Using Deliberate Cold Exposure for Health and Performance | Huberman Lab

Andrew Huberman 0:00 (mellow 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, we are going to discuss the use of deliberate cold exposure for health and performance. Temperature is a powerful stimulus on our nervous system, and indeed, on every organ and system of our body. And cold, in particular, can be leveraged to improve mental health, physical health, and performance, meaning for endurance exercise, for recovering from various forms of exercise, for actually improving strength and power, and for enhancing mental capacity. In order to properly leverage deliberate cold exposure for sake of mental health, physical health, and performance, you have to understand how cold impacts the brain and body. So today, we are going to discuss that. We're going to talk about some of the neural circuits and pathways, some of the hormones involved. I promise to make it all clear and accessible, regardless of whether or not you have a scientific background or not. We are also going to discuss very specific protocols that you can apply which leverage variables like temperature, how cold, how to deliver the cold. For instance, whether or not you use a cold shower, cold immersion, ice bath, circulating water or still water, whether or not you're going for walks outside in a T-shirt when it's cold, or whether or not you're purposefully using things like cryo, if you have access to that or not. One thing I can promise you is that by the end of today's episode, you will know a lot about the biology of thermal regulation, that is how your brain and body regulates its temperature. You will also have a lot of tools in your arsenal that you can use and leverage toward improving mental health, physical health, reducing inflammation in the body, improving athletic performance, improving mental performance. I promise to spell out all those protocols in detail as I go along and to summarize them again at the end. I'd like to make a point now that I'm going to make several additional times during today's episode, and that is that temperature is a very potent stimulus for the brain and body. That also means that it carries certain hazards if it's not done correctly. Now, everyone shows up to the table, meaning to protocols, with a different background of health status, and there's simply no way that I can know what your health status is. So anytime you are going to take on a new protocol, that means a behavioral protocol or a nutritional protocol or a supplementation protocol, you should absolutely consult a board-certified physician before initiating that protocol. I don't just say this to protect us, I also say this to protect you. If you'd like to see our medical disclaimer, you can go to our show notes. It's described there. In fact, I encourage you to please do that, and in general, when embarking on new protocols, in particular if they involve strong stimuli like changing temperature or placing yourself into unusual temperatures, I would encourage you to progress gradually. I would also encourage you to not look at gradual progression as the kind of weak version of a protocol. In fact, today I'm going to discuss a really beautiful peer-reviewed study that involved having people do deliberate cold exposure, so they were immersing themselves into water up to about their neck, and the water was actually not that cold. It was only about 60 degrees Fahrenheit, which for most people is pretty tolerable. So nowhere near the kinds of extreme temperatures that one could use in other protocols, and the interesting thing is despite that fairly modest cold temperature, by simply extending the duration of time that people were in that water, they experienced enormous increases in neurochemicals that ought to translate to improvements in focus and mood, and indeed, that's what's been observed in subsequent studies. So again, please see our medical disclaimer in our show notes. Please proceed with caution always. Please also understand that the most potent stimulus isn't always the one that you experience as the most intense in the moment. In fact, I would encourage you to find the minimum threshold of stimulus that will allow you to derive the maximum benefit from each protocol, and indeed I will point out what those thresholds ought to be today. I'll give you some simple formulas, uh, gauges or guides that you can use in order to navigate this extremely interesting and potent tool that we call deliberate cold exposure. Before we talk about deliberate cold exposure and its many powerful

Andrew Huberman 4:23 applications, I'd like to highlight a study that I find particularly interesting and that I think you will find particularly interesting and useful. The title of this study is Brief Aerobic Exercise Immediately Enhances Visual Attentional Control And Perceptual Speed: Testing The Mediating Role Of Feelings Of Energy. Now, the reason I like this study is first of all, it's a fairly large size sample group. They looked at 101 students, these were college-aged students, and they had two groups. One group did 15 minutes of jogging at moderate intensity. So when... They did measure percent heart rates, et cetera, but this would be, uh, analogous to zone two cardio, which I've discussed on this podcast before. Zone two cardio is cardiovascular exercise that places you at a level where you can hold a conversation with a little bit of strain, meaning that you can get the words out, but every once in a while you have to catch your breath, whereas if you were to push any harder, by any mechanism, going faster or on a steeper incline, et cetera, that you would have a hard time carrying out a conversation, so zone two cardio... is, uh, a common f-form of describing that level of intensity that they call moderate intensity. So one group did 15 minutes of jogging at moderate intensity, which I'm translating to roughly zone two cardio. The other group did 15 minutes of relaxation/concentration that is somewhat akin to mindfulness meditation. And then they were analyzed for perceptual speed, visual attentional control, something called working memory, which is your ability to keep certain, uh, batches of information online. Uh, just imagine, uh, someone telling you their phone number and you have to remember that sequence of numbers in your- in your head, uh, for some period of time. That's working memory, and it depends very heavily on the so-called prefrontal cortical networks, uh, which are involved in planning and action. And they also looked at people's feelings of energy, and they measured that subjectively, how energetic people felt. Now, the major takeaways from this study that I'd like to emphasize are that the 15 minutes of jogging group experienced elevated levels of energy for some period of time after they ceased the exercise, whereas the group that did mindfulness meditation actually reported feeling more calm and having less overall energy. Now, that's very subjective, and indeed they used subjective measures to, uh, analyze energy, but what gets interesting is when they looked at performance on these various cognitive tasks. And the two tasks that they used were called the Trail Making Tests. They have different