ability to go to work is not the same. And in the summer, most people actually sleep very little. They tell you, we really can, we feel like we are manic. We have all this energy. And not in a negative way, in a funny way. But if you want to sleep, we have to put these curtain. I think in these situations you could really appreciate the seasonality of a humans. I think we kind of destroyed our seasonality because we don't get exposed to that much natural light. We have all this artificial light. But I think honestly, one of the things that is going to happen if they follow your recommendations about giving light at the same time, giving food, giving exercise.

Andrew Huberman:

Wait, let's be clear, those are your recommendations. I'm just, just fair attribution.

Samer Hattar:

What I'm saying is that this is going to cause them to also experience some changes across the season because now they going to see the sun differently. If you are going to go out in the morning, in the summer, you're going to get the much brighter ... that's why I don't like the change in time. I know people think, "Oh, because you're biased," because I think-

Andrew Huberman:

Wait, wait, wait, wait. Sorry. The change now you're talking about daylight savings?

Samer Hattar:

Daylight savings. It's such a bad idea because it disrupts that rhythm that you are having. Because I think your body, if you keep that rhythm, you will see the whole seasonality. And I look at it from a different aspect than other people. It really, and people say, I'm biased because I'm a morning person. And it may be true, but there's situation-

Andrew Huberman:

Secret conspiracy about morning people.

Samer Hattar:

But is, if you think about it, Andrew, there is a situation where you are getting light perfectly well, and then all of a sudden they delayed by one hour because, and then even though it's the summer, your body now, if you're still not adjusting, think, "Oh wait, what happened? What kind of happened?"

Andrew Huberman:

Well, I'm glad you're bringing this up because I always thought, what's the big deal? One hour, right? One hour shift. Spring forward, fall back.

Samer Hattar:

It's so hard to adjust one hour, actually.

Andrew Huberman:

But this goes back to the beginning of our discussion. It's not just one hour.

Samer Hattar:

Right.

Andrew Huberman:

Because it's one hour across that one day. But there's this cumulative effect on the clock and these three elements of your tripartite model.

Samer Hattar:

Exactly.

Andrew Huberman:

The homeostatic sleep, and the light direct effects on mood.

Samer Hattar:

And when it's so close, it's sometimes hard to figure out how to adjust it perfectly because we are already sleep-deprived in our society. And then you shift it by, so it all accumulates and it has no benefit.

Andrew Huberman:

Well you work at a major government organization, National Institute of Mental Health.

Samer Hattar:

Yeah.

Andrew Huberman:

Why don't we campaign for-

Samer Hattar:

Honestly, I have no idea. I mean it makes no sense.

Andrew Huberman:

No, I'm saying why don't we go campaign?

Samer Hattar:

Yeah, I would love to, I mean it makes no sense to have the summer light goes up at 9:00 p.m. the light goes down where I live in Baltimore at 9:00 p.m., and then all of a sudden when you really want to see the light longer in the day, you now shift the other way. And now it goes all of a sudden at 6:00 p.m. Why do you do these drastic changes? Let it blend across the whole season. Yes, later, earlier at night, but it's at least consistent. It goes in a very consistent manner. I just don't understand why they do this. It makes no sense.

Andrew Huberman:

Well, I think that the reason they do it is because they don't understand the biology.

Samer Hattar:

Exactly.

Andrew Huberman:

Because one hour seems trivial-

Samer Hattar:

It's not.

Andrew Huberman:

Unless you understand the repercussions of that one-hour shift. Because what's also clear now based on what you're saying, is that that one-hour shift is taking you out of alignment with the natural light dark cycle in exactly the wrong direction.

Samer Hattar:

It's pushing people to get even later in the summer when light is going to push you later anyway, it doesn't make sense. You put it beautifully, I just rambled and this is-

Andrew Huberman:

No, no, you made it clear.

Samer Hattar:

I mean it's like, literally, it made you, it made people who are having problem, having an advanced sleep rhythm because they are delayed. Now you give them this hour to make them even more delayed, you push them even later in the day-night cycle. It just doesn't make sense. At all.

Andrew Huberman:

I think 2022 should be the year that we abolish daylight savings.

Samer Hattar:

Ah man, that would be the day for me, honestly.

Andrew Huberman:

Well also, if it has a positive effect on the, what is essentially an epidemic of mental health issues and other issues related to improper interactions with light, that I think is a well worthwhile cause and-

Samer Hattar:

Absolutely. Absolutely.

Andrew Huberman:

And we can explore. So for once we're going to fight with another group.

Samer Hattar:

Common.

Andrew Huberman:

A common battle as opposed to with one another.

Samer Hattar:

I mean, the circadian people, honestly, to give them credit, have been trying for years to abolish daylight savings.

Andrew Huberman:

The problem is they all go to sleep at 9:00 p.m. and wake up at 4:00 a.m. So we never see them.

Samer Hattar:

That's right.

Andrew Huberman:

No, the circadian community has done an amazing job of figuring out what we need.

Samer Hattar:

Right.

