Dr. Rhonda Patrick: Kind of on the same lines of this technology thing, but shifting gears more to light, circadian rhythm.

Dr. Andrew Huberman: I mean, this is my favorite topic.

Dr. Rhonda Patrick: Yeah, perhaps your favorite.

Dr. Andrew Huberman: I am obsessed. Yeah.

Dr. Rhonda Patrick: You know, I spend a lot of time at my computer, as do you and many people, and we're all, you know, we spend a lot of time indoors working on our laptops or computers, whatever. And I've heard you talk about something very interesting, which is this low angle, low-solar-angle viewing. And I'd love to have you elaborate on that, because I've always heard, and Satchin Panda was the first to really kind of get me interested in this topic. Our mutual friend, a wonderful chronobiologist, talking about early morning bright light exposure and how important it is for resetting our circadian rhythm, which for people listening, is our 24-hour clock. And everything is on this cycle, as you know more than I do about our metabolism, getting sleepy, our wakefulness, as you mentioned, our arousal, all this stuff. But I would love to know about this low-solar-angle light and how that ties into our circadian rhythm.

Dr. Andrew Huberman: Yeah. So just real quick overview of some very simple biology. Lining the back of your two eyes like a pie crust is your neural retina. These are the neurons that transmit information about the amount and quality of light in our environment to the brain. And then the brain does various things with it. There's a pathway directly from the eyes to the hypothalamus. There's a collection of neurons there called the suprachiasmatic nucleus that dictate our master circadian rhythms that essentially cause all the other cells of our body to be on a similar schedule or control the clocks within all the other cells of our body.

There's a pathway from our neural retinas, of course, to areas of the thalamus, which is essentially a relay station up to the visual cortex for conscious perception of things like color, shape, and edges and things like that. And this system is the main system by which we know where we are in space – vision – in physical space and time. Now, the time part is a little bit more mysterious to most people, but the way it works is the following. Obviously, the sun rises and the sun sets, and our bodies, our internal milieu, need to know where we are in time within the course of a day and longer within the course of a year as well.

We can talk about circannual rhythms in a bit, but there's a special category of neuron called the retinal ganglion cell, which is the cell that actually passes electrical information into the brain. And that cell has a bunch of different types. Some of them respond to edges, to colors, et cetera. But there's a specific type called the intrinsically photosensitive melanopsin retinal ganglion cell. A real mouthful that Satchin Panda, Samer Hattar, Iggy Provencio, David Berson, and others characterized in the early two thousands and for the subsequent years and still characterizing that is a neuron that's not as concerned with the shapes of things or the colors of things, although we'll talk about color in a moment, but rather how bright it is in a given environment.

And it is those cells and the activation of those cells that so-called sets our circadian clock so that we have elevated daytime mood, focus and alertness and that we fall asleep at night and stay asleep. Okay, so low-solar-angle sunlight turns out to be the optimal stimulus for these cells. What do I mean by low-solar-angle? I mean when the sun is low in the sky. So that's twice a day. It's in the morning and in the evening. Low solar angle sunlight, even on cloudy days, okay, even on overcast days, is distinctly different for this system than when the sun is overhead. Why? Okay, so we have in humans…we are trichromats. Unless we're red-green color blind, which is like one in 80 males, I think, we are trichromats.

We have what is sometimes called a blue cone, a green cone, and a red cone. But that really means that they absorb short-wavelength, medium-wavelength, or long-wavelength light. And from that we generate this incredible thing in our brain, which is trichromacy, the ability to see the difference between reds and greens and grays and purples. It's incredible. A mantis shrimp can see far more of those things, but we can see a lot of different color variation based on the absorption of those different wavelengths of light. The intrinsically photosensitive ganglion cells have their own pigment within them. They don't need input from these cones, but they get it and they use it. This is important.

So these cells are brightness detectors such that if you shine a really bright light on your eyes, let's say in the middle of the day, you walk outside in San Diego, Los Angeles, even overcast day like before we came in here today, really bright, tons of photon energy coming in, far brighter than even under these bright artificial lights. Here, even though here it looks really bright. If we were to measure this, the environment we're in now is probably, I don't know, 1500 to 2000 lux. Outdoors is probably 10,000 to, what, 50,000 lux. You know, it's just a wild difference. And again, that's even behind cloud cover. The middle of the day constitutes what's called the circadian dead zone, meaning bright light at that time is known to improve mood. Provided you do not burn, light on the skin may also have effects.