versions of this, version A, version B. I don't want to go into too much detail, but version A essentially involves having a page of numbers that are distributed somewhat randomly, so one, two, three, four, five, six, seven, eight, and- and so on, but distributed randomly across the page, and people have to use visual search to circle those numbers in sequence. So this involves visual attention, it involves some motor skills, involves a number of things that certainly require energy and focus. The second test was the Trail Making Test Part B, as I mentioned earlier, and this involved also circling numbers in sequence, but interspersed between those numbers were letters. So rather than just having to circle off numbers in sequence, they actually had to connect one, then the letter A, then two, then the letter B, et cetera. And remember, these are randomly distributed across a page. The major takeaway from the study is that the group that did the 15 minutes of moderate exercise prior to these two tests showed significant decreases in the amount of time required to complete these tests accurately. That is interesting, and indeed surprising, at least to me, because there have been many studies looking at the effects of mindfulness meditation on the ability to focus. The key variable in the study turned out to be energy, this feeling, subjectively measured feeling I should say, of having more energy, and thereby the ability to focus, especially in these high cognitive demand tasks. Now, the takeaway from this study for all of us I think is pretty straightforward. If you are going to sit down to do some work that requires focus and working memory and cognitive attention, and especially if it's, um, visual spatial control, meaning you have to search for things on a page, you have to organize things on a page, so this would be writing, arithmetic, basically cognitive work of any kind, 15 minutes of moderate exercise done prior to that work bout could be very beneficial for you. This does not mean that mindfulness meditation would not be of benefit to you. I wouldn't want you to conclude that. But if you had to choose between doing 15 minutes of mindfulness meditation and doing 15 minutes of moderate exercise prior to a cognitive work bout, I would say the 15 minutes of moderate exercise would be more valuable, at least based on the data in this paper. In many previous podcasts, I've talked about the powerful effects of doing things like mindfulness meditation and other forms of NSDR, non-sleep deep rest, so these could be 20-minute naps or just lying there quietly with your eyes closed, or yoga nidra, or NSDR scripts are available on YouTube and various other places free of cost of any kind. You can just go to YouTube, put in NSDR, non-sleep deep rest. Those protocols have been shown to be very beneficial for enhancing neuroplasticity, the changes in the brain and body that encode or shift the neural circuits that allow for memory to change, that allow for learning to occur after a learning bout. What I'm referring to today and in this particular study is the use of moderate exercise in order to increase one's focus and attention in order to trigger that neuroplasticity. So the simple sequence here is get energetic and alert, do that prior to the learning bout, engage in the cognitive work or learning bout, and then mindfulness meditation, NSDR, and so forth should follow. And if you would like to access this paper and like to look more at the details in the paper, uh, we'll be sure to put a link in the show notes. The first author is LeGrand, and again, the title of this paper is Brief Aerobic Exercise Immediately Enhances Visual Attentional Control and Perceptual Speed, Testing the Mediating Role of Feelings of Energy. And I also just want to emphasize "immediately." I think most (laughs) people out there are interested in tools and protocols that work the first time and that work every time, and indeed, I think this protocol fits that

Andrew Huberman 10:47 bill. I'm pleased to announce that I'm hosting two live events this May. The first live event will be hosted in Seattle, Washington on May 17th. The second live event will be hosted in Portland, Oregon on May 18th. Both are part of a lecture series entitled The Brain Body Contract, during which I will discuss science and science-based tools for mental health, physical health, and performance. And I should point out that while some of the material I'll cover will overlap with information covered here on the Huberman Lab Podcast and on various social media posts, most of the information I will cover is going to be distinct from information covered on the podcast or elsewhere. So once again, it's Seattle on May 17th, Portland on May 18th. You can access tickets by going to hubermanlab.com/tour, and I hope to

Andrew Huberman 11:32 see you there.Before we begin, I'd like to emphasize that this podcast is separate from my teaching and research roles at Stanford. It is however part of my desire and effort to bring zero cost to consumer information about science and science-related tools to the general public. In keeping with that theme, I'd like to thank the sponsors of today's podcast. Our first sponsor is Athletic Greens, also called AG1. I started taking AG1 way back in 2012, so I'm delighted that they're sponsoring the podcast. The reason I started taking AG1 and the reason I still take AG1 once or twice a day is that it covers my foundational vitamin, mineral, and probiotic needs. It also has adaptogens and things like zinc for immune system function, but the probiotics are one of the key features in there. I've done several podcasts on the gut microbiome, which are these trillions of microbiota that live in our digestive tract and that are crucial for our immune system, brain function, and so on. One way to enhance our gut microbiome to ensure that it's healthy is to make sure that we get the correct probiotics, and Athletic Greens has the correct prebiotics and probiotics that ensure a healthy gut microbiome. If you'd like to try Athletic Greens, you can go to athleticgreens.com/huberman to claim a special offer. They'll give you five free travel packs that make it very easy to mix up Athletic Greens while you're on the road, so in the car and on the plane. I should mention that Athletic Greens is delicious. I love the way it tastes. I mix mine with some water and a little bit of lemon or lime juice. This special offer is the five free travel packs plus a year's supply of vitamin D3 K2. Vitamin D3 has been shown to be important for a tremendous number of biological functions. Many of us who get sunlight get enough vitamin D3. Many of us, even if we do get sunlight, do not get enough vitamin D3. So the year's supply of vitamin D3 also has K2, which is important for cardiovascular function, for calcium regulation. Again, go to athleticgreens.com/huberman to get the five free travel packs and the year's supply of vitamin D3 K2. Today's episode is also brought to us by ROKA. ROKA makes eyeglasses and sunglasses that are of the absolute highest quality. The company was founded by two all-American swimmers from Stanford, and everything about their eyeglasses and sunglasses were designed with performance in mind. Now, the