The Science & Practice of Perfecting Your Sleep | Dr. Matt Walker

Andrew Huberman 0:00 (music) Welcome to the Huberman Lab Podcast, where we discuss science and science-based tools for everyday life. 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. Matthew Walker as our guest on the Huberman Lab Podcast. Dr. Walker is a professor of neuroscience and psychology at the University of California, Berkeley. There, his laboratory studies sleep. They study why we sleep, what occurs during sleep, such as dreams and why we dream, learning during sleep, as well as the consequences of getting insufficient or poor quality sleep on waking states. Dr. Walker is also the author of the international best-selling book, Why We Sleep. Our discussion today is an absolutely fascinating one for anyone that's interested in sleep, learning, or human performance of any kind. Dr. Walker teaches us how to get better at sleeping. He also discusses naps, whether or not we should or should not nap, whether or not we can compensate for lost sleep, and if so, how to best do that. We discuss behavioral protocols and interactions with light, temperature, supplementation, food, exercise, sex, all the variables that can impact this incredible state of mind and body that we call sleep. During my scientific career, I've read many papers about sleep and attended many seminars about sleep. Yet, my discussion with Dr. Walker today revealed to me more about sleep, sleep science, and how to get better at sleeping than all of those papers and seminars combined. I'm also delighted to share that Dr. Walker has started a podcast. That podcast, entitled The Matt Walker Podcast, releases its first episode this month and is going to teach all about sleep and how to get better at sleeping. So be sure to check out The Matt Walker Podcast on Apple, Spotify, or wherever you listen to podcasts. Before

Andrew Huberman 2:00 we begin, I'd like to mention 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. Our first sponsor is ROKA. ROKA makes sunglasses and eyeglasses that are of the absolutely highest quality. The company was founded by two all-American swimmers from Stanford, and everything about the design of their glasses is with performance in mind. I've spent my career studying the visual system and how it works, and I can tell you that ROKA glasses take into account the science of the visual system, such that whether or not you're wearing them on a very bright day or you walk into a shadowed area, or there's cloud cover, you can still see everything with perfect clarity. That also reflects the fact that the lenses that they use are of the absolute highest optical quality. The other terrific thing about ROKA sunglasses and eyeglasses is that they're designed to be worn in all conditions. You can use them while running, while cycling. Even if you get sweaty, they won't slip off. And they look great. One problem I have with a lot of so-called performance eyeglasses and sunglasses out there is that they look crazy. They make people look like cyborgs. ROKA glasses have a terrific aesthetic. You can wear them to dinner, you can wear them at work, and you can wear them in all sorts of sports activities. If you'd like to try ROKA glasses, you can go to ROKA, that's R-O-K-A, .com and enter the code Huberman to save 20% off your first order. That's ROKA, R-O-K-A, .com and enter the code Huberman at checkout. Today's podcast is also brought to us by InsideTracker. InsideTracker is a personalized nutrition platform that analyzes data from your blood and DNA to help you better understand your body and reach your health goals. I've long been a believer in getting regular blood work done for the simple reason that many of the factors that impact your immediate and long-term health can only be analyzed from a quality blood test. And nowadays, with the advent of DNA tests, you can also get insight into your immediate and long-term health by way of understanding your DNA. One issue with many DNA and blood tests, however, is that you get the numbers back about metabolic factors, hormones, genes, et cetera, but there's no directive as to what to do with that information. With InsideTracker, they have a very easy to use dashboard, and that dashboard not only gives you your numbers, but it gives you simple directives related to nutrition, supplementation, exercise, and other lifestyle factors that allow you to move those numbers into the ranges that are right for you and your health goals. If you'd like to try InsideTracker, you can go to insidetracker.com/huberman, and if you do that, you'll get 25% off any of InsideTracker's plans. Just use the code Huberman at checkout. Today's episode is also brought to us by Belcampo. Belcampo is a regenerative farm in Northern California that raises organic, grass-fed, and finished certified humane meats. I don't eat a lot of meat. I eat meat about once a day. But when I do, I make sure that it's high quality and both humanely and sustainably raised. Conventionally raised animals are confined to feedlots and eat a diet of inflammatory grains, but Belcampo's animals graze on open pastures and seasonal grasses, resulting in meat that's higher in nutrients and healthy fats. And I've talked many times before on this podcast about how getting sufficient levels of omega-3s is very important for metabolic health, hormone health, mood, essentially all aspects of one's health. Belcampo meats have high levels of omega-3s because of the grasses they feed on. The way Belcampo raises its animals isn't just better for our health, it also has a positive impact on the environment. They practice regenerative agriculture, which means that their meat is climate positive and carbon negative, meaning it's good for you and it's good for the environment. You can order Belcampo's sustainably raised meats to be delivered to you using my code Huberman by going to belcampo.com/huberman, and if you do that, you'll get 20% off your first order. I'm a big fan of their keto meatballs. I also really

Andrew Huberman 6:00 like their boneless rib eyes. I eat those pretty much once a day. Again, that's Huberman for the code, and it's belcampo.com/huberman for 20% off.... your order. And now my discussion with Dr. Matt Walker. Great to finally meet you in person.

Matt Walker 6:15 Wonderful to connect, um, I mean, it's been too long, but I suspect it would have been a shorter time before we'd met lest the pandemic-

Andrew Huberman 6:23 Yeah.

Matt Walker 6:24 ... but, um, thank you for coming up here.

Andrew Huberman 6:25 No, thank you. Yeah, I'm delighted that we're finally sitting down face-to-face. I've been tracking your work both in the internet sphere, and I read your book and loved it, and also from the perspective of science. You actually came to Stanford couple of years ago and gave a, uh, a lecture, uh, for Brain Mind, uh-

Matt Walker 6:43 Oh, yeah. Yeah, yeah, yeah.

Andrew Huberman 6:45 And, um, there, of course, uh, you talked about sleep and its utility and its challenges and how to, uh, and how to conquer it, so to speak. Um, let's start off very basic. What is sleep?

Matt Walker 6:59 Sleep is probably the single most effective thing you can do to reset your brain and body health. So that's a functional answer-

Andrew Huberman 7:07 Mm-hmm.

Matt Walker 7:07 ... in terms of, you know, what is sleep in terms of its benefits. Sleep as a process, though, is an incredibly complex physiological ballet. And if you were to recognize or see what happens to your brain and your body at night during sleep, you would be blown away. And the paradox is that most of us, and I would think this too, you know, if I wasn't a sleep scientist, we go to bed, we lose consciousness for seven to nine hours, and then we sort of wake up in the morning and we generally feel better. And in some ways, that denies the physiological and biological beauty of sleep. So upstairs in your brain when you're going through these different stages of sleep, the, the changes in brain wave activity are far more dramatic than those that we see when we're awake. And we can speak about deep sleep and what happens there. REM sleep is a fascinating time, which is another stage of sleep often called dream sleep, which is rapid eye movement sleep. That stage of sleep, some parts of your brain are up to 30% more active than when you're awake. So again, it's kind of violating this idea that our mind is dormant and our body is just simply quiescent and, and resting. So I would happy to just sort of double click on either one of those and also what changes in the body as well, but it is an intense evolutionary adaptive benefit, um, and system. That said though, I, I would almost push back against, uh, an evolved system when we think about the question of sleep and what sleep is. Our assumption has always been that we evolved to sleep, and I've actually questioned that, and I have no way to get in a time capsule and go back and prove this, but what if we started off sleeping and it was from sleep that wakefulness emerged?

Andrew Huberman 9:05 Mm-hmm.

Matt Walker 9:05 Why do we assume that it's the other way around? And I think there's probably some really good evidence that sleep may have been the proto-state, that it was the basic fundamental living state, and when we became awake, as it were, we always had to return to sleep. You know, in some ways, at that point, sleep was the price that we paid for wakefulness, and that's another way of describing what sleep is. But again, I think it sort of denies that the active state of sleep, it's not a passive state of sleep either. Um, and then finally you can say what, what is sleep across different species? And in us human beings and in all mammalian species and avian species as well, sleep is broadly separated into these two main types, and we've got non-rapid eye movement sleep on the one hand and then we've got rapid eye movement sleep on the other. And we can speak about how they unfold across a night and their architecture because it's not just intellectually interesting from the perspective of what sleep is, it's also practically impactful for our daily lives, and I'd love to sort of go down that route too, but you navigate. You tell me.

Andrew Huberman 10:18 Yeah, no-

Matt Walker 10:18 I can-

Andrew Huberman 10:19 Let's definitely go down

Andrew Huberman 10:20 that route. So, um, you mentioned how active the brain is during certain phases of sleep. When I was coming up in science, REM sleep, rapid eye movement sleep, was referred to as paradoxical sleep.

Matt Walker 10:32 Yeah.

Andrew Huberman 10:32 Is that still a good way to think about it? Paradoxical because the brain is so active and yet we are essentially paralyzed, correct?

Matt Walker 10:38 Yeah, it really-

Andrew Huberman 10:39 Good.

Matt Walker 10:39 ... is a paradox, and where that came from was simply the brain wave recordings-

Andrew Huberman 10:44 Mm-hmm.

Matt Walker 10:45 ... that if all I'm measuring about you is your brain wave activity, it's very difficult for me sitting outside of the sleep laboratory room to figure out are you awake or are you in REM sleep? Because those two patterns of brain activity are so close to one another, you can't discriminate between them. Yet the paradox is that when you are awake, I go in there and you're sort of sitting up, you're clearly conscious and awake, but yet when you go into REM sleep, you are completely paralyzed, and th- that's one of the... I, I think that's part of the paradox, but the paradox really just comes down to two dramatically different conscious states, yet brain activity is dramatically more similar than different, and the way I can figure out which of the two you are in is by measuring two other signals, the activity from your eyes and the activity from your muscles. So when we're awake, we will occasionally have these blinks and we'll have sort of saccades, but during REM sleep, you have these really bizarre horizontal shuttling eye movements that occur and that's where the name comes from, rapid eye movement sleep.

Andrew Huberman 11:58 Are they always horizontal?

Matt Walker 12:00 Mostly they are horizontal.

Andrew Huberman 12:02 That's interesting.

Matt Walker 12:02 And that's one of the ways that we can differentiate them from other waking eye movement activity 'cause it's not always l- it can be sometimes horizontal, but it can also have diagonal and also vertical in that plane.But then the muscle activity is the real dead giveaway. Just before you enter REM sleep, your brain stem, which is where the dynamics of non-REM and REM are essentially played out and then expressed upstairs in the cortex and downstairs in the body, um, when we go into REM sleep and just a few seconds before that happens, the brain stem sends a signal all the way down the spinal cord, and it communicates with what are called the alpha motor neurons in the spinal cord, which control voluntary skeletal muscles, and it's a signal of paralysis. And when you go into dream sleep, you are locked into a physical incarceration of your own body.

Andrew Huberman 12:59 Amazing.