Maybe we talk about sunburn and sunscreen. Maybe we don't avoid that third rail. By the way, I use sunscreen. The right one, as does Rhonda, despite what you might read or hear about on the Internet. We both said it. We both use sunscreen and we just use the right ones and avoid the wrong ones. The light in the middle of the day will improve mood by activating these melanopsin cells. It will improve alertness. On the skin, there's evidence that it can improve the output of certain hormones like testosterone and estrogen. It can improve feelings of well-being. Study out of Israel a few years ago in Cell Press. But that light in the middle of the day, if you see the sun, don't stare at the sun, but if you see it, it looks like white and blue light, right?

All wavelengths essentially coming at you, full spectrum. In the morning, when the sun is low in the sky, you'll notice that there are blues and there are yellows and oranges, maybe even reds if it's a beautiful desert sunrise. And in the evening, of course, the sunset has all that richness of the long wavelength light, orange, red, et cetera, and blue. And it turns out that the cells that set your circadian clock, these melanopsin intrinsically photosensitive ganglion cells, yes, they respond to bright light, very high intensities of light, such as at midday, or from a maybe a sunlight simulator of just blue light in a home environment if you purchase a so called sad lamp.

But the optimal stimulus is that low-solar-angle sunlight in the morning especially, and in the evening, because those cones, and in particular the short-wavelength-responsive cones, aka blue light, and the longer wavelength, the reds, the orange, they converge in terms of driving the activation of those cells, those melanopsin cells, and they activate those cells robustly early in the day. Meaning when you see contrast between blue and orange or blue and red, which is characteristic of low-solar-angle sunlight, you are driving the activation of those intrinsically photosensitive ganglion cells the most, and you are sending the primordial, evolutionarily conserved, robust signal to your brain: The day is starting.

You're going to activate a huge number of different endocrine, neural, and other systems, immune functions in the body. Now, what this translates to is, even if it's overcast, get out as soon as the sun is up. Sorry, I should restate that. Even if it's overcast, as close to waking as possible, get some sunlight in your eyes. Now, notice I said sunlight. You don't have to see the sun as a physical object. Get the light in your eyes. Early day sunlight is going to be most valuable for setting your circadian rhythm. Now, what's interesting is that all species that we are aware of, like dogs, for instance, they're not trichromats, they're dichromats, but they have a short wavelength cone and a long wavelength cone.

Look at a dog in the morning or in the afternoon, and they will look in the direction of the sun. Birds have the pineal that can get light through the skull. So, slightly different, but most all species have some. Excuse me. All species have a dedicated system in the eye and brain to extract the specific qualities of light that are present at early in the day, low-solar-angle sunlight, and again in the evening, low-solar-angle sunlight to convert that into neural and hormone signals that the brain can understand. Put very simply, get outside for five minutes or so in the morning, maybe 10 minutes if it's overcast. Don't wear sunglasses for this. Don't stare at the sun. Eyeglasses and contacts are fine. Don't try and do it through a window. That's not going to work.

Too much is filtered out. And just look in the direction of the sun, the general direction, and you will improve daytime mood, focus and alertness. And it sets a timer for your nighttime sleep. Now, people say, well, I wake up before the sun comes out. What can I do? I always just say, well, listen, unless you have powers I'm not aware of, you got to wait. If you don't have access to sunlight, for whatever reason, for about $100, I don't have any relationship to any of these companies. You can get a 10,000-lux light panel, and you can make your coffee in front of that. It's not quite as good as the yellow blue, orange blue contrast system that's going to come from low-solar-angle sunlight, but it's going to be better than nothing. Now, there's a diabolical twist in all of this.

And then there's a solution also based on low-solar-angle sunlight. The diabolical twist is that early in the day and throughout the day, bright artificial lights are not sufficient for all the good stuff that you want from light. You either need a sunlight simulator or ideally you just get outside for a bit in the morning. After, say, 16 hours of being awake or so, however, it only takes a small amount of bright light to quash the amount of melatonin that's present and to disrupt your nighttime sleep. So you need a lot of light early and throughout the day, but don't get sunburned and don't damage your eyes. And you want a minimal amount of light at night.

In fact, I've vastly improved my transition into sleep by, I'm not talking about red light panels, but just buying some red light bulbs. There are a couple of companies that make these. You can look for them inexpensively. And just going to amber or red lights before sleep for about half an hour, it's known to be to prevent some cortisol increase that can come from bright lights of the blue variety. Some people will just use blue blockers and I have no objection to that. Now, what do you do if you're going to be under bright lights at night? Viewing evening light can partially offset the negative effects of bright light later at night.