glasses were initially designed for athletic performance, meaning they were designed to be worn while cycling or running, and indeed you can wear them while cycling or running. If you get sweaty, they won't slip off your face. They're very lightweight. In fact, you hardly ever remember that they're on your face, at least I can't remember that they're on my face. I wear the sunglasses when I drive, I wear readers at night. But they're not just for athletic performance. They have a terrific aesthetic, so you could wear them to the office or to work or to school. They look great, unlike a lot of high performance sunglasses out there that make people look like cyborgs. These you would be happy to wear anywhere. If you'd like to try ROKA glasses, you can go to roka.com, that's R-O-K-A dot com, and enter the code Huberman to save 20% off your first order. Again, that's ROKA, R-O-K-A dot com, enter the code Huberman at checkout. Today's episode is also brought to us by Helix Sleep. Helix Sleep makes mattresses and pillows that are uniquely designed to your sleep needs. Everybody knows the importance of sleep for mental health, physical health, and performance. But probably what everyone doesn't realize is that you have unique sleep needs. Your body and indeed the way you sleep need to be matched to the correct mattress in order to get the best possible sleep. Helix understands that, and if you go to their website, they have a brief two-minute quiz that anyone can take that will match your body type and sleep preferences to the perfect mattress for you. So they ask questions like do you sleep on your side, your back, or your stomach, or maybe you don't know. Do you tend to run hot or cold through the night, or maybe you don't know. I matched to the Dusk mattress, D-U-S-K, because I wanted a mattress that wasn't too firm nor too soft, and I've been sleeping on that mattress for over a year now. It's the best sleep I've ever had. So if you're interested in upgrading your mattress, go to helixsleep.com/huberman, take their two-minute sleep quiz, and they'll match you to a customized mattress. And you'll get up to $200 off any mattress order and two free pillows. They have a 10-year warranty, and you get to try the mattress out for 100 nights risk-free. They'll even pick it up for you if you don't like it, although I think you will like it. I certainly love mine. Again, if you're interested, go to helixsleep.com/huberman to get up to $200 off your mattress order and two free pillows.

Andrew Huberman 15:37 Okay, let's talk about the use of cold for health and performance. I confess I love this topic, because it takes me back to my undergraduate years when I worked in a laboratory studying cold physiology, its effects on the brain, and its effects on the body. And over the years, I've always kept track of the literature in this area, and indeed there have been some tremendous discoveries both in animal models, so in rodents like mice and rats, but also in humans, and today we're going to talk about both categories of studies, and I will be careful to point out when discoveries were made in animal models and when they were made in humans. A key point when thinking about the use of cold as a tool, and the key point is that you have a baseline level of temperature that is varying, changing across the 24-hour cycle. So any use of deliberate cold exposure is going to be superimposed on that rhythm, that circadian rhythm, meaning that 24-hour rhythm. The basic contour of your circadian rhythm in temperature is that approximately two hours before the time you wake up is your so-called temperature minimum. So your temperature minimum is a time within the 24-hour cycle when your body temperature is at its lowest. Okay? So if you normally wake up around 6:00 AM, your temperature minimum is probably about 4:00 AM. If you normally wake up at about 7:00 AM, your temperature minimum is probably about 5:00 AM. It's not exactly two hours before your wakeup time; it's approximately two hours before your wakeup time. Now, as you go from your temperature minimum to the time in which you're going to awake, your temperature is rising slightly, and then at the point where you wake up, your temperature starts to go up more sharply and will continue to go up into the early and sometimes even into the late afternoon.And then sometime in the late afternoon and evening, your temperature will start to decline. And indeed, as you approach sleep, your body temperature will drop by anywhere from one to three degrees and in fact, that decrease in core body temperature is important, if not essential for getting into and staying in deep sleep. Okay? So temperature rises with waking, that's easy to remember, it tends to continue to rise throughout the day, and in the late afternoon and evening, your temperature will start to go down and the drop in temperature actually helps you access sleep. That background or what we call baseline circadian rhythm in core body temperature is important to remember because it helps us frame both the effects of deliberate cold exposure and it helps us frame when you might want to use deliberate cold exposure in order to access specific states. It also points to times within the 24-hour cycle when you might want to avoid using deliberate cold exposure if your primary goal

Andrew Huberman 18:41 is to get to sleep. Okay, so that's the circadian rhythm and temperature. Now I just briefly want to touch on thermal regulation at the level of the body and the brain, and this will be very surprising to many of you. Let's do what's called a Gedankenexperiment, which is a thought experiment. Let's say I send you out into the desert heat for a jog or a run and it's very hot outside, you know, a 102 degrees or a 103 degrees, and you start to move, you start to sweat, and of course your core body temperature goes up. Now, then I offer you a cold towel, maybe a really, really cold towel, and this towel is saturated with water so you could actually squeeze the water out of that and cool your body off, and our Gedankenexperiment is for me to say, "Okay, where are you going to place the towel? How are you going to cool yourself off?" And I'm guessing that most of you would think that the best way to cool yourself off would be to drape that towel over your head, maybe your neck, over your torso, that it would feel really, really good and it would cool you off. Well, that's exactly the wrong approach if you want to cool off, and in fact, if you were to use that approach, your body temperature would continue to increase even more. Yes, even more than had you not placed that cold towel on your head or your torso. And here is why. Thermal regulation, meaning your brain and body's ability to regulate your internal core temperature, is somewhat like a thermostat, and that thermostat resides in your brain. So if you think about the thermostat in your home or apartment, if it's too warm in your home or apartment and you were to take a bag of ice and to put it on that thermostat, what would the thermostat do? It would register the environment as artificially cool, right? It would think that the environment was actually much colder than it is. And so as a consequence, it would trigger a mechanism to further