Matt Walker 13:00 Uh, you know, why, why would Mother Nature do such a thing? And it's in some ways very simple. The brain paralyzes the body so that the mind can dream safely. Because think about how quickly we would have all been popped out of the gene pool, you know, if I think I'm, you know, one of the best skydivers who can just simply fly, and I've had sometimes those dreams too, you know, and I get up on my apartment window and I leap out-

Andrew Huberman 13:27 Mm-hmm. You're done.

Matt Walker 13:28 ... you're done-

Andrew Huberman 13:29 Yeah.

Matt Walker 13:29 ... you know?

Andrew Huberman 13:30 Yeah.

Matt Walker 13:30 So that's one of the sort of, that's part of the paradox of REM sleep, both its brain activity similarity despite the behavioral state being so different, and this bizarre lockdown of the, the sort of brain, of the body itself. Now, of course, the involuntary muscles thankfully aren't, um, paralyzed, so you keep breathing, your heart keeps beating.

Andrew Huberman 13:52 Is this why men have erections during REM sleep and women have vaginal lubrication during sleep?

Matt Walker 13:58 That's one of the reasons. Part of the other reason, though, there is because of the autonomic activity. So there is a nervous, a part of our nervous system called the autonomic nervous system-

Andrew Huberman 14:08 Mm-hmm.

Matt Walker 14:08 ... and it controls many of the automatic behaviors, and some of those are aspects of our reproductive facilities. During REM sleep, what we later discovered is that you go through these bizarre what we call autonomic storms, which sounds dramatic, but it actually is when you measure them, that you'll go through periods where your heart rate decelerates and drops and your blood pressure goes down, and then utterly randomly, your heart rate accelerates dramatically, and what we call the fight or flight branch of the autonomic nervous system, or the sympathetic nervous system, badly named 'cause it's anything but sympathetic, it's very aggravating (laughs) , um, that all of a sudden fires up, and then it shuts down again. And it's not in any regular way, and it's when you get those autonomic storms you get very activated from a physiological perspective, that you can have these erections and you have vaginal discharge, et cetera.

Andrew Huberman 15:04 But you're totally paralyzed?

Matt Walker 15:05 But you are still paralyzed.

Andrew Huberman 15:07 Wow.

Matt Walker 15:07 There are only, um, two voluntary scoli- uh, two voluntary muscle groups that are spurred from the paralysis. Bizarre. One, your extraocular muscles-

Andrew Huberman 15:20 Mm-hmm.

Matt Walker 15:20 ... because if they were paralyzed, you wouldn't be able to have rapid eye movements.

Andrew Huberman 15:25 Mm-hmm, mm-hmm.

Matt Walker 15:25 And the other that we later discovered was the inner ear muscle. And we've got no good understanding as to why those two muscle groups are spurred from the paralysis. It may have something to do with cranial nerve, but I, I, I don't think it's that. I think it's perhaps something more sensory related. Some people have argued that the reason the eyeballs are spurred from the paralysis is because if your eyeballs are left for long periods of time inactive, you may get things such as oxygen sort of issues in the, um, aqueous or vitreous humor-

Andrew Huberman 16:00 Mm-hmm.

Matt Walker 16:00 ... and so the eyeballs have to keep moving in some ways-

Andrew Huberman 16:02 Yeah, the drainage systems of the anterior eye are, are made to require movement, that's-

Matt Walker 16:06 Exactly, yeah.

Andrew Huberman 16:07 People with glaucoma have deficits in, in drainage through the anterior chamber. But there I'm speculating. I'm also speculating when I ask this, um,

Andrew Huberman 16:17 I would imagine that there are states in waking that also resemble slow wave sleep, or rather that-

Matt Walker 16:23 Hmm.

Andrew Huberman 16:23 ... there are states, that slow wave sleep also resembles waking states. You've beautifully illustrated how REM sleep can mimic some of the more active brain states that we achieve in waking. What sort of waking state that I might have experienced, or experience on a daily basis, might look similar to slow wave sleep, non-REM sleep, if any?

Matt Walker 16:43 Uh, it's a genius way of thinking about it, turns the tables, I love it. Um, we almost never see anything like the, the true ultra slow waves of deep non-REM sleep. So, um, we spoke about these two stages, non-REM and REM. Um, non-REM is further subdivided into four separate stages-

Andrew Huberman 17:02 Mm-hmm.

Matt Walker 17:03 ... um, stages one through four, increasing in their depth of sleep. So stages three and four, that's what we typically call deep non-REM sleep. Stages one and two, light non-REM.

Andrew Huberman 17:11 So maybe take me through the arc of a night, just so that, um-

Matt Walker 17:14 Yeah, yeah.

Andrew Huberman 17:14 ... so I, I put my head down, uh, well, for you, what, what time do you normally go to sleep?

Matt Walker 17:18 So I'm usually sort of around about a 10:30 PM guy, and usually I'll naturally wake up sort of a little bit before 7:00, sometimes before 6:45 or 7:00. I have an alarm set for, um, 7:04, um, AM, um-

Andrew Huberman 17:34 You heard it here, folks.

Matt Walker 17:35 (laughs)

Andrew Huberman 17:35 Matt Walker does use an alarm clock.

Matt Walker 17:37 I rarely, rarely, I'm usually sort of-

Andrew Huberman 17:39 He doesn't recommend it, but he does use it.

Matt Walker 17:41 Yeah, I usually sort of-

Andrew Huberman 17:41 You're, you're human after all.

Matt Walker 17:42 Oh, I am so human, um, and, and I've had my sleep issues, and I'd love to speak about that too, but, um, it's only just, you know, in the event that-

Andrew Huberman 17:52 Mm-hmm.

Matt Walker 17:52 ... um, you know, 'cause I like to keep regularity too. You've got to keep those-

Andrew Huberman 17:55 Sure.

Matt Walker 17:55 ... two things in balance. And 7:04 just because, you know, why not be idiosyncratic? Uh, I don't know-

Andrew Huberman 18:01 Love it.

Matt Walker 18:01 ... why we always set things, uh, on these, uh, hard numbers. So yep, so when you and I-

Andrew Huberman 18:06 So, so you go to sleep around 10:30.

Matt Walker 18:08 Yup.

Andrew Huberman 18:08 So using you as an example, um, because I imagine a number of people go to sleep at different times, but 10:30 is about when I go to sleep, 11:00 is for me, but, um, so you go to sleep at 10:30. So for that first...... um, let's say, three hours of sleep. Wh- what does the architecture of that sleep look like as compared to the last three hours of your sleep, uh, before morning?

Matt Walker 18:28 Yeah. So, I should note that that sort of, you know, 10:30 to 7:00, that's just based on my chronotype and my-

Andrew Huberman 18:35 Mm-hmm.

Matt Walker 18:35 ... preferential. It's different for different people. I'm not-

Andrew Huberman 18:37 Sure.

Matt Walker 18:37 ... suggesting that that's the perfect sweet spot for humanity's-

Andrew Huberman 18:41 Mm-hmm.

Matt Walker 18:41 ... sleep. It's just my, uh, natural-

Andrew Huberman 18:42 But I imagine-

Matt Walker 18:43 ... sweet spot.

Andrew Huberman 18:43 ... most people probably go to sleep somewhere between 10:00 and PM and midnight, and most-

Matt Walker 18:50 It's somewhere between, like, 9:00 and midnight.

Andrew Huberman 18:50 ... probably wake up between 5:00 AM and 7:00 AM or, or 5:30 and 7:30?

Matt Walker 18:55 Yeah, yeah.

Andrew Huberman 18:55 Yeah, okay.

Matt Walker 18:56 Um, at least in, if you look at sort of first world nations, that's-

Andrew Huberman 18:59 Mm-hmm.

Matt Walker 19:00 ... that's a typical-

Andrew Huberman 19:00 Mm-hmm.

Matt Walker 19:00 ... sleep profile. Um, so when I first fall asleep, I'll go into the light stages of non-REM sleep, stages one and two of non-REM, and then I'll start to descend down into the deeper stages of non-REM sleep. So after about maybe 20 minutes, I'm starting to head down into stage three-

Andrew Huberman 19:18 Mm-hmm.

Matt Walker 19:19 ... non-REM and then into stage four non-REM sleep. And as I'm starting to fall asleep, as I've cast off from the, uh, usually with me, murky waters of wakefulness, um, and I'm in the shallows of sleep, stages one and two, my heart rate starts to drop a little bit and then my brain wave pattern activity starts to slow down. Normally, when I'm awake, it's going up and down maybe 20, 30, 40, 50 times a second. Um, as I'm going into light non-REM sleep, it will slow down to maybe 15, 20, and then really starts to slow down-

Andrew Huberman 19:54 Mm-hmm.

Matt Walker 19:54 ... down to about sort of 10 or eight cycles per second-

Andrew Huberman 19:58 Mm-hmm.

Matt Walker 19:58 ... eight cycle waves per second. Then as I'm starting to move into, um, stages three and four non-REM sleep, several remarkable things happen. All of a sudden, my heart rate really does start to drop. Oh, and I'll come back to temperature. I'm going to write temperature down 'cause I always forget these things. Um, now I'm solidly in the foothills of middle age. Um, so as I'm starting to go into those deeper stages of non-REM sleep, all of a sudden hundreds of thousands of cells in my cortex all decide to fire together and then they all go silent together.

Andrew Huberman 20:35 Hmm.

Matt Walker 20:36 And it's this remarkable physiological coordination of the likes that we just don't see at, during any other brain state.

Andrew Huberman 20:45 That's really interesting-

Matt Walker 20:45 It's-

Andrew Huberman 20:45 Having recorded from the brains of, of animals and a little bit from humans, I don't think I've ever seen the entire cortex or even entire regions of cortex light up like that.

Matt Walker 20:54 Yeah.

Andrew Huberman 20:54 Yeah, amazing.

Matt Walker 20:54 It's, it's stunning. It's, it's almost like this beautiful sort of mantra chant.

Andrew Huberman 21:00 Hmm.

Matt Walker 21:00 Um, or this sort of, you know, it's a slow inhale and then a meditative exhale.

Andrew Huberman 21:05 Mm-hmm.

Matt Walker 21:05 Inhale, exhale. And these waves are just enormous in their size.

Andrew Huberman 21:10 And the body is capable of movement at this time? There is no s- paralysis?

Matt Walker 21:14 There is no paralysis, but for-

Andrew Huberman 21:15 Okay.

Matt Walker 21:15 ... the most part, muscle tone has also dropped significantly-

Andrew Huberman 21:19 Interesting.

Matt Walker 21:19 ... at that point. And then you will, or I will then stay there for about another 20 or 30 minutes, so now I'm maybe 60 or 70 minutes into my first sleep cycle, and then I'll start to rise back up, back up into stage two non-REM sleep, and then after about 80 or so minutes, I'll pop up and I'll have a short REM sleep period.

Andrew Huberman 21:41 Mm-hmm.

Matt Walker 21:41 And then back down I go again, down into non-REM, up into REM. And you do that reliably, repeatedly, and I will be doing that, and I do do that every 90 minutes. At least, that's the average for most adults.

Andrew Huberman 21:56 Mm-hmm.

