Essentials: Timing Light for Better Sleep, Energy & Mood | Dr. Samer Hattar

0:00Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science -based tools for mental health, physical health, and performance. 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. Samur Hattar as my guest on the Huberman Lab podcast. And now my conversation with Dr. Samur Hattar. Sam, thanks for sitting down with me. My pleasure. You are best known in scientific circles for your work on how light impacts mood, learning, feeding, hunger, sleep, and these sorts of topics.

0:41So maybe you could just weigh us into what the relationship is between light and these things like mood and hunger, etc. 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 sun rise, the sun set. So that's your conscious perception of light. But light has a completely different aspect that is independent of conscious vision. 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 dn is day.

1:25So 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 circu - How does that rhythm show up in the tissues of our body? 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.

2:03The most obvious for you is your sleep wake cycle. You sleep and you're awake and sleep at 24 hour rhythms. The period length of the sleep rhythm on average is 24 .2 hours. So you'll be drifting point two hours every day out of the solar day if you don't get the sunlight. So the sunlight adjusts that approximate data on exact day. So now your behavior is adjusted to the light dark environment or the solar thing. 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.

2:45For example, what's the relevance? I mean, why should we care about that short difference? So let's do the math. If you shift out, point two 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.

3:20What is the machinery that allows that to happen and how does that machinery work? Yeah, so we know, 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. 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 off. And they change it in a way to an electrical signal that allows us to build the image of the environment in our cortices.

4:04However, people have found, including me, with the work of David Burson and Ignatius Proventio, 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 words are only relay rodent 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 messed 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 adjusts all the clocks in our bodies to the central brain clock that allows them to entrain to the 24 hour light dark cycle.

4:54So these are cells that connect the eye of the brain that behave like photoreceptors. Essentially. I think it's worth mentioning now that people who are patterned vision blind, so people who cannot see but have eyes, many of them still have these cells, these melanopsin intrinsically photosensitive cells, and can essentially match or in train as we say onto the light dark cycle. In fact, they possibly have no problems in circadian photorentrainment. They'll have a normal sleep week cycle, but they're totally blind. But they are totally image blind. And what's really interesting is that, and this story I heard from Chuck Seisler, 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.

5:36And doctors used to think, oh, that 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 dox cycle, and are having cyclical jet lags when their clock shifts through the light dox cycle. That's really interesting. And I hear from a number of blind people, 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 absolutely their schedule.

6:11Absolutely. What is the proper way to interact with light in the first part of the day? Honestly, I think the easiest thing is waking up. Get as much light as you can. To your eyes. Yeah, it's really nice. Your system is primed. If you're in train, it's primed to get light. The sun should be out. Even when it's cloudy, you're going to get enough intensity to help you adjust your cycle to the day -night cycle. These are general rules of thumb, but I don't do recommend people go outside. So if you do it daily, I would say 15 minutes. If you don't do it daily, you may want to increase it. You do it more, it doesn't hurt.

6:44And I'll tell you, if you're sensitive, don't, 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. OK. And if, for some reason, one finds himself 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? 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 a humans in artificial conditions, the circadian system is very sensitive to light.

7:24But in reality, in the real environment, light also is affecting other aspects that are independent of the setting of the circadian base maker. 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 yeah, I mean, if you're honestly, if you're that far north and you're in the winter and you want to make sure you don't use these light boxes, I would suggest that personally. Okay, so I think we've nailed down that first part of the day.

8:00Basically, it's 10 to 30 minutes depending on how bright it is. And trying to do that as often as possible to give the system a regularity. 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, you know, stay longer if you want, but if you're in a hurry and you want to do other stuff, that's a great trick. So you might want to compensate with some extra time if you missed it a year too. I've heard you say before it's entirely possible to get severely jet lag without traveling.

8:32Absolutely. Simply by staying in, being on your phone too much, not getting the sunlight. And you saw this during the pandemic, a lot of people mentioned that their sleep -wake cycles 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 late, waking up late, and then you're using very bright light to late at night, your body is going to shift and now your day is going to start instead of like really when the sun comes up let's say at six o 'clock in the morning it's going to, your day is going to start at 11 o 'clock in the morning that's what your body is 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 is completely different timing.

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12:03That's roka .com and enter the code Huberman to save 20 % off your first order. Again, that's roka .com and enter the code Huberman at checkout. 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, you know, to bet around 10, 30 up around seven 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.

12:44So there is great data on this and there is a couple of things that complicate this. The first is the people who usually are late. What do you mean people that wake up late and go to sleep late and wake up late? They have an overwhelmingly higher level of depression because human notice that people who go to sleep early and wake up early, they do better in life. They notice that. They just perform better. They perform better. 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. We discriminate against late rise.