increase the temperature in the room. And you have such a thermostat as well. It's called the medial preoptic area of the hypothalamus. The hypothalamus is a small region of brain tissue about over the roof of your mouth and a little bit in front of that. So it's, uh, basically right behind your nose and over the roof of your mouth, and it's a collection of neurons. Those neurons have a lot of different functions that include things like, uh, the control of aggression, the control of sex behavior, the control of temperature regulation, and so on. The medial preoptic area has connections with the rest of the brain, or areas within the brain I should say, and with many areas within the body. It receives input from receptors in our skin and inside our body that register temperature, and it acts as a thermostat. So if the surface of your body is made cool, your medial preoptic area will send signals by way of hormones and by way of chemicals that will serve to heat your body up. So what this means is that if you want to cool down, the last thing you want to do is to bring a cold surface of any kind, towel or splashing water, to the majority of your body surface. That might be very, very surprising to you, uh, and you might say, "Wait, if I want to cool down, I should jump into a cold lake," or something of that sort. That's a different thing altogether. What I'll tell you, and we'll get into this in more depth later, is that if you really want to cool down quickly and efficiently, you should leverage particular portals, meaning particular sites on your body where heat can leave your body more readily and where cooling can have a dramatic and fast impact on your core body temperature. It can even save your life if you're going hyperthermic. We're going to talk more about the specific protocols to reduce core body temperature for sake of performance and avoiding hyperthermia later in the episode. Hyperthermia, of course, is a very, very dangerous situation because while your body can drop in core temperature somewhat and still be safe, you can't really increase your body temperature that much before your brain starts to cook and other organs start to cook, and by cook I mean the cells actually start to die. So you have to be very, very careful with the use of heat. Heatstroke is no joke. People die from heatstroke all the time. You really want to avoid that. One way to avoid that is to cool the appropriate surfaces of your body, and the appropriate surfaces in this case are the upper cheeks or the, I would say the upper half of the face, the palms of your hands, and the bottoms of your feet. I've talked about this on the podcast before and in the guest episode with Dr. Craig Heller, my colleague in the biology department at Stanford, but just very briefly, these surfaces, the upper half of the face, the palms of the hands, and the bottoms of the feet are what we call glabrous skin surfaces. G-L-A-B-R-O-U-S, glabrous. And those surfaces are unique in that just below them, the vasculature is different than elsewhere in the body. Normally, the passage of blood goes from arteries to capillaries to veins, but...Just beneath the glabrous skin on the bottoms of feet, the hands, and the upper half of the face, you have what are called arteriovenous anastomoses. These are portals of blood that go directly from arteries to veins, and in doing so, allow the body to dump heat more readily, more quickly. So as it turns out, that if you are to cool the palms of the hands, the bottoms of the feet, and the upper half of the face, you can more efficiently reduce core body temperature for sake of offsetting hyperthermia and for improving athletic performance and maybe even cognitive performance. So, we will return to the specific protocols for doing that later in the episode. I'll give you a lot of details about how to do that, how to do that without the use of any fancy or expensive technology. There are some technologies that are now commercially available, for instance, the so-called CoolMitt that will allow you to do that with maximum efficiency, but I'll also give you some at-home methods, uh, to do this, uh, either in the gym or on runs or for sake of cognitive work. Okay. So, the two key themes, again, are understand that baseline circadian rhythm and temperature, and understand that the best way to cool the body is going to be by making sure that something cold contacts the bottoms of your feet, the palms of your hands, and the upper half of the face. Ideally, all three of your goal is to lower core body temperature quickly. And again, just cooling off the back of your neck or the top of your head, or your torso with a towel is going to be the least efficient way to lower core body temperature, and might even increase body temperature under

Andrew Huberman 25:26 certain conditions. Okay, with those two points in mind, we can start to think about directed deliberate cold exposure protocols, and there are a number of different reasons to use deliberate cold exposure, and I want to separate those out for you. There are cold protocols that have been tested in peer-reviewed studies that are designed to improve mental performance. They are designed to improve things like resilience, or your grittiness, or your ability to move through challenge, or to regulate your mind and your internal state under conditions of stress. And we can define stress very specifically as times when adrenaline, also called epinephrine, and/or norepinephrine, also called noradrenaline, are elevated in your body. Forgive me for the noradrenaline-norepinephrine, adrenaline-epinephrine nomenclature, I didn't make that up. Turns out that every once in a while, scientists disagree. Imagine that. And you'll get multiple scientists naming the same molecule different things, okay? So epinephrine and adrenaline are the same thing, I will use them interchangeably. Norepinephrine and noradrenaline are the same thing, I will use those terms interchangeably. Noradrenaline and adrenaline are often co-released in the brain and body, so they work as kind of a pair to increase our level of agitation, our level of focus, and our desire and our ability to move. They are often co-released from different sites in the brain and body with dopamine, a molecule that is commonly misunderstood as the molecule of pleasure, but is actually the molecule of motivation, reward, and pursuit. So dopamine, norepinephrine, and noradrenaline tend to be released together under certain conditions, and today, you will learn how deliberate cold exposure can be used to cause increases in the release of several, if not all of these, in ways that can improve your levels of attention and your mood. But the key point is that your mental state is shifted when you are exposed to certain forms of cold, and many people use deliberate cold exposure specifically to shift their body state as a way to train their mental state so that they can better cope with stress in real life. And by real life, I mean, when life presents stressful events. And I will give you specific protocols as to how you can do that. In other words, how you can become more resilient through the use of deliberate cold exposure. Now, because of the ways in which deliberate cold exposure can increase this category of chemicals called the catecholamines that includes dopamine, norepinephrine, and epinephrine, it can also be used to elevate mood for long periods of time. And I'm going to discuss a specific protocol that has been shown to increase these chemicals anywhere from 2.5X, so 250%, to as high as 500%, five times over baseline. Now, you might be asking whether or not it's a good thing to raise chemicals like norepinephrine and dopamine to such a great degree, whether or not that's healthy for us, whether or not they can harm us, but it turns out that these elevations in norepinephrine and dopamine are very long-lasting in ways that people report feeling vast improvements in mood and vast improvements in levels of cognitive attention and energy. So, by my read of the literature, these seem to be healthy increases in our baseline levels of these chemicals in ways that can really support us. So, I'll give you a protocol for that. Now, those are some of the mental effects of deliberate