Matt Walker 21:56 It's different in different species. What changes, to your question, is the ratio of non-REM to REM within that 90-minute cycle as you move across the night. And what I mean by this is, in the first half of the night, the majority of those 90-minute cycles are comprised of lots of deep non-REM sleep. That's when I get my stage three and four of deep non-REM sleep. Once I push through to the second half of the night, now that seesaw balance changes-

Andrew Huberman 22:25 Mm-hmm.

Matt Walker 22:25 ... and instead, the majority of those 90-minute cycles are comprised either of this lighter form of non-REM sleep, stage two non-REM sleep, and much more and increasingly more rapid eye movement sleep.

Andrew Huberman 22:38 Mm-hmm.

Matt Walker 22:38 And the implication that I was sort of speaking about pragmatically is, let's say that, um, I have to, and I usually never do early morning flights or red eyes, um, just because I'm a mess if that happens, I'm not suggesting that other people shouldn't-

Andrew Huberman 22:53 I'm suggesting people-

Matt Walker 22:54 ... it's just, just me.

Andrew Huberman 22:54 ... not do that.

Matt Walker 22:55 Um...

Andrew Huberman 22:55 Every time I've taken a red eye or I've done that, two or three days later I get some sort of general feeling of malaise, my brain doesn't work as well. I, I think red eyes should be abolished. I-

Matt Walker 23:05 For the pilots too, I mean, you know, and for the-

Andrew Huberman 23:07 Oh, and we can speak about those, you know, those data-

Matt Walker 23:08 ... and for the, and for the emergency room. I mean, long shifts have been shown to lead to, you know, physician induced, uh, errors that, uh, lead to a lot of fatalities. I'm in there- Yup.

Andrew Huberman 23:17 ... a lot of reasons why staying up too long or being up at the wrong times, if you're not adapted to it, is just terrible, right?

Matt Walker 23:23 Y- The data in all of those cases-

Andrew Huberman 23:24 Yeah.

Matt Walker 23:24 ... you know, and particularly physicians too. There was some recent data looking at suicidality and the rates of suicide in training physicians are, you know, far, far above the norm.

Andrew Huberman 23:35 Mm-hmm.

Matt Walker 23:35 And I don't suspect that, you know, their schedules are helping them. I suspect that sleep is a missing part of that explanatory equation, but-

Andrew Huberman 23:45 I teach medical-

Matt Walker 23:46 ... you know.

Andrew Huberman 23:46 ... students and, and they, they're phenomenal, but they, yeah, they're under extremely challenged conditions. It's, uh-

Matt Walker 23:52 We shouldn't put them under those conditions.

Andrew Huberman 23:53 No, it's not, it's not optimizing performance.

Matt Walker 23:55 It's, it's, you know.

Andrew Huberman 23:55 Um, I have one-

Matt Walker 23:56 But sorry, I was-

Andrew Huberman 23:57 Yeah.

Matt Walker 23:57 Sorry.

Andrew Huberman 23:57 No, no, no. This, this is important, these, um, uh, it's an important

Andrew Huberman 24:00 digression of... I have one question, which is, you're saying that as across the night, a greater percentage of these 90-minute cycles are going to be occupied by REM sleep as you progress through the night. I'm aware that there, uh, based on work that you've done and, and, uh, and from your public education efforts and others, um, that-We have so-called circadian forces, and we have other forces that are driving when we sleep and when we wanna sleep, et cetera. Without going into the details of those, I have a simple question. The experiment is the following. Let's say, God forbid, you are prevented from going to sleep at your normal time-

Matt Walker 24:38 Yeah.

Andrew Huberman 24:38 ... and you stay up for the four hours or five hours that normally you would be in predominantly slow wave sleep.

Matt Walker 24:45 Yeah.

Andrew Huberman 24:46 If, let's say, you finally get to lie down at 3:00 AM, a time when normally your sleep would be occupied mostly by rapid eye movement sleep-

Matt Walker 24:56 Yeah.

Andrew Huberman 24:57 ... will you experience a greater percentage of rapid eye movement sleep because of these so-called circadian forces, meaning that's what's appropriate for that time? Or will your system need to start at the beginning of the race that we're ref-

Matt Walker 25:11 (laughs)

Andrew Huberman 25:11 ... that as I, as I'm referring to it-

Matt Walker 25:12 Yeah.

Andrew Huberman 25:12 ... that we're calling sleep?

Matt Walker 25:14 Yeah.

Andrew Huberman 25:14 If we're, if that's not clear to anybody, basically what I'm asking is if you are forced to skip the slow wave sleep part of the night, will your system leap into rapid eye movement sleep or does it have to start at the beginning and get slow wave sleep first? In other words, does one sleep state drive-

Matt Walker 25:30 Yeah.

Andrew Huberman 25:30 ... the entry to the next sleep state?

Matt Walker 25:32 Great question. So there is some degree of reciprocity between the sleep states, I should note, that when we drive one of those up, we often but not always see a, a change in the other. There are some pharmacologies that have shown an independence to that, and we've also played around with things like temperature. And sometimes you can, you know, nudge one and not seem to upset or perturb the other.

Andrew Huberman 25:58 Mm-hmm.

Matt Walker 25:58 But to your, um, I think lovely point, th- the answer is it's a mix, but it's mostly the latter, meaning you will mostly go into your REM sleep phases and be significantly deficient in your deep sleep. So just because I start my sleep cycle at 3:00 AM rather than at 10:30 PM, it doesn't mean that my brain just says, "Well, I've got a program, and I'm just going to run the program, and the way the program runs is that we always start with a first couple of hours of deep sleep. So we're just gonna begin act number one, scene one." It doesn't do that. Now, I will get some deep sleep to begin with, and part of that is just because of how sleep works based on how long I've been awake. The longer I'm awake, there is a significantly greater pressure for deep sleep. But we actually use exactly what you just described as an experimental technique to selectively deprive people of one of those stages of sleep or the other. So we will do first half of the night deprivation, and then let you sleep the second half, so that means that you will be mostly deep sleep deprived and you will still get mostly all of your REM sleep.

Andrew Huberman 27:15 Mm-hmm.

Matt Walker 27:15 And then we switch it so you only get your first four hours, which means you will mostly get deep non-REM sleep, but you will get almost no REM sleep. So in both of those groups, they've both had four hours of sleep, so the difference between them in terms of an experimental outcome is not the sleep time because they've both slept for the same amount, it's the contribution of those different stages. Now, we actually have more elegant methods for sort of selectively going in there and scooping out different stages of sleep, but that's the way we used to do it old school, was just using this timing difference.

Andrew Huberman 27:49 And who suffers more, those that lack the early phase or those that lack the later phase of the night sleep? In other words, sh- if I have to sleep only four hours for whatever reason, am I better off getting the early part of the night sleep or the l- second half of the night sleep?

Matt Walker 28:05 Depends on what y- the outcome measure is. Eh.

Andrew Huberman 28:07 Um, so that gets right to the differences between slow wave sleep and REM.

Matt Walker 28:11 Right.

Andrew Huberman 28:11 Uh, I was, um, probably misinformed, but my understanding, a very crude understanding I should, I should say before, um-

Matt Walker 28:18 I very much doubt it.

Andrew Huberman 28:19 ... which is-

Matt Walker 28:19 Au contraire with someone like you.

Andrew Huberman 28:21 Was it... Uh, which is, that, that, very nice of you, but the, the, the first part of the night, the slow wave sleep, is restorative to the musculature, to motor learning, and that the dream content tends to be less emotional. The second half of the night being more emotional dreams and sort of the unpairing of the emotional load of our previous day and other experiences. So, in other words, if I were to deprim myself, deprive myself, excuse me, of REM, I would be hyperemotional, not, maybe not as settled with m- the kind of experiences of my life, whereas if I had to deprive myself of slow wave sleep, I would, um, feel a f- a more physical malaise. Is that correct or is that far too simple? And if it is too simple, please, uh, tell me where I'm wrong.

Matt Walker 28:59 No, I think much of that is correct, and it's sort of that plus.

Andrew Huberman 29:04 Mm-hmm.

Matt Walker 29:04 So, for example, during deep non-REM sleep, that's where we get this, it's almost a form of natural blood pressure medication.

Andrew Huberman 29:12 Mm-hmm.

Matt Walker 29:12 And so when I take that away from you, the next day, we're usually going to see autonomic dysfunction, we're usually going to see abnormalities in heart rate, blood pressure. We also know that it's during deep non-REM sleep that there is a certain control of specific hormones. For example, we know that the insulin regulation of sort of metabolism-

Andrew Huberman 29:31 Mm-hmm.

Matt Walker 29:32 ... uh, meaning how will you look from a regulated blood sugar perspective versus dysregulated pre-diabetic look of profile, that's where deep sleep seems to matter. If we selectively deprive you of that, we can see, and-

Andrew Huberman 29:48 Growth hormone?

Matt Walker 29:48 Growth hormone is different actually. So that's a, that's a beautiful demonstration, where growth hormone seems to be more REM sleep dependent, and that's why we can come on to the effects of alcohol, and there was, there's some really impressive, frightening data on, on alcohol and its disruption of, um, of sleep. But then we also know testosterone. You know, peak levels of testosterone happen during REM sleep.

Andrew Huberman 30:11 So the second half of the night, essentially.

Matt Walker 30:12 E- which is the second half-

Andrew Huberman 30:13 Yeah.

Matt Walker 30:13 ... of the night. So, it really just means that the, your profile of mental and physical dysfunction will be different under both of those conditions. Which one would you prefer? I would prefer neither of them, and it really depends on what you're trying to optimize for.

Andrew Huberman 30:32 Mm-hmm.

Matt Walker 30:33 So, it's, it's just so comple- you know, sleep is just so...... pluripotent. You know, it's so physiologically systemic that it's almost impossible not to undergo one of those two things, just deep sleep deprivation or just REM sleep deprivation, and not show a profile that you would really prefer to avoid-

Andrew Huberman 30:55 Mm-hmm.

Matt Walker 30:55 Uh, and that's the, that's the reason from an evolutionary standpoint that we've preserved those stages of sleep. I mean, sleep is just so idiotic, you know, from an evolutionary perspective.

Andrew Huberman 31:07 Or maybe waking is idiotic. (laughs)

Matt Walker 31:08 Oh, waking is ... You know, I ... Well, yeah. I think you-

Andrew Huberman 31:11 Based on your previous, uh, idea that-

Matt Walker 31:12 Yeah, yeah, who have you been talking to?

Andrew Huberman 31:13 (laughs)

Matt Walker 31:13 Yeah, I think that comment is very specific to me. Um, yeah, I am normally, um, a- always an idiot wh- when waking. But I think this, this idea that sleep, you know, is so profoundly detrimental to us, if you were to take it at face value, you know, you're not finding a mate, you're not reproducing, you're not foraging for food, you're not caring for your young, and worst of all, you're vulnerable to predation.

Andrew Huberman 31:39 Mm-hmm.

Matt Walker 31:39 On any one of those grounds, sleep probably should have been selected against, but it wasn't. Sleep has fought its way through heroically-

Andrew Huberman 31:47 Mm-hmm.