And this was shown in a really nice paper where they looked at the degree of melatonin suppression to bright light at night, depending on whether or not people had seen some bright light in that study designed to mimic sunlight in the evening, for I believe it was somewhere between 10 and 30 minutes in the evening. Now, not everyone has time to watch a sunset in the evening, but just getting outside, popping the sunglasses off while you're walking to your car after work, is going to partially offset some of the negative effects of artificial lights at night. And now we could get into a whole description about what's actually happening with low-solar-angle sunlight, and I'm happy to do that.

But suffice to say that the contrast between these oranges and blues, or yellows and blues or reds and blues that are occurring when the sun is relatively low in the sky, you don't actually have to see it crossing the horizon, but if you do, great relatively low in the sky, it's that contrast at about 19 hertz, believe it or not, that's the optimal stimulation for these cells. And there is one company I don't have an affiliation called Two O Life, that has developed a bulb that mimics this. It's actually built by some absolutely spectacular circadian biologists up at the University of Washington. The bulb, unfortunately for me, is a little bit cumbersome because it involves an app, and hopefully they'll make an app free version. But it flickers at 19 hertz between blue and orange.

Blue and orange is designed to mimic the sunrise and sunset. If you're, like, geeking out on light technology, you can do that. But I think there's still some improvements that need to be made. And I'm saying this specifically so they'll make those improvements, because I do like the technology. It's the only one that I'm aware of that's grounded in the logic of how the biology actually is organized with this contrast between long and short wavelength light. But all this is to say, get morning sunlight in your eyes, try and get it again in the evening, great during the day, but don't burn. And at night, try and dim the lights as much as you can, meaning as is reasonable for whatever activities.

And don't sweat it if you don't get bright light in your eyes or sunlight early in the day. One, this is a slow integrating system, but after about two or three days, you'll notice that things like your sleep will start to drift later, your morning energy will drift later. There's also a really interesting effect of cortisol, where bright light exposure early in the day increases the total amount of cortisol by about 50 percent. People hear cortisol and they go, oh, I don't want elevated cortisol. You want your cortisol elevated early in the day, and then you want to taper off end of day. Spikes or increases in late day cortisol are associated with depression and anxiety. Work from our psychiatry department at Stanford has shown that and others have shown that.

So you want that big amplitude and then cruising down out of that cortisol release early in the day, and bright light is one way to do it. That cortisol increase will provide some important activation of certain immune system components, of alertness, of focus. We don't want to treat cortisol as the enemy. It's just about timing and amount, right?

Dr. Rhonda Patrick: You mentioned even five minutes being enough, like early morning bright light exposure, and it's like, is it an hour and a half? How long is this low angle in the morning? How long is the low angle?

Dr. Andrew Huberman: Yeah, probably it depends on the time of year, of course, and location where probably until about, you know, 10 a.m. or so, you know, just if I had to put a, you know, a rough number out there. So if you're waking up at nine, just get outside, if you wake up at six, get outside if you can catch the sunrise. Amazing. I mean, that's the ticket. But most of us are not doing that or not, because we're not waking up early enough, necessarily, but we get up. And if you're in an apartment, can you get to a place where you can see the sunrise across the horizon? But look, if it's combined with a walk, some hydration, some caffeine, and maybe even social time or time with your dog, even better. There's no reason why you can't combine these things.

Dr. Rhonda Patrick: And so also the cortisol one, is that like, how much light was, do you remember how much light was needed in the morning?

Dr. Andrew Huberman: It was quite a bit, yeah. And they used artificial light because it was a laboratory situation, but it was designed to mimic sunlight. I have to go look it up. I'm sorry. I don't recall.

Dr. Rhonda Patrick: Hours?

Dr. Andrew Huberman: I don't think it was hours. I think it was on the order of minutes. I'd be surprised if it was more than an hour. If you get in front of one of these 10,000-lux light panels, and I have one, I bought it on Amazon. It sits on our shelf in the kitchen. So I'm making coffee or something. It's right there. Right in front of my supplements, actually. So I'm there, I'm doling out my supplements and there it is. It's about the size of a computer monitor. And after about five, 10 minutes in front of that thing, you kind of want to get away from it. It's really bright. And some people get a little bit too much activation if they're in front of it for too long. And then, of course, at night, you don't want to be anywhere near that thing. You want it off.

I have one in my gym as well. So if I go into my gym, the lights in my house aren't particularly bright. I'll turn that thing on. And so I'm getting a lot of photons, but of course, nothing beats sunlight. Nothing beats sunlight. And if you get a morning walk in the direction of the sun in the morning, as the sun is rising, then you've done something right in life.

Dr. Rhonda Patrick: I mean, or if you just want to go outside and drink your coffee out on your, you know, porch or patio or yard, whatever.

Dr. Andrew Huberman: Exactly. Exactly.