Andrew Huberman 29:02 cold exposure, but deliberate cold exposure has also been studied in animal models and in humans in the context of increasing metabolism, even in converting certain fat cells that we call white fat cells, which are the ones where energy is stored, they're the ones that we typically think of as kind of blubbery fat, to beige or brown fat, which is thermogenic fat, meaning that it can increase core body temperature and serves as kind of a furnace by which we increase our core metabolism. So, with a very broad stroke, I can say that white fat is generally the kind of fat that people want less of, and beige fat and brown fat is generally the kind of fat that if you're going to have fat cells, and you certainly need fat cells, that you want more of. They are thermogenic. They help you stay lean. They actually serve as a reservoir for heating your body up if you're ever confronted with a cold challenge. So, we're going to talk about how to use cold for metabolism as well. And of course, people are using deliberate cold exposure to reduce inflammation post-exercise, to reduce inflammation generally.And people are also using cold to enhance performance in the context of strength training, in the context of endurance training, and we will talk about

Andrew Huberman 30:11 those data as well. But where I'd like to start is with mental performance, and I'd like to detail what happens when we deliberately expose ourselves to cold. It's key to point out the word deliberate. If I don't say otherwise, then throughout this episode, if I say cold exposure, I mean deliberate cold exposure. And the reason I point that out is that as my colleague, David Spiegel in the Department of Psychiatry at Stanford says, "It's not just about the state that we are in, it's about the state that we are in and whether or not we had anything to do with placing ourselves into that state, and whether or not we did that on purpose or not." And what he really means by that statement is that there are important effects of what we call mindset. Mindset was a topic discussed in the guest episode with Alia Crum some weeks ago. If you haven't seen that episode, I highly recommend it, and the science of mindset tells us that if we are doing something deliberately and we believe that it's going to be good for us, it actually can lead to a different set of physiological effects than if something is happening to us against our will or without our control. Now, this is different than placebo effects. Placebo effects are distinct from mindset effects. If you want to learn more about that distinction, please see the episode with Alia Crum. But again, when I talk about cold exposure in this episode, I'm talking about deliberate cold exposure, meaning that you are placing yourself into a cold environment on purpose in order to extract a particular set of benefits. When we talk about deliberate cold exposure, almost always that means getting uncomfortable, and one of the most common questions I get when discussing the use of cold for sake of mental or physical performance, metabolism, et cetera, is how cold should it be? How cold should the water be? How cold should the environment be? And I just will tell you now and I'm going to say this again and again throughout the episode, because it will continue to be true throughout the episode and long after the episode is over, how cold depends on your cold tolerance, your core metabolism, and a number of other features that there is simply no way I could know or have access to. So, I would like you to use this rule of thumb: if you are using deliberate cold exposure, the environment that you place yourself into should place your mind into a state of, "Whoa, I would really like to get out of this environment, but I can stay in safely." Okay? Now, that might seem a little bit arbitrary, but let's say you were to get into a warm shower and it would feel really, really nice, and you were to start turning down the warm and turning up the cold. There would be some threshold at which it would feel uncomfortable to you, and if you were to continue to make a little bit colder than that, you would really want to get out of the shower, but you were confident that you could stay in without risking your health, right? Without risking a heart attack. Now, that's very different than jumping into a very, very cold lake, or, you know, I've seen these images of people that will cut holes into, um, you know, frozen over lakes and they'll get into that cold water. If you are trained to do that and you have the right conditions, et cetera, that can be done reasonably safely, but that's certainly not what I would start with, and for many people, that would be too cold, and indeed, some people can go into cold shock and can die as a consequence of getting into that extremely cold water very quickly. Now, that's not to scare you away from deliberate cold exposure. It's just to say that there's no simple prescriptive of how cold to make the environment in order to extract maximum benefit for mental or physical performance. So, the simple rule of thumb is going to be place yourself into an environment that is uncomfortably cold, but that you can stay in safely, okay? And you'll have to experiment a bit, and that number, meaning that temperature, will vary from day to day. It will vary across the 24-hour cycle because of that endogenous, meaning that internal rhythm, in temperature that I talked about earlier, low early in the day, rises into the afternoon, drops at night. You can actually do this experiment if you like. Try getting into a cold shower at 11 o'clock at night, if you want, versus try doing it in the middle of the afternoon. It's quite a different experience, and by quite a different experience, I mean it's qu- it requires quite a different degree of resilience and leaning into the practice. Your willpower will have to be higher, I suspect, late in the day as it compared to early in the day. But that will vary, of course, between individuals as well. So, the most common question I get about deliberate cold exposure is how cold should the water be, and we've answered that with uncomfortably cold to the point where you want to get out, but you can safely stay in.