Matt Walker 31:47 ... you know, every step along the evolutionary path, and therefore every sleep stage has also survived as best we can tell. What that means is that those are non-negotiable. If Mother Nature had found a way to even just sort of, you know, thin slice some of that sleep from us, there would've been vast, I'm sure, evolutionary benefits, but it looks-

Andrew Huberman 32:13 Mm-hmm.

Matt Walker 32:13 ... as though she hasn't, and I'm usually in favor of her wisdom after 3.6 million years, so,

Matt Walker 32:20 um ...

Andrew Huberman 32:20 Yeah, it's a- it's incredible. I wanna introduce a- another, um, gedankenexperiment, another thought experiment. So in this arc of the night, uh, slow wave sleep predominates, uh, early in the night, and then REM sleep. There's a scenario that many people, including myself, experience on a regular basis which is, they go to sleep, sleeping just fine, three, four hours into it, they wake up.

Matt Walker 32:43 Yeah.

Andrew Huberman 32:43 They wake up for whatever reason, maybe there was a noise, maybe the temperature isn't right. We will certainly talk about sleep hygiene, et cetera. They get up, they go to the restroom, they might flip on the lights, they might not. They'll get back in bed, hopefully they're not picking up their phone and-

Matt Walker 32:59 (laughs)

Andrew Huberman 33:00 ... starting to browse and wake up the brain through various mechanisms, light and cognitive stimulation, et cetera. They go back to sleep. Let's say after about 10, 15 minutes they're able to fall back asleep and then they sleep till their more typical wake time.

Matt Walker 33:12 Yeah.

Andrew Huberman 33:14 How detrimental is that wake up episode or, or, um, event in terms of longevity, learning, et cetera? I would love to sleep the entire night through every night-

Matt Walker 33:27 Yeah.

Andrew Huberman 33:27 ... but most nights I don't, and yet I feel pretty good throughout the day-

Matt Walker 33:32 Yup.

Andrew Huberman 33:32 ... some days better than others.

Matt Walker 33:33 Yeah.

Andrew Huberman 33:33 So if you were to kind of evaluate that waking episode and compare it to sleeping the whole night through, what are your, what are your thoughts on that?

Matt Walker 33:44 So I think if you're waking up sort of frequently as you're describing, um, I would probably get your estate in order because my guess is within the next year you're gonna be, you're gonna be done for. (laughs) No, I'm kidding you. Absolutely kidding you. It is perfectly natural and normal-

Andrew Huberman 34:01 Mm-hmm.

Matt Walker 34:01 ... particularly as we progress with age. You know, children tend to have, um, typically more continuous sleep. Now, it's not that they aren't waking up for brief periods of time, they are, and in fact we all do. When we come out the other end of our sleep cycle at the end of our REM sleep period of the 90-minute cycle, almost everybody wakes up and we make a postural movement.

Andrew Huberman 34:25 Mm-hmm.

Matt Walker 34:25 We turn over because we've been paralyzed for so long and the body will also like to shift its wake position.

Andrew Huberman 34:30 Do we ever look around? Do we ever open our eyes and look around?

Matt Walker 34:34 You ... Some- sometimes people will open their eyes, but usually it's only for a brief period of time and they usually never commit those awakenings to memory.

Andrew Huberman 34:42 Right.

Matt Walker 34:44 Your situation, and it's my situation as well, I usually now at this stage of life I don't sleep through the night, I'll usually have a bathroom, uh, break and then I'll come back. That's perfectly normal. We tend to forget that in sleep science we think of sleep efficiency, so of the total amount of time that you're in bed, how much of that percent time is spent asleep? And we usually look to numbers that are above 85% or more as a healthy sleep efficiency.

Andrew Huberman 35:18 Mm-hmm.

Matt Walker 35:19 So if you were to think about me going to bed and I spend, you know, let's say eight and a quarter, eight and a half hours of time in bed with a normal healthy sleep efficiency, I still may be only sleeping a total of seven and a half hours or seven and three quarter hours, meaning that I'm going to be awake in total, not in one long bout, but I'm going to be awake for upwards of 30 minutes net some time.

Andrew Huberman 35:51 Mm-hmm.

Matt Walker 35:51 Sometimes that can be after a 10 minute, you know, dalliance after having gone to the bathroom and I'm just gradually drifting back off again. Other times it will just be for a couple of minutes, and most of those you don't commit. So I think we need to stop ... We don't need to get too worried about, you know, periods of time awake just because we're not sleeping throughout the night. I would love to do that too, and I remember when I ... That used to happen, and it still happens, you know, occasionally.

Andrew Huberman 36:18 Every once in a while. It feels great when it does happen.

Matt Walker 36:19 And, and it's, it's a lovely thing, but-

Andrew Huberman 36:21 It's a surprise, right?

Matt Walker 36:22 It is now a surprise.

Andrew Huberman 36:23 Like, "Oh my goodness, I slept through the whole night." Yeah.

Matt Walker 36:24 Yeah, it is a surprise.

Andrew Huberman 36:25 Yeah.

Matt Walker 36:25 But for the most part I think we can be more relaxed about that. Where we have to be a bit more attentive though is if you are spending long periods of time not being able to get back to sleep, and usually we define that by saying if it's been 20, 25 minutes, normally that's a time when we would really say, "Okay, let, let's explore this. What's going on? Let's see what's happening." The other thing is if it's happening very frequently, so even if you're, um-... you know, not awake for 25-minute stretches, but you're finding yourself waking up and being consciously aware that you've woken up for maybe six, seven, or eight times throughout the night, and your sleep is very what we call fragmented, the great science of sleep in the past five or 10 years hasn't, has been, yes, quantity is important, but quality is just as important. And you can't have one without the other in terms of a good, beneficial next day outcome. You can't just get four hours of sleep, but brilliant quality of sleep and be unimpaired.

Andrew Huberman 37:33 Right.

Matt Walker 37:33 Nor can you get eight hours of sleep, but have very poor quality of sleep and be unimpaired the next day. So that's why I just sort of want to asterisk this idea of let's not get too worried about waking up and having some time awake, that's perfectly normal and natural, but if it's happening very frequently throughout the night, or those periods of time are long stretches of time, upwards of 25 minutes, then let's look into it.

Andrew Huberman 38:00 Mm-hmm. Well, I can assure you just, um, helped a lot of people, uh, feel better about this waking up episode that I and many other people experience-

Matt Walker 38:10 I, I hope-

Andrew Huberman 38:10 ... um-

Matt Walker 38:10 ... so because I, I, 'cause I think it's really important that we, you know, I think I've been desperately guilty of perhaps, you know, early on being too puritanical about, you know, sleep. And, and I've, I've retrospected and I've tried to explore why this was the case, you know, it was almost sleep or else, dot, dot, dot (laughs) you know?

Andrew Huberman 38:33 Mm-hmm.

Matt Walker 38:33 And at the time when I was starting to write the book, which was back in 2016, you know, sleep was still a neglected stepsister in the health conversation of today. And I could see all of the-

Andrew Huberman 38:45 That has certainly changed.

Matt Walker 38:46 And it's changing-

Andrew Huberman 38:47 Yeah.

Matt Walker 38:47 ... you know, and not because-

Andrew Huberman 38:48 Yeah, it's changed.

Matt Walker 38:48 ... of my efforts, but because-

Andrew Huberman 38:49 No, I would say-

Matt Walker 38:50 ... of all of my colleagues, uh-

Andrew Huberman 38:50 I would say, I, well, I, it's a great, um, that you give a- attribution to your-

Matt Walker 38:55 Right.

Andrew Huberman 38:55 ... other people involved, and of course, it's a big field, but I think, um, you've done a great service by cuing people to the importance of this state, not just for avoiding troublesome outcomes, but also for optimizing their waking state. It's real, you know, I, I view sleep as this period that feels good, but we're not aware of how it feels when we're in it necessarily.

Matt Walker 39:16 Yeah. Yeah.

Andrew Huberman 39:16 Um, it has tremendous benefits when you're doing it well, so to speak, and it has tremendous, um, deficits when, when you, we're not. And I think, I think it was an important thing for you to do, to cue people to this issue. And I would say, mission accomplished, that people are aware of the need for sleep. I think that knowing that waking up in the middle of the night is normal, provided it's not too frequent, is, is great and will also help people who may have been overly concerned about that. I, I do want to use this as an opportunity

Andrew Huberman 39:48 to raise something about the so-called Uberman schedule, not-

Matt Walker 39:53 (laughs)

Andrew Huberman 39:53 ... to be confused with the Huberman-

Matt Walker 39:55 Huberman.

Andrew Huberman 39:55 ... schedule.

Matt Walker 39:56 Yeah.

Andrew Huberman 39:56 Um, fortunately no one, uh, has confused those yet.

Matt Walker 39:59 (laughs)

Andrew Huberman 40:00 Um, the, some years ago there was a discussion about the so-called Uberman schedule, meaning the Superman schedule, so that's Huberman without an H.

Matt Walker 40:08 (laughs)

Andrew Huberman 40:08 Which I have nothing to do with. Um, if you read your Nietzsche, this mi- w- this will have a subtext, but regardless-

Matt Walker 40:14 (laughs)

Andrew Huberman 40:15 ... um, the Uberman schedule, as I understand, is one in which, um, the person elects to sleep in 90-minute bouts spread throughout the day and night-

Matt Walker 40:25 Right.

Andrew Huberman 40:25 ... in an attempt to get more productivity, um, and/or reduce their overall sleep need. There was a paper published recently that explored whether or not this is good or bad for us. Maybe you just, uh, give us the take home message on that.

Matt Walker 40:38 Yeah, so these Uberman-like, uh, schedules, and there's lots of different forms of that, they try to essentially pie chart the 24-hour period into short bouts of sleep with some shorter, or no, well, slightly longer periods of wakefulness, then short bouts of sleep, then wakefulness. It, you know, you're, I sort of made it a, a I think a quip, it's almost like you're sleeping like a baby, you know?

Andrew Huberman 41:04 Mm-hmm.

Matt Walker 41:04 'Cause that's the way that babies-

Andrew Huberman 41:05 Yeah, nine, in 90-minute naps.

Matt Walker 41:06 ... w- will sleep.

Andrew Huberman 41:07 Yeah.

Matt Walker 41:07 That they will have, you know, these-

Andrew Huberman 41:08 Yeah.

Matt Walker 41:08 ... brief naps, then they're awake-

Andrew Huberman 41:09 Yeah.

Matt Walker 41:09 ... then they're asleep, then they're awake, and to the chagrin of parents, across the night it's basically the same, they're awake, they're asleep, they're awake, they're asleep. And that's more the, the schedule that these types of protocols have, um, have suggested. And there was a really great comprehensive review that found not only that they weren't necessarily helpful, but they were actually really quite detrimental. And on almost every performance metric, whether it be task performance, whether it be physiological outcome measures, whether it even be the quality of the sleep that they were having when they were trying to get it, all of those were in a downward direction. And it's not surprising-

Andrew Huberman 41:50 Yeah.