13:16We, in a way, we discriminate. 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 like 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 erhythm, 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. And so you're just gonna be late. 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.

14:05So what should people do in the afternoon slash evening time in terms of their light viewing behavior? I mean, the best thing to do is to let the natural light creep in 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, you know, 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. You do keep your home quite dim to dark at night. I am an extreme, but I measured it for myself, and I asked Raysie, my wife, if she's okay with it, She also liked the dimness both of us can see well in dim conditions, but I think you have to measure it for yourself.

14:52You 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. You know, 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 on circadian clock. and below 10 locks of thread light literally doesn't affect sleep at all. So there are ways to do it. I've seen you check your phone after dark once or twice and you did it by sort of putting your phone away from you, right? It actually makes sense that you know if you shine a flashlight in your eye it's much brighter than you shine the flashlight on the left.

15:36So if you let's look on the side, most of the lights are gonna go this way and you're on the same thing. And even Even when I check sometimes, I check it so fast and switch it off so fast. So 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. 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.

16:16So 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. Bingo. Even if we're sleeping and waking up at the appropriate time. 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're 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.

17:03So the SCN that I told you about earlier, the place where the central pacemaker is the one that received direct input from the retina through the IPRGC's to adjust your circadian clock is not the area that receives the light input for mood regulation. It's a completely different brain region and what's really amazing this region also received direct input from the IPRGC's but projects to areas in the brain that are known to regulate mood including the the eventual medial 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, like 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.

18:00How does that finding informed daily protocols for you or for other people? So that's why we came up with the Tri -Partyate 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 things, they thought only of the environmental But now if you put them all together, you get with this tri -partate 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.

18:43So 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, which is basically the longer you're awake the more you want to be asleep. So that's your homeostatic driver. We've talked about the circadian influence of sleep and the fact that light dark cycle affect the circadian system, which eventually affect 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 other, then your sleep is going to suffer.

19:24So you have to think of the three together to have a beautiful sleep wake cycle. 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 directs of direct, excuse me, effects of light on appetite and feeding behavior. So, for somebody who's interested in affecting their eating behavior, how should they use light in order to adjust their eating behavior? Right. So now that I've told you about all these interactions between the different inputs to the circadian clock, just you think about it as an engineer.

20:09What 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 clock in your system? 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 you your clock, your clock is going to be better. So regular meal times. Regular meal times that fit your circadian clock. So, 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.

20:53I'm eating at regular time. It is amazing. You would be not hungry, let's say, 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. No, the desire to eat is mainly driven by these these ques, these hormone ques that are very exquisitely timed to sleep -wake cycle, but also to light. Exactly. How regular are you, or do you recommend people be about meal times? Are we talking about down to the minute? Absolutely. All right. Plus, so 12 noon is my normal lunch, let's say, plus or minus half an hour.

21:37Okay. So eat around between 11, 30 and 12, 30. If that's the time and it depends if you also do multiple meals. Remember three meals, that's a decision that somebody came up with. I don't know why nowadays people are fewer people are doing that. I think given our friends such in pandas work. Right. I mean, so you could have two meals. You could have very multiples meals that are distributed across your active time. 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. Work as long as they don't eat early in the morning.

22:11That's just you have to work with your schedule with your active schedule But we're talking about really is finding your ideal sleep schedule exactly and finding your ideal eating schedule Exactly and understanding how those two things interact and you know the nice thing as you said finding them out It's gonna help you to understand how they interact because we know from the tripod It's more that they are all interconnected and for each person they're gonna be interconnected differently 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.

22:53But 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 accompanied the other syndromes, you know, 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? I mean, honestly, this is my moochum. This is the thing that I think people, because it's some, I say, don't take a pill, take a photon. And not, I mean, you take pills.

23:33It'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 to, as such, 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. And you can't focus. And you can't focus. We 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, that less.

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25:26Right now, AG1 is giving away an AG1 welcome kit that includes five free travel packs and a free bottle of vitamin D3K2. Again, go to drinkag1 .com slash huberman to claim the special welcome kit of five free travel packs and a free bottle of vitamin D3K2. Let's talk about jet lag. What are the two or three things that people can do to adjust their schedule quickly? Like, let's say, fall classes are starting. You start a new job where you have a baby or a puppy or whatever. What is the best way to shift the clock quickly? So it's very simple as we've talked yesterday. So imagine you're in the outside with no environmental, with no industrial light.

26:06If you, if your body thinks you're 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 that mean? That makes you want to go to sleep later. Yes, it delays your clock. So later in the night, later in your night And actually it just happens that the humans you get a temperature in the deer later in the night temperature in your body After that light start advancing your clock.