Andrew Huberman 34:53 The second most common question I get about deliberate cold exposure is whether or not cold showers are as good, better, or worse than cold water immersion up to the neck, for instance. I also get a lot of questions about whether or not cryo chambers are better than all the others, et cetera, et cetera. I'm going to make all of that very simple for you by saying cold water immersion up to the neck with your feet and hands submerged also is going to be the most effective. Second best would be cold shower. Third best would be to go outside with a minimum amount of clothing, but of course, clothing that is culturally appropriate and that would allow you to experience cold to the point where you would almost want to shiver or start shivering. Now, there are a number of different important constraints that are going to dictate whether or not you use one form of cold exposure or the other. For instance, some people don't have access to cold water immersion. They don't have access to ice baths or cold water tanks, uh, cold ocean or cold lakes, et cetera. In that case, showers would be the next best solution. I do want to emphasize that there have been very few, if any, studies of cold showers, and you can imagine why this would be the case. In a laboratory, you want to control for as many var- variables as possible. So-Placing people into a cold water immersion or an ice bath up to the neck and insisting that they keep their hands and feet under is very easy to control. It means that everyone can do essentially the same thing. Whereas with cold showers, people are different sized bodies, some people are going to put their head under, some people are going to, are going to lean forward. Measuring the amount of cold wa- water exposure on the body is very hard to do, and so there aren't a lot of studies of cold showers, but of course, a lot of people don't have access to cold water immersion, so they have to use cold showers. And if you don't have access to both, of course, then going outside on a cold day can be of benefit. But I will point out that the heat transfer from your body into water is much higher, four times greater, if not even greater depending on the temperature of the water, in water as opposed to in air. So it's going to be much more efficient to do cold water immersion than anything else, cold showers after that, and put yourself into a cold environment would be the third best thing. I'm not going to get into cryo chambers because they carry quite a high degree of cost and again, there aren't many studies of them. So if you have access to cryo chambers, I'm sure that the cryo chamber facility has told you about all these incredible benefits and I don't doubt that some of those benefits truly exist, but most people just don't have the resources or the access to those. So we're going to leave cryo chambers out of today's discussion. And of course, I realize there's a fourth category of cold exposure out there, people who are wearing ice vests, believe it or not those exist, ice underwear, yes, those exist. You can look for them on Amazon if you like. They are putting cold packs in their armpits or in their groin or elsewhere in order to stimulate some of the effects of cold on mental and physical performance. I'm not going to address those in too much detail today. They can be efficient in certain ways, but as you will learn about later in the episode, cooling the palms, the upper face, and the bottoms of the feet, is going to be far more efficient and unfortunately, I think most of the people that are using ice packs to increase their core metabolism are not aware of the glabrous skin cooling and how it can be a very, very potent stimulus. So we'll return to that, uh, later. Unless I say otherwise, I'm mainly going to be focusing on cold water immersion

Andrew Huberman 38:27 and cold showers. So let's talk about protocols for enhancing mental health and performance using deliberate cold exposure. What happens when we get into cold is that we experience an increase in norepinephrine, in noradrenaline release, and in adrenaline release. The fact that cold exposure, deliberate or no, increases norepinephrine and epinephrine in our brain and body, means that it is a very reliable stimulus for increasing norepinephrine and epinephrine. And that's sort of an obvious statement, but that obvious statement can be leveraged to systematically build up what we call resilience. Now, when we experience a stressor in life, whether or not it's something bad happens in our relationship or something bad happens in the world and we feel stress, that stress is the consequence of increases in norepinephrine and epinephrine in our brain and body. Very similar, if not identical to the kinds of increases that come from deliberate cold exposure. So deliberate cold exposure is an opportunity to deliberately stress our body and yet because it's deliberate, and because we can take certain steps which I'll describe in a moment, we can learn to maintain mental clarity, we can learn to maintain calm while our body is in a state of stress. And that can be immensely useful when encountering stressors in other parts of life. And that's what we call resilience or grit, our ability to ... Or mental toughness, our ability to lean into challenge or to tolerate challenge while keeping our heads straight, so to speak. So one simple protocol for increasing resilience is to pick a temperature that's uncomfortable, of shower or cold immersion, and then to get in for a certain duration of time, and then to get out. Now it's important to understand that people experience different levels of norepinephrine and adrenaline release when getting into cold water. Some people, because they dread the cold so much, will actually experience norepinephrine and epinephrine increases even before they get into the cold water or under the cold shower. Now you may have experienced this. I've certainly experienced this. I'm dreading it, I don't want to do it, and I have to force myself to do it. And indeed, epinephrine and norepinephrine and its surges can be thought of as sort of walls that we have to confront and go over. And I'd like you to conceptualize them that way because it allows us to build protocols that can be very objective and can allow us to monitor our progress in terms of building resilience. So one option is to simply say, "Okay, I'm going to force myself to get into the cold shower for one minute." How cold? Again, uncomfortably cold, but you can stay in safely. Or "I'm going to get into the ice bath for one minute." Ice baths are very cold (laughs) , uh, inevitably, and what is also inevitable is that when you get into the cold, you will experience a surge in epinephrine and norepinephrine. That's non-negotiable because it's mediated by cold receptors on the surface of your body and your skin, and the way that they trigger the release of norepinephrine and epinephrine, not just from the adrenals, from the adrenal glands above your kidneys, but also from regions of your brain like the locus coeruleus which cause increases in attention and alertness, and from other locations in your body where epinephrine and norepinephrine are released. In other words, cold is a non-negotiable stimulus for increasing epinephrine and norepinephrine. Even if you are the toughest person in the world and you love the cold, that increase in epinephrine and norepinephrine is going to happen. So the way to think about norepinephrine and epinephrine in this context of building mental resilience is that you have two options. You can either try to extend the duration of time that you are in the deliberate cold exposure, so going from one minute to 75 seconds to two minutes and so on over a period of days, orOne way to approach this, and the way that I particularly favor, is to take the context of the day and the moment into account. Meaning, we have different levels of grit and resilience on different days, and depending on the landscape of our life at the time, even the time of day that we're doing these protocols, and start to be able to sense the release of epinephrine- epinephrine, excuse me, and norepinephrine in our brain and body, and see those as walls that we want to climb over in order to build resilience, and to start counting the number of walls that we traverse and the distance between those walls as we do deliberate cold exposure. Let me give you an example of the timed protocol, because