Matt Walker 41:50 ... if you look at your, the way that your physiology is programmed, if you look at the way your circadian rhythm is programmed, none of that screams to us that we should be sleeping in that way. Uh-

Andrew Huberman 42:02 Well, I'm chuckling because, uh, we always hear, "Sleep like a baby." This is how babies sleep. And, uh-

Matt Walker 42:06 Right.

Andrew Huberman 42:07 ... I would say, don't sleep like a baby, sleep like an adult.

Matt Walker 42:09 Yeah.

Andrew Huberman 42:10 Be an adult.

Matt Walker 42:10 I mean, it's b-

Andrew Huberman 42:10 Get, get your solid eight hours, yeah.

Matt Walker 42:11 It, it's Billy Crystal's line, he was a, um, you know, a longstanding suffering, uh, insomniac, he says, "I sleep like a baby, I'm awake every 20 minutes." You know, and I think this is another one of those demonstrations that when you fight biology, you normally lose.

Andrew Huberman 42:28 Mm-hmm.

Matt Walker 42:28 And the way you know you've lost is disease, sickness, and impairment.

Andrew Huberman 42:32 Mm-hmm.

Matt Walker 42:32 And I think if you sleep in accordance with the natural biological edict that we've all been given, life tends to be both of a higher quality and a longer duration.

Andrew Huberman 42:44 Yeah, I agree. And along those lines, um, um, as

Andrew Huberman 42:48 a vision scientist I've been very excited by the work on these, uh, non-image forming cells in the eye, the so-called melanopsin cells-

Matt Walker 42:53 Yeah.

Andrew Huberman 42:53 ... that inform the brain about ti- circadian time of day. And I'm a big proponent of people getting, uh, some sunlight, ideally sunlight, but other forms of bright light into their eyes early in the day and when they want to be awake.

Matt Walker 43:06 Yep.

Andrew Huberman 43:06 Essentially during the phase of their 24-hour circadian cycle when temperature is rising, and then starting to get less light in their eyes-... as our temperature is going down in term- later in the day and in the evening. Are there any adjustments to that general theme that you'd like to add or is, um, in any way?

Matt Walker 43:25 No. I think that's exactly what we recommend right now, which is try to get at least 30 to 40 minutes of exposure to some kind of natural daylight. Now, there may be parts of the world where, you know, it's-

Andrew Huberman 43:38 Yeah. You're from-

Matt Walker 43:39 ... it- it's-

Andrew Huberman 43:39 ... you're from a rather cloudy part of the world.

Matt Walker 43:41 I am from, yeah, uh, Liverpool, England.

Andrew Huberman 43:44 Oh.

Matt Walker 43:44 Uh, and, uh, the northwest of England is not known for its, um, beach resorts-

Andrew Huberman 43:49 Mm-hmm.

Matt Walker 43:49 ... and fine weather. Uh, I, I remember I'd sort of... I went back home for a trip when I'd first been out, uh, in California, and I thought, "Why is the sky so low?" You know? (laughs) It was just, you know, constantly out. We joke that in, um, in the UK we usually have nine months of bad weather and then three months of winter, and that- that's your, that's your entire year-

Andrew Huberman 44:14 Oh my gosh.

Matt Walker 44:14 ... of, uh, in terms of a climate. But to come to your point, you're exactly right, try to get that daylight. Now, it can be, you know, working next to a window and you're getting that natural sunlight, but that natural sunlight is, even on a cloudy day in England, is f- usually far more potent than anything that you'll get from indoor lighting despite you thinking sort of from a perception-wise, maybe they're- they're much closer than I would think.

Andrew Huberman 44:40 Yeah. I've been, um... Sorry to interrupt. I've been a-

Matt Walker 44:42 Oh, no.

Andrew Huberman 44:43 ... a big proponent of, there's a- an app called Light Meter which will, it's a free app, uh, I have nothing to do with it, that will allow you to, uh, get a pretty decent measurement of the amount of- of light energy coming toward you. And if you, um, hold it up to a cloudy morning where you don't think it's very bright out, kind of a dismal day, you'll notice that there'll be 1,000, 2,000, even, you know, 5,000 lux, lux just being a measure of brightness, of course. And then you can point the same light meter toward an indoor light that seems very bright and very intense-

Matt Walker 45:10 (laughs)

Andrew Huberman 45:10 ... and it'll say 500 lux.

Matt Walker 45:12 Yes, sir.

Andrew Huberman 45:13 And you realize that the intensity as we gauge it perceptually is not really what the system is receiving, so outdoor light is key. How do you w- w- how do you get this natural stimulation or, um, l- I should just say light stimulation early in the day? What- what is your typical... What does Matt Walker do to get this light stimulation?

Matt Walker 45:31 (laughs) I am no poster child, but, um, usually I will, um, if I'm working out, I usually work out most days, um, and I shopped around and I found a gym that has huge amounts of window exposure facing to the east. This is sound, this is gonna sound so, uh, ridiculous, you know, Matt Walker chooses a gym on the basis of-

Andrew Huberman 45:51 I love it.

Matt Walker 45:51 ... the solar input so he can-

Andrew Huberman 45:53 Well-

Matt Walker 45:53 ... you know, correct his circadian-

Andrew Huberman 45:54 ... there are a lot of criteria for selecting gyms.

Matt Walker 45:56 Uh-

Andrew Huberman 45:56 This one is actually grounded in physiology-

Matt Walker 45:58 (laughs)

Andrew Huberman 45:58 ... and biology and so-

Matt Walker 46:00 And selfishness about my own sleep.

Andrew Huberman 46:02 No, it's great. So you, so you get your exercise and your light stimulation simultaneously.

Matt Walker 46:05 That's right. Yup, yeah, so-

Andrew Huberman 46:06 And so you're stacking cues for wakefulness early in the day?

Matt Walker 46:09 Exactly.

Andrew Huberman 46:10 Mm-hmm.

Matt Walker 46:10 So both exercise and daylight are wonderful cues for circadian rhythm alignment and also circadian rhythm reset each day, and so I will use both exercise... I mean, I am, I'm neither a strong morning type or a strong evening type, and my preference to exercise is probably some time in the middle of the day-

Andrew Huberman 46:31 Mm-hmm.

Matt Walker 46:32 ... uh, probably somewhere around 1:00 A- 1:00 PM. Sorry, not 1:00 AM. Um, but I'm usually working out probably around the sort of seven sort of 45, 8:00 AM time. That's usually when I'll start my workout, and there I'll start with cardio, spin bike facing a window, and luckily for the most part here in California, there's usually sunlight coming through, but it doesn't matter to me because just as you said even when it's a cloudy day that lux coming through of light, the- the intensity is- is splendid. So I would prefer to favor my exercise just because for efficiency too, I want to get also working on the day. Um, I'll try to match my exercise more with my circadian light exposure than I would probably if I'm going to do I really want to crush a workout or do I want to just, you know, make sure it's a good workout? I would prefer to work out, you know, at a different time.

Andrew Huberman 47:32 Mm-hmm.

Matt Walker 47:33 But I like that because of the daylight. And we can speak about exercise timing at some point because there's a lot of discussion around that when is the right exer- time to exercise during sleep and we can sort of bust some myths there too. Um, so I think you're spot on with the suggestion, get some morning daylight, try to get that exposure usually at least 30 to 40 minutes. There was some great work recently coming out in the occupational health domain where they moved workers from offices that were just facing walls and, you know, didn't have any exposure to natural daylight and then they did a time period during that study where they actually were in front of a window and working and they measured their sleep. And their sleep time and their sleep efficiency increased quite dramatically. I'm forgetting the numbers now, but I think the increase in total sleep time was well over 30 minutes and the improvement in sleep efficiency was 5 to 10%. You know, and if you're batting an 80%, you know, sleep efficiency average, w- we're a bit concerned about that, but add 10% to that, now you're in, you know, a great echelon of healthy sleepers-

Andrew Huberman 48:40 Mm-hmm.

Matt Walker 48:40 ... and all you did was just spend some time working in front of windows.

Andrew Huberman 48:44 That's great. And probably, um, folks might want to consider spending a little less time with sunglasses provided they can do that safely-

Matt Walker 48:50 Yup.

Andrew Huberman 48:50 ... you know, driving, et cetera.

Matt Walker 48:51 Yeah.

Andrew Huberman 48:51 You're not alone with your exercise behavior in facing east. So, um, the one and only Tim Ferriss told me recently that his morning routine nowadays consists of jumping rope while facing east to get the sunlight stimulation of- of the eyes.

Matt Walker 49:06 Of it.

Andrew Huberman 49:06 And, um, as, uh, Matt and I both know, it has to be of the eyes, right?

Matt Walker 49:10 Yeah. Yeah. Yeah.

Andrew Huberman 49:11 I mean, these portals are the only way to s- to, um, convey to the rest of the brain and body about the time of day and wakefulness. Um-... a- along

Andrew Huberman 49:20 the lines of wakefulness, I have a number of questions about caffeine.

Matt Walker 49:24 Yeah.

Andrew Huberman 49:24 The dreaded and beloved caffeine.

Matt Walker 49:26 Yeah.

Andrew Huberman 49:26 I love caffeine, but I like it in relatively s- um, restricted periods of time. So, um, I'm a big fan of waking up and, even though I wake up very groggy, allowing my natural wakefulness signals to take hold, meaning I wake up very slowly but I don't drink caffeine right away.

Matt Walker 49:47 Yeah.

Andrew Huberman 49:47 I sort of delay caffeine by a li- a little while, usually 90 minutes to two hours.

Matt Walker 49:53 Okay.

Andrew Huberman 49:53 And that idea came to me on the basis of my understanding of how caffeine and the a- adenosine receptor interact. I have a feeling you're going to pronounce adenosine differently than I do. (laughs)

Matt Walker 50:04 No, no, no, I will go with-

Andrew Huberman 50:05 (laughs)

Matt Walker 50:05 I will go with adenosine.

Andrew Huberman 50:06 I'll, I'll t- try to go with your skeletal instead of skeletal...

Matt Walker 50:09 (laughs)

Andrew Huberman 50:10 ... and synapse in synapse. Um, but-

Matt Walker 50:11 I'll be shedule on schedule.

Andrew Huberman 50:12 There we go. But, um, but to make it really simple for folks, how does caffeine work to make us feel more alert? And does the timing in which we ingest caffeine play an important role in whether or not it works for us or against us? So maybe we just start with h- how, how does caffeine work? Why is it that when I drink mate or coffee, which are my preferred sources of caffeine, do I feel a mental and physical lift?

Matt Walker 50:40 Yeah. So I'm going to suggest counter to what most people would think, drink coffee. (laughs)

Andrew Huberman 50:48 (laughs)

Matt Walker 50:48 Which is-

Andrew Huberman 50:48 Or mate, is mate okay also?

Matt Walker 50:50 Y- yeah, yeah, yeah.

Andrew Huberman 50:50 Or whatever form you enjoy, yeah.

Matt Walker 50:52 We'll, we'll come on to sort of why I suggest that but when it comes to coffee, uh, I would say the dose and the timing makes the poison.