Andrew Huberman:

And then the challenge of course, is making sure that people get what they need, and making sure that at a societal level we're not vaulting ourself into the wrong direction.

Samer Hattar:

And the biggest problem is that the late-waking people, they think that really, and I'm going to try to put it in a better way now, they think, "Oh, because you're a morning person, you want to see the sun early, so you want me to suffer it dropping late." But that's not the case. Because what happens is when they shift it back after the daylight saving, now they're going to make you suffer really badly because now it's going to be earlier.

Andrew Huberman:

In the fall.

Samer Hattar:

In the fall when there's not enough light if they keep it the same way. So to try to convince them that actually this, at the end, causes more trouble when you need the light for your late schedule in the fall, when they shift it back. Then they say keep it daylight saving all the time. And that has been proven, that is very bad. People have done studies that literally two areas close to each others and areas that were the whole year on daylight saving has much more problems even in cancer rates and depression. So you don't want to do that. So that's what, trying to convince people that you need to prevent that switch, and you don't need daylight saving at all. That's where the problem happens.

Andrew Huberman:

Interesting. I had not thought about that, but yes, you late risers that in the fall when that's, you fall back, as they say, spring forward, fall back, you dial back the clock. It's really compounding the problem that already exists.

Samer Hattar:

Exactly, and it's really nice if you think keep it consistent; in the spring you get the long, when you get the equinox and then the days start going up, and then even in the summer start going down, and then the fall you get the other equinox and go back. So it's very symmetrical. It goes into short day, longer, long, long, longer, and then short day again. But now you're getting these bumps in both sides of the spring and fall. Why would you do that? Something that is beautifully symmetrical, beautifully smooth. You're putting bumps into it.

Andrew Huberman:

Well, and we ... not just beautiful because it's there, but evolved. I mean essentially this is the system we evolved in for hundreds of thousands of years.

Samer Hattar:

This is the seasonality. Even apart from the exact equator. Every part of the earth has seasonality.

Andrew Huberman:

I want to briefly touch on something which is individual and genetic variation in sensitivity to light. So not chronotype, but first of all, a very basic question. Do people with light eyes, light-colored eyes, are they more sensitive to light than people with darker-pigmented eyes?

Samer Hattar:

I mean, honestly, it makes sense they'll be more, because if you think of my dark pupil, it's blocking more light. So if you have light pupil, yes, for vision, it may not be very obvious, but for something that is measuring the amount of light, you're getting more light than me. So you probably need less light to be effective as somebody who's darker. And that maybe could explain why sometimes lighter people say, "I don't want to go into very bright conditions," because it's really bright.

Andrew Huberman:

Yeah, I can't even be at a cafe with one of these reflective tables, like a metal table, unless I have very dark sunglasses on.

Samer Hattar:

Exactly.

Andrew Huberman:

So bright, it's painful for me.

Samer Hattar:

Right.

Andrew Huberman:

Whereas some people like you, we've sat outside and have meals in here like, fine. I assumed it was kind of Jordanian toughness versus-

Samer Hattar:

No, it's really the pupil blocks more light. So I think it is possible that it's as simple as the pupil blocking more light can have sensitivity. But your question is also goes deeper. Are there more sensitivity differences? And my understanding would be, I would think that it may be, depends on how effective your cells are in responding to light, how healthy your ipRGCs are, but there's not many studies to show that. What is really clear that is happening is that patients with bipolar, they seem to have different sensitivities to light. So it seems that at least people who have psychological changes, they may have differences to the sensitivity of light.

Andrew Huberman:

Are those differences in a particular direction?

Samer Hattar:

I don't remember the exact direction.

Andrew Huberman:

We'll have to, we can look it up.

Samer Hattar:

Yeah. Yeah.

Andrew Huberman:

And people have heard me say this ad nauseam to the point where they actually roll their eyes, but these are the only two pieces of brain, I'm pointing to my eyes, folks, that are outside the cranial vault. They are two pieces of brain that it basically inform the brain about whether or not to be alert or asleep.

Samer Hattar:

Absolutely.

Andrew Huberman:

But you can imagine that those two little pieces of brain that we call eyes would have genetic variations. Of course eye color is genetically modular, is that determined, that there would be genetic variations based on whether or not your ancestry evolved near the equator or further from the equator? Right, I mean, you see more blue eyes in Scandinavia than you do near the equator.

Samer Hattar:

Absolutely. I mean, it's the lack of light that said you need less inhibition because there's not enough light, right, so that's the idea of the change in color. So yeah, I totally agree with you. I mean, I think this is an area that will be studied later and will be empirically determined. The problem we have in this field right now, which I think is the biggest problem, is we don't have a way to measure the ipRGC sensitivities in humans. So we still, like it's easy to measure your root function, if you go to an optometrist, they measure all the details, right? Contrast detection.

Andrew Huberman:

You look at the chart, you look at the list.

Samer Hattar:

Exactly.

Andrew Huberman:

Spelling chart, you look at the letters at the DMV. Yeah.