that one is very straightforward, although I do not think it is as pr- powerful for building mental resilience. The timed protocol would be Monday, I do one minute of deliberate cold exposure at a given temperature, Wednesday, I extend that by 50%, and Friday, I do deliberate cold exposure for twice as long as I did on Monday. And if I were to continue that every week, Monday, Wednesday, Friday, I would continue to either increase the duration or I would lower the temperature and reduce the duration, this kind of thing, very much like sets and reps in the gym. Now, that option is very objective, right? You could even log it in a book. And as you develop the ability to stay in cold temperatures, even progressively colder and colder temperatures for longer and longer periods of time, you will become more resilient. What do I mean by that? Well, my operational definition of resilience is that you are able to resist escape from the stressor, the cold, by virtue of your willpower, which is really your prefrontal cortex causing top-down control on your reflexes and your limbic system and your hypothalamus, which are basically telling you to get out of that cold water, get out of that cold environment. And in doing so, you are basically getting better at controlling your behavior when your brain and body are flooded with norepinephrine and epinephrine. That's a very reductionist way to explain resilience or grit or mental toughness, but it's a reductionist way of explaining it that is very closely tied to the biology and to the psychology, and it is a fact that norepinephrine and epinephrine release in the brain and body are the generic universal code for stressor. There is no unique chemical signature for different forms of stressors. That is the only one. Although, of course, there are other chemicals involved as well. So, you could go for time and you could try and reduce the temperature and increase the time over a period of days or weeks. Now, that's an attractive way to approach things, but the problem is that you don't have an infinite amount of room with which to lower temperature, because eventually you will get into temperatures that are either so cold that they are dangerous or you have to stay in cold temperatures for such long periods that it becomes impractical, because presumably you also have to take care of other aspects of your life. You can't just sit all day in the ice bath. Now, for that reason, I favor a protocol in which you build mental resilience and mental toughness through two different types of protocols. The first one involves counting walls. Now, what do I mean by walls? I mean the sensation of, "No, I don't want to do this," and the idea or the sensation in your brain and body that you actually want to leave that environment and go warm up. Now, again, for some people, that will be even before getting into the ice bath or cold shower. So, if you are feeling very resistant to getting into the ice bath or cold shower and you manage to do that, that's going over what I would call one wall. Okay? Then, for some period of time, you might actually feel comfortable in the ice bath, cold water, or cold shower, and you feel like you could stay there for some period of time, that you could stay there for a minute or two minutes. But inevitably, the next wall will arrive, and I would encourage you to pay attention to when that next wall arrives and actually having an awareness, that so-called interoceptive awareness, as we call it, of when that next surge in adrenaline/epinephrine comes, or whether or not it reaches a certain threshold in your brain and body that you feel you want to get out, and you're able to stay in for even just 10 seconds longer. That means you've traversed yet another wall. And if you continue to stay in that cold environment, you will find that the next wall will come and the next wall will come. Now, eventually, of course, you will get very, very numb depending on how cold it is, and you could also place yourself into danger. So, you have to maintain cognitive control, counting these walls, traversing these walls, but getting out at some point, of course. So, my favorite protocol for building mental toughness, A.K.A. grit, A.K.A. resilience, is to take into account that some days, just getting into the ice bath or cold shower represents a wall, some days it doesn't. Some days you get in and you feel like you could go 10 minutes. Other days, you get in and you feel like you could only go a minute. And setting a designated number of walls before you start the protocol is going to be very beneficial here. So, you say, "As long as I can do it safely, I'm going to do three walls today. The first wall is getting in, the second wall will arrive when it arrives, and the third wall will arrives when it arrives, and I'll get over that wall and then I'll get out." The next day, you might do five walls. The next day, you might do three walls again, but you might lower the temperature. This gives you tremendous flexibility, and indeed, it gives you much more latitude to be able to use the same temperatures in different ways, or to reduce the temperature only a little bit and still get a lot of stimulus, meaning a lot of results out of a given protocol. Whereas people who are just going for temperature and time eventually become cold-adapted. They get very, very good at doing three minutes or six minutes or even T- ten minutes at a given temperature, and so then they feel like they have to lower the temperature even more and even more, and eventually, they just bottom out. There's nowhere else to go, there's nowhere to get...... improvements out of the protocol, at least not in terms of mental resilience. Of course, there's still the positive effects on inflammation and metabolism, etc., that we'll talk about e- in a little bit. But the key thing here is to design protocols that are going to work for you over time. And for you very, very hardy, very, very tough guys and gals out there that can get right into an ice bath or a very, very cold immersion, and you can just grind it out for 6 or 10 minutes, or you can even do that by remaining peaceful, well, more points to you, but guess what? That's the equivalent of already having loaded up the barbell with 600 pounds and done your 10 reps. There's not a whole lot more variable space with which to get benefits from that stimulus. And in the weight room, people understand that you can adjust, for instance, the speed of the movement, or you can start combining that movement with pre-exhaustion, etc. With cold exposure, you don't have as much variable space to play with. So if your goal is to build resilience, either go for time as a function of temperature, or what I suggest is to start recognizing these walls as an experience of resistance in you and going over those walls. Set a certain number of walls that you're going to go over on a given day and do that at a given temperature, and then to mix it up. And ideally, you might even throw in one more wall at the end if you're really feeling bold and brave because that's going to build out further resilience. But if you want cold exposure to work for you for sake of building up resilience and mental toughness over time, you're going to want to vary this parameter space in some sort of way. And you don't have to be super systematic about it. That's the beauty of this kind of approach, because you're relying on the fact that those walls really represent times in which you are forcing your top-down control, your prefrontal cortex, to clamp down on your reflex, and you're learning behavioral control in the context of your body having elevated levels of these catecholamines, norepinephrine and epinephrine. And that translates to real life in a much more realistic way, I believe, because in real life, you're not really engaging in stressors for a given amount of time, that you know how long it's going to last, and you know the context. No. Most stressors arrive in the form of surprises we don't like, text messages that deliver bad news, information about the outside world or real world and online interactions that send our system into a state of increased norepinephrine and epinephrine. And if you start to think of those as walls that you can tolerate and climb over while staying calm and clear of mind, then y- you can really imagine how the ice bath and other forms of cold exposure are really serving to train you up for real life stressors.