Andrew Huberman 51:02 Mm-hmm.

Matt Walker 51:03 So let's start with how caffeine works. Um, caffeine is in a class of drugs that we call the psychoactive stimulants. So it works through a variety of mechanisms, um, one is a dopamine mechanism. Dopamine we often think of as a reward chemical or, um, but dopamine is also very much an alerting neurochemical as well. And caffeine has some role it seems to play in increasing dopamine, but its principal mode of action we believe, in terms of making me more alert and keeping me awake throughout the day, is on the effects of adenosine. And to explain what adenosine is, from the moment that you and I woke up this morning, this chemical adenosine has been building up in our brain. And the longer that we're awake, the more of that adenosine accumulates.

Andrew Huberman 51:55 Is it, um, may I ask, is it accumulating in neurons, in glia, or in the blood vessels? Where and, and is it also accumulating in my body? Where is this a- adenosine coming from and where is it accumulating?

Matt Walker 52:08 Yeah, so the adenosine here that we're talking about that is creating the sleep pressure is a central brain phenomenon, and it comes from the neurons themselves combusting energy.

Andrew Huberman 52:18 Mm-hmm.

Matt Walker 52:19 And as they're combusting energy, one of the offshoots of that is this chemical adenosine.

Andrew Huberman 52:25 Okay.

Matt Walker 52:26 And so as we're awake throughout the day and our brain is metabolically very active, it's accumulating and building up this adenosine. Now, the, the more adenosine that we have, the sleepier that we will feel. So it really is like a, a sleep pressure is what we call it. Now, it's not a mechanical pressure, don't worry, your head's not going to explode.

Andrew Huberman 52:49 Mm-hmm.

Matt Walker 52:49 It's a chemical pressure, and it's this weight of sleepiness that we feel gradually growing as we get into the evening.

Andrew Huberman 52:57 May, may I just interrupt you-

Matt Walker 52:58 Yeah.

Andrew Huberman 52:58 ... again to just ask, uh, do we know what the circuit mechanism is for that? I mean, not to, um, go too far down the rabbit hole but for the-

Matt Walker 53:06 No, no.

Andrew Huberman 53:06 ... aficionados and for myself, uh, we have brain mechanisms like locus coeruleus that re- release things, uh, brain areas, locus coeruleus just being a brain area of course, that release things that create, that proactively create wakefulness.

Matt Walker 53:19 Yeah.

Andrew Huberman 53:20 So are those neurons shutting down as a consequence of having too much adenosine or are there areas of the brain that promote sleepiness that are then-

Matt Walker 53:30 (laughs)

Andrew Huberman 53:30 ... becoming activated? Because these-

Matt Walker 53:31 Yeah.

Andrew Huberman 53:31 ... you can imagine both things working in parallel.

Matt Walker 53:33 Yeah.

Andrew Huberman 53:33 One or the other would accomplish the same end point.

Matt Walker 53:36 Yeah.

Andrew Huberman 53:36 Yeah.

Matt Walker 53:36 And it's, it's both. And so there are two main receptors for adenosine, the A1 receptor and the A2 receptor, and they have different modes of activating brain cells or inactivating or decreasing their likelihood of firing. And adenosine works in this beautiful, elegant way where it will inhibit and shut down the wake promoting areas of the brain whilst also increasing and dialing up the volume on sleep activating, sleep promoting -

Andrew Huberman 54:09 Biology is so beautiful.

Matt Walker 54:10 Oh, it's fantastic.

Andrew Huberman 54:10 It's always a push pull.

Matt Walker 54:11 Yeah.

Andrew Huberman 54:11 I mean we, and we could have a larger discussion at some point about the, um, everything, seeing dark edges, seeing light edges, uh-

Matt Walker 54:18 Yeah.

Andrew Huberman 54:18 ... our ability to, to smell or to sense pressure on this, everything's a push pull in biology.

Matt Walker 54:22 Oh, it's great, yeah, yep.

Andrew Huberman 54:23 So this is another example where as I am awake longer, adenosine is released in the brain and my wakefulness areas are being actively shut down by that a- adenosine and my sleepiness brain area, so to speak, are being promoted to be more active. Is that correct?

Matt Walker 54:41 That's right, and it's a very progressive process. It's not like a step function where... And sometimes that happens occasionally, b- but it's usually because you've been sort of driving through and as we'll come on to, have caffeine in the system, and then all of a sudden you just hit a wall and it just, you know, engulfs you and you go from a zero to a, the one of sleepiness within a short period of time. Normally-

Andrew Huberman 55:03 What explains the fatigue after a hard conversation? (laughs)

Matt Walker 55:06 (laughs)

Andrew Huberman 55:06 The desire to go to sleep or the desire to go to sleep during a hard conversation?

Matt Walker 55:10 Um, I, that's an interesting one, I think it's usually just based on personality type interactions-

Andrew Huberman 55:15 Yeah, okay.

Matt Walker 55:16 ... and for the most part most-

Andrew Huberman 55:17 Not that I've ever experienced that before but-

Matt Walker 55:18 No, people with you don't but with me they almost-

Andrew Huberman 55:20 Oh, no, no, no, I mean I've experienced-

Matt Walker 55:22 No, no, no, no.

Andrew Huberman 55:22 ... the desire to, to... Some conversations-... I'm halfway through them and I feel like I want to take a nap.

Matt Walker 55:28 Yeah.

Andrew Huberman 55:29 Right? Um-

Matt Walker 55:30 And I would love to look at, you know, people's sleep history. We've sort of seen that time and time again, but, um, and then it could be, you know, with- with folks like me, people just lose the will to live within about five minutes-

Andrew Huberman 55:40 Not-

Matt Walker 55:40 ... of speaking with me. So-

Andrew Huberman 55:41 Not true.

Matt Walker 55:42 ... that's- that's ... I don't get sleep-

Andrew Huberman 55:42 They hear that sleep is important.

Matt Walker 55:44 It's unrelated-

Andrew Huberman 55:44 That's all, so then they ... they ...

Matt Walker 55:45 And that's flattery. That's great. But so the way that then caffeine comes into this, um, equation, as I was saying, it's usually a kind of a linear process, or maybe it's probably closer to an exponential in terms of your subjective feeling of sleepiness. Um, and we haven't really been able to measure that in humans, because normally we ... it's hard to actually, you know, stick something into the brain and be, you know, sucking, siphoning off stuff every couple of minutes as you could do in animal studies and keep asking people every couple of minutes, "How sleepy do you feel? How sleepy?" And track to see if there's a linear rise in, uh, you know, adenosine which then creates an exponential rise in subjective sleepiness or what the dynamics are, but I'm- I'm kind of nerding out. Caffeine comes into play here because caffeine comes into your system and it latches onto those welcome sights of adenosine, the adenosine receptors. But what it doesn't do is latch onto them and activate them, because if it was doing that then it would, you know, in lots of ways it would dial up more sort of sleepiness. It does the opposite. The way that caffeine works is that it comes in, competes with quite sharp elbows with adenosine, competitively, forces them out of the way, hijacks that receptor by latching onto it, but then just essentially blocks it. It doesn't inactivate the receptor, it doesn't activate the receptor. It functionally inactivates it in the sense that it takes it out of the game for adenosine. So it's- it's like someone, you know, coming into a room and you're just about to sit down on the chair and caffeine comes in and just pulls out the chair and you're like, "Well, now I've got nowhere to sit." And caffeine just keeps pulling out the chairs from adenosine, and adenosine, even though it's at the same concentration in your brain, your brain doesn't know that you've been awake for, you know, 10 hours, 16 hours at that point when you've downed a cup of coffee, because all of that adenosine, that's still there, can't communicate to the brain that you've been awake for 16 hours because-

Andrew Huberman 57:59 But it's ... but the adenosine is still in brain circulation.

Matt Walker 58:01 Correct. So it-

Andrew Huberman 58:02 So- so the real question is, what happens when caffeine is dislodged from the adenosine receptor?

Matt Walker 58:06 Unfortunate things happen and that's what we call the caffeine crash, which is caffeine has a half-life and it's metabolized. Um, and-

Andrew Huberman 58:15 Do you recall what the half-life is?

Matt Walker 58:16 Yeah, the half-life is somewhere between five to six hours and the quarter life therefore is somewhere between 10 to 12 hours. It's variable. Different people have different, um, durations of its action, but for the average adult, five to six hours. That variation we understand, it's down to a liver enzyme or a set of liver enzymes, um, of the class that we call the cytochrome P450 enzymes, and there are two ... I think last I- I delved into the data which was pretty recently, there are two gene variants that will dictate the enzymatic speed with which the liver breaks down caffeine and that's why you can have some people who are very sensitive to caffeine and other people who say, you know, "I'm just ... doesn't effect me really that much at all."

Andrew Huberman 59:02 These are the people that have a double espresso after a 9:00 PM dinner and can sleep just fine.

Matt Walker 59:07 Well, and we'll come on to-

Andrew Huberman 59:08 Or at least subjectively they think they're sleeping just fine.

Matt Walker 59:09 Subjectively, yeah, and we- we should speak about that- that assumptive danger too. So then the caffeine is in the system, um, and after some time period it will be inactive in the system. So let's say that, you know, I've been awake for 12 hours now and it's, you know, 8:00 PM and I'm feeling a bit tired but I want to push through and I want to keep working for another couple of hours so I have a cup of coffee. All of a sudden I was feeling tired but I don't feel like I've been awake for 12 hours anymore because with the caffeine in the system, maybe only half of that adenosine is being communicated through the receptor to my brain. 100% of the d- the adenosine is still there, only half of it is allowed to communicate to my brain. So now I think, "Oh, I haven't been awake for 12 hours, I've just been awake for six hours, I feel great." Then after a few hours and the caffeine is starting to come out of my system, not only am I hit with the same levels of adenosine that I had before I'd had the cup of coffee several hours ago, it's that plus all of the adenosine that's been building up during the time that the caffeine has been in my system.

Andrew Huberman 1:00:20 So sort of a- an avalanche of adenosine.

Matt Walker 1:00:22 It is a tsunami wave, yeah.

Andrew Huberman 1:00:24 Well, and I've-

Matt Walker 1:00:24 And that's the caffeine crash.

Andrew Huberman 1:00:25 And, uh, it's interesting because the caffeine crash at, uh, 2:00 in the afternoon when you have work to do is a terrible thing, but what about the person, maybe this person is me in my 20s, who says, "I'm gonna drink caffeine all day long and then I want the crash because at 9:00 or 10:00 PM if I stop drinking caffeine at say 6:00 PM and I crash, then I crash into a- a slumber, a- a deep night of sleep."

Matt Walker 1:00:52 Yeah.

Andrew Huberman 1:00:53 Is that sleep really as deep as I think it is? Because given the half-life of caffeine that you mentioned a few moments ago, I have to imagine that having some of that caffeine circulating in my system might disrupt the depth of sleep or somehow the architecture of sleep in a way that even if I get eight or who knows, even 10 hours of sleep, it might not be as restorative as I would like it to be.