Samer Hattar:

But for the nonsubconscious, we still don't have a good measuring systems to figure out, what is Andrew's sensitivity, what is Samer's sensitivity, what is this person's sensitivity? And I think we are starting to work on something like that to hopefully develop these techniques. But till we develop them, it's going to be very hard to figure out if there is a sensitivity difference, how do they relate? And on men and woman, dark and light and all that, normal versus psychologically ... on effect and stuff like that.

Andrew Huberman:

Fascinating. And every time you talk, I learn so much. It's like in the best way, the best sense of the term, it's a waterfall of knowledge.

Andrew Huberman:

As a final question, I have a question about sensitivity of a whole other kind. And that's the sensitivity to spicy food. Now, the reason I'm asking this question, what seemingly out of the blue is that I made the mistake once of having Samer cook for me. And I said, "Not too spicy." And he said, "Okay, not too spicy." He actually said, "Okay, not too spicy." And it almost killed me. It was like two or three days. So you know a lot about biology outside the visual system, light, etcetera. You've been around a while. Are there known genetic or inherited, of any kind, sensitivities to spicy food, to things like red peppers and capsicum? Because what you call mild, my friend, almost put me into the hospital.

Samer Hattar:

I think this is similar to you swimming in the ocean, and I need to get developed the pain tolerance.

Andrew Huberman:

True, true. I like cold water swims and Samer's not a fan. But that's going to change, it's adaptable. That's going to change.

Samer Hattar:

Adaptable. That's my belief. Before I met Rejji I was like you. And once I started eating a lot of spicy food, I lost touch of how spicy my food is. So I nearly killed you, Andrew, and I apologize for that.

Andrew Huberman:

I forgive you. So basically what you're saying is that marriage toughened you up.

Samer Hattar:

Toughened me up, exactly.

Andrew Huberman:

Maybe that's, maybe that's the solution.

Samer Hattar:

That's what you need. Yeah.

Andrew Huberman:

Samer, this has been an amazing march through the importance of light, not just for regulating sleep and wakefulness, but also for food timing, the interactions with mood, the interactions with exercise. I'm certain that people are going to start thinking about how to change their relationship with light as a way to anchor everything that they do and that's important to their health. And I just, on behalf of all of them, and just directly from me as your friend and as a colleague for many years now, I just want to say thank you for the incredible work you're doing and for sharing it with us.

Samer Hattar:

Thank you so much. And actually now thinking about all of this and you said I should write a book, I should write a book and call it "The Tripartite Model." I think that would put all these components together, would be very interesting to do at some point.

Andrew Huberman:

You should write a book, you should write, they'll probably try and change the title to like, "Food, Mood, and You," or something because, but you can put in little print "the tripartite model" or whatever. But regardless of what it's called, you absolutely should write a book. And so if you'd like Samer to write a book, or if you'd like to learn more about him, let's talk a little bit about where people can find you. Your laboratory's at the National Institutes of Mental Health, he's head of the chronobiology unit, all these things as I've mentioned earlier. But you are active on Twitter and Instagram.

Samer Hattar:

Right.

Andrew Huberman:

So what is your Twitter handle?

Samer Hattar:

It's @SamerHattar.

Andrew Huberman:

And we will provide a link for that in the show notes.

Samer Hattar:

Sorry, at the, yes, at the Twitter @SamerHattar. And I think the same for Instagram. Yeah actually.

Andrew Huberman:

And Samer has been coaxed on to Instagram, so he does post from time to time. Mostly pictures of food that is incredibly spicy; but also information about chronobiology. He comes on for an Instagram live every once in a while with me. And so definitely give him a follow there and on Twitter. And I'm sure that he'll be happy to answer questions and entertain any and all discussions about chronobiology.

Samer Hattar:

Absolutely. Yeah, and light. Yeah.

Andrew Huberman:

Great. Thank you, Samer.

Samer Hattar:

Awesome. Thank you, Andrew.

Andrew Huberman:

Thank you for joining me for my conversation with Dr. Samer Hattar. I hope you found it as interesting and informative as I did. If you're enjoying this podcast and/or learning from it, please subscribe to our YouTube channel. In addition, please leave us comments and feedback in the comment section on YouTube. A great thing to do there would be to make suggestions about future topics you'd like us to cover, or future guests you'd like me to host on the Huberman Lab podcast. In addition, please subscribe to our podcast on Apple and Spotify. And on Apple, you can leave us up to a five-star review. Please also check out the sponsors that we mentioned at the beginning of the podcast. That's a terrific way to support us.

Andrew Huberman:

For those of you that are interested in supporting scientific research, you can support the research in my laboratory on stress, on sleep, and human performance and other related topics by going to hubermanlab.stanford.edu/giving; and there you can make a tax deductible donation at any level that you like. If you're not already following us on Instagram, please follow us @hubermanlab on Instagram and also on Twitter. Both those places I teach neuroscience and offer information that's not always covered on the Huberman Lab podcast. And last but certainly not least, thank you for your interest in science.

PART 4 OF 4 ENDS [02:10:36]

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