Matt Walker 1:01:17 Yeah.

Andrew Huberman 1:01:17 Yeah.

Matt Walker 1:01:17 And that is the danger, just sort of that, you know, those people that you described who say, and I ... a lot of them will, um, speak with me too, say, "Look, I can have two espressos with dinner and I fall asleep fine and I stay asleep," because usually those are the two phenotypes that we typically see with too much caffeine. I just can't fall asleep as easily as I want to or I fall asleep but I just can't stay asleep. And caffeine can do both of those things quite potently.

Andrew Huberman 1:01:42 How late in the day do you think is-... a- assuming somebody, translate this, folks, if you go to bed early or late, or you have to shift, uh, the hours accordingly. But given, um, somebody who typically go- gets into bed around 10:00, 10:30, and falls asleep around, uh, uh, 11:00, 11:30-

Matt Walker 1:01:57 Yeah.

Andrew Huberman 1:01:58 ... when would you recommend they halt caffeine intake? And these are not, um, strict prescriptives-

Matt Walker 1:02:04 Right.

Andrew Huberman 1:02:04 ... but I think people do benefit from having some, uh, fairly clear guidelines of what might be-

Matt Walker 1:02:09 Yeah, yeah.

Andrew Huberman 1:02:09 ... might work for them. Would you say cut off caffeine by what time of the day?

Matt Walker 1:02:15 I would usually say take your typical bedtime and count back sort of somewhere between 10 to... eight hours is probably getting a little bit close, but take back sort of 10 hours or eight hours of time. That's the time when you should really stop, you know, using caffeine is the suggestion.

Andrew Huberman 1:02:32 Mm-hmm.

Matt Walker 1:02:33 And the reason is because for those people who even just keep drinking up until, you know, the, into the evening, you're right that they can fall asleep fine, maybe they stay asleep, but the depth of their deep sleep is not as deep anymore. And so there are two consequences. The first is that for me t- and it can be up to by 30%. And for me to drop your deep sleep by 30%, I'd have to age you by between 10 to 12 years, or you can just do it every night to yourself-

Andrew Huberman 1:03:01 Wow.

Matt Walker 1:03:01 ... with a couple of espressos. The second is that you then wake up the next morning and you think, "Well, I didn't have problems falling asleep, and I didn't have problems staying asleep. But I don't feel particularly restored by my sleep. So now I'm reaching for three or four cups of coffee the next morning rather than just two or three cups of coffee." And so goes this dependency cycle that you then need your uppers to wake you up in the morning and then sometimes people will use alcohol in the evening to bring them down because they're overly caffeinated. And alcohol, and we can speak about that too, also has very deleterious impacts on your sleep as well. So you're right that it's not just the quantity of your sleep or even difficulties falling or staying asleep, it can also be deep sleep. But here again, I think, you know, I don't want to be frightening people, and I mentioned this before, I think one of the real problems that I, or mistakes that I made, 'cause I didn't, you know, I'd never had much public exposure before the book. Um, and I was so saddened by, you know, the disease and the- the suffering that I was seeing as a consequence of a lack of sleep in our society, and the fact that it wasn't really being discussed very much, I sort of came out, um, you know, a little bit headstrong, more than a little bit headstrong. And I think I was, you know, perhaps too, too much gas pedal and too little, you know, brake as it were. And I don't think that's the right way to approach health message within the public sphere. And I've become much sm- softer in how I think about these things. I have ideas about what the ideal world looks like for sleep, but I also realize that none of us live in this thing called the ideal world.

Andrew Huberman 1:04:51 We certainly don't.

Matt Walker 1:04:52 So, uh, you know, I want to be really mindful of that and I think I've done a really bad job of being sort of too forthright, particularly for people who struggle with sleep. You know, early on when I- I would offer these sort of messages about sleep, I want to be, you know, I want to be veritical when it comes to the science, I want to be faithful to the science, but I also don't want to go out and scare the living daylights out of people, particularly people who are struggling with s- their sleep 'cause it's probably only gonna make matters worse. So I've been beautifully schooled by, um, learning how to be a slightly better public communicator. I'm nowhere near of the standing that, that you are. You're very elegant and it's very intuitive to you. I'm still with training wheels, but I'm getting a little bit better. But I do- I just want to say that when I'm speaking about caffeine 'cause it sounds as though I'm very, um, sort of overt about it. But I will come back to why I say drink coffee, um, but I just wanted to make that point.

Andrew Huberman 1:05:48 Yeah. Well, I appreciate you making that point, and I'm sure our listeners will too. Um, I- I still will, um, stand behind my statement, um, which is that what you've done for the notion that sleep is vital for ha- all aspects of health and for performance, mental, and physical and wakefulness, uh, the message and the, um, the packaging it was contained in and is, has been clearly, clearly net positive. People needed to be cued to this.

Matt Walker 1:06:15 Thank you.

Andrew Huberman 1:06:15 The "I'll sleep when I'm dead" mentality is one that-

Matt Walker 1:06:17 Mm-hmm.

Andrew Huberman 1:06:17 ... I had. It's one that other people have. Um, people in a huge number of vital communities, not just your, your students, but also, um, people... This- the messaging that you provided and continue to provide has positively impacted the first responder community-

Matt Walker 1:06:33 Mm-hmm.

Andrew Huberman 1:06:33 ... the medical community, there's still steps that need to be taken, the military community, and of course, the civilian community. And so I think these adjustments about, yeah, caffeine's okay, just restrict it to the early part of the day if you can most days. Right, exactly. Yeah. I mean, I think the law of averages, it's like the light viewing behavior. Uh, I think it is critical to view sunlight or- or natural, some other form of bright light early in the day, but if you miss a day, it's not that your whole system is going to-

Matt Walker 1:06:58 Exactly.

Andrew Huberman 1:06:58 ... dissolve into a puddle of tears.

Matt Walker 1:07:00 Yeah.

Andrew Huberman 1:07:00 That'll- that'll happen on the second or the third day. No, I'm kidding.

Matt Walker 1:07:03 (laughs)

Andrew Huberman 1:07:03 You get a couple of days. Biology works in averages ex- except with respect to accident or injury.

Matt Walker 1:07:09 Yeah.

Andrew Huberman 1:07:09 A car accident is a car accident, right? You don't g- get to have three of those before the brain damage occurs if the accident's severe enough.

Matt Walker 1:07:16 Yeah.

Andrew Huberman 1:07:16 But with sleep behavior, these, um, homeostatic type behaviors or with food, one chocolate sundae, is it gonna kill you? No.

Matt Walker 1:07:24 Right.

Andrew Huberman 1:07:24 Every night, yeah, it's gonna make you demented and kill you early. We know this. And so I think the- the middle ground is often a hard place to achieve. Um, so I think you've done a phenomenal job.

Matt Walker 1:07:34 Oh,

Andrew Huberman 1:07:34 ... I appreciate you raising these points. And I- and I think, um, it- it's clear that we all need to- that we all can and should do certain things better, including-... being gentle with ourselves from time to time when we deviate from these, uh, these ideal circumstances. Along these lines, I, I do

Andrew Huberman 1:07:54 want to talk about alcohol-

Matt Walker 1:07:55 Yeah.

Andrew Huberman 1:07:55 ... because I think caffeine and alcohol represent the, uh, the kind of two opposite ends of the spectrum. Clearly, there are other stimulants. Um, they're your Adderalls and your, uh, high energy drinks that people uses. But alcohol and caffeine are, are the most commonly consumed-

Matt Walker 1:08:09 Yeah.

Andrew Huberman 1:08:10 ... stimulants and, and sedatives, depressants as they're sometimes called. So, um, what happens when somebody has a glass, uh, th- we always hear a glass or two of wine in the evening or a, or a, uh, a cocktail after dinner-

Matt Walker 1:08:26 Yeah.

Andrew Huberman 1:08:26 ... or before dinner. How does that impact their sleep? And then we'll be sure to circle back in terms of what is reasonable ranges of behavior when it comes to, uh, avoiding alcohol or in- if it's age appropriate, et cetera-

Matt Walker 1:08:41 (laughs)

Andrew Huberman 1:08:41 ... enjoying alcohol.

Matt Walker 1:08:43 Yeah. So alcohol, if we're thinking about classes of drugs, they're in a class of drugs that we call the sedatives, and I think one of the first problems that people often mistake, alcohol is often used as a sleep aid for people who are struggling with sleep when things like over-the-counter remedies, et cetera, or herbal remedies have just not worked out for them, and alcohol, unfortunately, is anything but a sleep aid. The first reason that most people use it is to try and help them fall asleep.

Andrew Huberman 1:09:13 So do- and this process of this event I- that we call falling asleep, I have to imagine is a process-

Matt Walker 1:09:19 It is a process.

Andrew Huberman 1:09:20 ... like everything in biology.

Matt Walker 1:09:21 Yeah.

Andrew Huberman 1:09:21 And that that process involves, in some way t- as we talked about push-pull before, turning off thinking, planning-

Matt Walker 1:09:28 Yep.

Andrew Huberman 1:09:28 ... et cetera, and turning on some sort of relaxation mechanism. I have to imagine that these two things are knobs turning in opposite directions-

Matt Walker 1:09:36 That's right.

Andrew Huberman 1:09:36 ... that gives us this outcome we call falling asleep. Alcohol, it seems, is helpful for some people to turn off their thoughts or their planning.

Matt Walker 1:09:45 Right, yeah.

Andrew Huberman 1:09:45 Is that right?

Matt Walker 1:09:46 Y- y- yes, it is. And so I think, you know, if we look at the pattern of brain activity, if I were to place you inside an MRI scanner where we're looking at the activity of your brain and watch you drifting off, some parts of your brain will become less active, other parts will become more active, and this is the push-pull model. It's inhibition, excitation. But alcohol is quite different in that regard. Alcohol is, because it's a sedative, what it's really doing is trying to essentially knock out your cortex. It's sedating your cortex, and sedation is not sleep, but when we have a couple of drinks in the evening, when we have a couple of nightcaps, we mistake sedation for sleep saying, "Well, I always, when I have a, like a couple of whiskeys or a couple of cocktails, it always helps me fall asleep faster." In truth, what's happening is that you're losing consciousness quicker, but you're not necessarily falling naturalistically asleep any quicker, so that's one of the first sort of things just to keep in mind. The second thing with alcohol is that it fragments your sleep, and we spoke about the quality of your sleep being just as important as the quantity, and alcohol through a variety of mechanisms, uh, some of which are activation of that autonomic nervous system, that fight or flight branch of the nervous system. Alcohol will actually have you waking up many more times throughout the night, so your sleep is far less continuous. Now, some of those awakenings will be of conscious recollection the next day. You'll just remember waking up. Many of them won't be, and so but yet your sleep will be littered with these sort of punctured awakenings throughout the night, and again, when you wake up the next morning, you don't feel restored by your sleep. You know, fragmented sleep or non-continuous sleep in this alcohol-induced way is usually not good quality sleep that you feel great on the next day. The, the third part of alcohol in terms of an equation is that it's quite potent at blocking your REM sleep, your rapid eye movement sleep, and REM sleep is critical for a variety of cognitive functions, um, some aspects of learning and memory. It seems to be critical for aspects of emotional and mental health.

Andrew Huberman 1:12:03 You've described it before as a sort of self-generated therapy that occurs while we sleep

Narrator 1:12:08 ... which-

Matt Walker 1:12:08 Yeah, it's overnight therapy, you know? It's emotional first aid, uh, is, is REM sleep.

Andrew Huberman 1:12:12 Well, certainly people that don't get enough sleep, um, are very easy to derail emotionally.

Matt Walker 1:12:17 Yeah.

Andrew Huberman 1:12:17 Um, not that one would want to do that to people, but we all sort of fall apart emotionally. Our, I, I, I always think about it's almost like our skin sensitivity can be heightened-

Matt Walker 1:12:27 Yes, absolutely.

Andrew Huberman 1:12:27 ... when we are sleep deprived. Um, our emotional sensitivity, um, is such that when we're sleep deprived, uh, such that it takes a, um, much finer grain of sandpaper to create that kind of friction.

Matt Walker 1:12:41 Yeah.

Andrew Huberman 1:12:41 Things bother us.

Matt Walker 1:12:42 It, threshold too much trigger-

Andrew Huberman 1:12:43 Even online comments bother us when we're sleep deprived-

Matt Walker 1:12:47 (laughs) I, I-

Andrew Huberman 1:12:47 ... and never when we're well rested.

Matt Walker 1:12:48 ... I would love to say that I never look at them, uh, except I look at, uh, maybe-

Andrew Huberman 1:12:53 Well, I should, here, here I-

Matt Walker 1:12:53 ... m- m- maybe every one of them, I-

Andrew Huberman 1:12:54 Here I will editorialize because the notion of not looking at comments is, um, is unreasonable for, to ask of any academic because academics, we are all trained to look at our teaching evaluations-

Matt Walker 1:13:07 Yeah.

Andrew Huberman 1:13:07 ... and just like with online comments, to ignore 20% of them. No, I'm kidding.

Matt Walker 1:13:12 (laughs)

Andrew Huberman 1:13:12 Uh, we look at them all, um, in any event, so in terms of translating this to behavior, I'm not, I don't particularly enjoy alcohol. I guess I'm, might be fortunate in that sense, but I also have never really experienced the, the pleasure of, of drinking, uh, alcohol. I sometimes like the taste of, of a drink, but I never like the sensation, so that's, uh, I don't-

Matt Walker 1:13:30 Hmm.

Andrew Huberman 1:13:30 ... have a lot of, of familiarity with this, but many people do, and I understand that. So let's say, um...... somebody, uh, enjoys a glass of wine or two with dinner, and they eat dinner at 7:00 PM. Is that likely to disrupt their sleep at all? Let's just sort of, uh, let's make this a, a series of gradations.

Matt Walker 1:13:49 Yeah. And the answer is, is yes.

Andrew Huberman 1:13:52 Mm-hmm.

Matt Walker 1:13:52 Um, I think one study just looked at a single glass of wine in the evening with dinner, and, uh, I would be untruthful if I didn't just simply say it has, uh, an effect. And we can measure that, uh, in terms of-

Andrew Huberman 1:14:06 Less REM sleep.

Matt Walker 1:14:07 ... less REM sleep.

Andrew Huberman 1:14:08 Mm-hmm.

Matt Walker 1:14:08 And one of the fascinating studies, I can't remember what dose, I think they got them close to a standard, um, illegal blood alcohol level, so maybe they were a little bit tipsy, and yes, you see all of the changes that we just described. Um, they sort of lose consciousness more quickly, they have fragmented sleep, and they have a significant reduction in REM sleep.

Matt Walker 1:14:30 But what was also interesting, because REM sleep, as we spoke about before, is a time when some hormonal systems are essentially recharged and refreshed, growth hormone being one of them, there was well over a 50%, five zero, drop in their growth hormone release during alcohol-laced sleep at night.

Andrew Huberman 1:14:49 Wow. Wow.

Matt Walker 1:14:50 You know?

Andrew Huberman 1:14:50 And growth hormone is so vital for metabolism and repair of tissues-

Matt Walker 1:14:54 Yeah. Yeah.

Andrew Huberman 1:14:54 ... and, um-

Matt Walker 1:14:55 It's not just for kids.

Andrew Huberman 1:14:55 ... keeping the body fat low and-

Matt Walker 1:14:57 This is essential in adults, yeah.

Andrew Huberman 1:14:58 It's essential. It's essential. Um, along those lines, I, I just wanna highlight the fact that this, um, this information that you're sharing, that growth hormone is released, is strongly tethered to the presence of healthy amounts of REM sleep is interesting to me because I always thought that growth hormone was released in the early part of the night.

Matt Walker 1:15:18 Well, it is released, uh, in-

Andrew Huberman 1:15:19 Mm-hmm.

Matt Walker 1:15:20 ... across both of those, but ac- across the different stages. But what we also know is that when you disrupt REM sleep, there are those growth hormone consequences.

Andrew Huberman 1:15:29 I see.

Matt Walker 1:15:29 So it's not an exclusive, uh, system. Just like with testosterone, we can see changes throughout non-REM sleep, but if you ask when are the peak release rates of testosterone, it's right before we go into REM sleep and then during REM sleep.

Andrew Huberman 1:15:44 And of course, re- testosterone being important both for, for males and for females.

Matt Walker 1:15:48 For men and women, yeah.

Andrew Huberman 1:15:48 Right? For libido and tissue repair and wellbeing.

Matt Walker 1:15:51 Yeah.

Andrew Huberman 1:15:51 Nobody, regardless of chromosomal, hormonal, or any other background, wants to have their normal levels of testosterone reduced acutely.

Matt Walker 1:16:00 No.

Andrew Huberman 1:16:00 That's just a bad ... It, it, it equates to a terrible set of psychological and physical symptoms.

Matt Walker 1:16:05 Yeah, and the mortality risk that's associated with low testosterone is non-trivial.

Andrew Huberman 1:16:09 Prostate cancer.

Matt Walker 1:16:10 Right, exactly.

Andrew Huberman 1:16:11 Yeah, yeah.

Matt Walker 1:16:11 You know? So coming

Matt Walker 1:16:14 back to just the point on REM sleep that you mentioned regarding emotional instability, and we see that, that's one of the things, one of the most reliable signatures of just insufficient sleep. Doesn't have to be sleep deprivation. What we've discovered over the past 20 years here at the Sleep Center is that there is no major psychiatric disorder that we can find in which sleep is normal. And so I think that firstly told us there is a very intimate association between your emotional and mental health and your sleep health. But when it also comes to REM sleep, I think what's fascinating is that it's not just about your emotional health. It's not just about your hormonal health. Um, we've also been seeing other aspects of, you know, cognition. But then there was a, a report, I think it could have been about two years ago, f- out of Harvard. Um, I think it was Beth, uh, Clearman's group. Um, they found that, and they replicated it in two different large populations. If you look at the contribution of different s- sleep stages to your lifespan, REM sleep was the strongest predictor of your longevity. And it was a linear relationship. It wasn't sort of one of these U-shaped or J-shaped curves that we often see with total sleep and mortality risk. It really was linear, that the less and less REM sleep that you were getting, the higher and higher your probability of death. And then they did-

Andrew Huberman 1:17:45 Was that death due to, um, natural causes or accidents?

Matt Walker 1:17:47 It was-

Andrew Huberman 1:17:47 'Cause I could imagine if you're not getting enough REM sleep, you're more likely to drive off the freeway, step off a cliff or-

Matt Walker 1:17:52 Yeah, I think it was all-cause mortal-

Andrew Huberman 1:17:53 ... or just make bad decisions about anything in life, relationships and health-

Matt Walker 1:17:56 Yeah, oh-

Andrew Huberman 1:17:56 ... which can also be life-threatening.

Matt Walker 1:17:58 (laughs) Yeah, I've tried to lean into that and claim that I, um, with those bad relationship situations that, "Oh, I just didn't have enough REM sleep last night, my darling."

Andrew Huberman 1:18:05 Blame REM sleep. The REM sleep defense.

Matt Walker 1:18:07 You know? Yeah. And, uh, but, uh, she's far wiser than, than I thought. But, um, so they've did this great machine learning analysis, and I may get these numbers backwards, but I think for every 5% reduction in REM sleep, there was a 13% associated increased risk of mortality.

Andrew Huberman 1:18:28 Wow.

Matt Walker 1:18:29 Uh, and I could have, I'll have to go back and, and check. But to me, the, and in the machine learning algorithm, what they ultimately spat out was that of all of the sleep stages, REM sleep is the most predictive of your longevity, of your lifespan. So we often, I hear people saying, "How can I get more deep sleep?" Uh, or they sometimes say, "How can I get more dream sleep?" And m- my answer is a question. "Why do you want to get more of that?" And they'll say, "Well, isn't that the good stuff?" And I'll say, "Well, actually all stages of, of sleep are-"

Andrew Huberman 1:19:00 It's all the good stuff.

Matt Walker 1:19:02 Yeah.

Andrew Huberman 1:19:02 Well, it's like the exercise question, and it took decades for people to understand that moving around at, uh, for about 150, probably 180 minutes a week at doing endurance type work, zone two cardio type work, is, is correlated with living longer, feeling better, less diabetes, et cetera. There's really no way around it.

Matt Walker 1:19:24 Yeah.

Andrew Huberman 1:19:24 I mean, you can, um, you can ingest Metformin until the cows come home.

Matt Walker 1:19:29 (laughs)

Andrew Huberman 1:19:29 You can take NMN, all of which I think have, have their place in, um, certain contexts. I'm a big fan of the work surrounding all, all those protocols.

Matt Walker 1:19:36 Yeah, likewise.

Andrew Huberman 1:19:37 But without getting proper amounts of movement-... meaning sufficient numbers of, doesn't matter how many 12-minute exercise regimes you follow per week, you need that threshold level. And it sounds like the same is true of REM sleep and to- and total amount of sleep.

Matt Walker 1:19:54 Yeah.

Andrew Huberman 1:19:54 There's just, y- you, um, you pay the piper somehow.

Matt Walker 1:19:58 Yeah, the return on investment, I mean, to, to flip the coin, the return on investment is, is astronomical.

Andrew Huberman 1:20:03 Mm-hmm.

Matt Walker 1:20:04 You know, I think of sleep, it, it is the tide that moves, you know, that raises all of those health boats.

Andrew Huberman 1:20:11 And the most fundamental layer of mental and physical health. Whenever people ask me, uh, even though I'm not a physician, they'll ask me, you know, "What, what should I, what should I take?" Or, "What should I do?"

Matt Walker 1:20:19 Right.

Andrew Huberman 1:20:19 The first question is always, "How's your sleep?"

Matt Walker 1:20:22 Great. I love it.

Andrew Huberman 1:20:22 Meaning, how well do you sleep every night and, and how, how long are you sleeping?