Andrew Huberman 50:57 Okay, the next question that I always get is, "What should my mental state be while I'm exposing myself to this uncomfortable yet safe condition of cold?" Well, you have two options, and there are probably other options as well. One is to try and calm yourself, to remain as mentally still as possible. The other is to lean into that challenge, and so to grind it out. And here, I have to say that this is a lot like teaching someone to drive on a gravel road. For any of you that have driven on a gravel road, you know that there is no optimal speed for all gravel roads. It depends on the density of the gravel, etc., and the vehicle, etc. So for instance, on some gravel roads when you start to drive and the dust starts to kick up, your best option is to drive fast and put that dust cloud behind you. On other gravel roads, if you try and do that, the dust actually kicks up around the vehicle and it makes it hard to see, and sometimes you have to slow down. The same thing is true for getting through deliberate cold exposure. Sometimes it's easier to calm yourself. One way to do that is through double inhales through the nose and extended exhales through the mouth, or simply by trying to control your breathing and reduce the pace of your breathing, and increase the volume of your breathing. I have to say that everyone experiences a shortening of breath when they get into uncomfortably cold water. That is a universal physiological response. Everyone also experiences a 30% to 80% decrease in cognitive function, in particular of their frontal cortex. The metabolism of your frontal cortex goes down. The metabolism, meaning the activity of brain areas associated with stress and panic, goes way up. And so anchoring your mind in cognitive activities as you get into the cold can be very, very helpful for maintaining clarity of mind. In fact, one thing that I sometimes recommend is that people try and engage in some sort of cognitive exercise while in the cold, not as a form of distraction, but as a way to maintain clarity of thinking and to learn how to do that when the body is flooded with all these chemicals that make us stressed. So for instance, you could do math problems, and not two plus two equals four, not, you know, three times three equals nine, but things that require a little bit more focus and attention, working memory, and so forth. You could also start to have thoughts that you deliberately impose a full sentence structure on. That's actually quite tough. You could try and recall specific bouts of information that are challenging. This is teaching your mind how to stay online, or rather I should say this is you teaching your prefrontal cortex how to stay engaged while you have high levels of stress in your body. Years ago, I had a friend who works in the neuroscience world, research neuroscientist, who was obsessed with, um, this very bizarre sport that I don't necessarily recommend at all, which is the combination of boxing and chess. You may have seen this on YouTube, where people will box a round, legitimate boxing around, they're sparring all out often, and then at the end of the round instead of resting in the corner, they actually sit down and play chess, and then they go back to boxing and back to chess. Again, not a sport that I recommend, but the reason he was obsessed with this is because he studies the impact of stress on cognitive performance, and what that particular very bizarre sport was doing was toggling back and forth between different states of mind. Now it's used both to increase-Cognitive clarity for the fighter when they box, because staying calm and clear thinking is very important to winning boxing matches. B- believe it or not, it's not an all-out rage, it's a very calculated game of mental chess and physical chess that's quite high stakes, as you can imagine. It's also used in some circles as a way to teach people how to engage in cognitive performance when their body is simply filled with stress. So in the boxing chess example, (laughs) the replacement for the cold water is actually the boxing, right? It's the thing that's supposed to induce the stress, 'cause getting hit is stressful and the risk of getting hit is stressful for most people. So again, if you think about deliberate cold exposure as a way of just systematically and reliably inducing epinephrine and norepinephrine release and delivering stress, well then this idea of maintaining cognitive clarity and actually engaging in cognitive tasks while in the ice bath or cold shower can actually be very beneficial. Even though it might sound a little bit silly, you are really training up your ability to keep your brain working when the reflex is to shut down the parts of your brain that are involved in deliberate planning and thinking.

Andrew Huberman 55:26 Now, another important aspect of deliberate cold exposure that I rarely, if ever, hear discussed but is vitally important is whether or not you move around or not. Here's the reason. When you get into cold water and you remain there for some period of time, your body is generating heat, and that heat generates what's called a thermal layer that surrounds your entire body. So if you stay still, you are actually warmer than if you move around. You can try this the next time you're doing your deliberate cold exposure. If you're submerged up to the neck, sit there for about 10, 30 seconds and be very, very still of body. In fact, this is the way that most people start to do deliberate cold exposure. They give this very stoic look, they don't blink, they look very peaceful, some of them even look tough, like they're... Or they make a very, um, you know, even, aemotional face and so it looks like they're, oh, they're really tough. But they are so still that, believe it or not, they are not providing the most potent stimulus. If they or you were to move around in that water, what would happen is you'd break up the thermal layer and that you actually experience that as much colder. So if you really want to push the resilience aspect, or for instance if you want to use a given temperature that you're comfortable in, but that you want to increase the stimulus and you want to get some more benefit from mental resilience training, well then get into the cold water, move your body around continuously, but try and keep your mind still or even do some sort of cognitive task. So as you're starting to realize, there are a bunch of different variables that you can play with while maintaining the same temperature of water, and in doing so, really keep you in the zone of what should and absolutely has to be safe for you without having to just continually drop the temperature from say 60 degrees to 55 to 40 to 33, because as I mentioned before, eventually you're going to bottom out. So if you're one of those people that likes to look tough or really relaxed while you're in the ice bath or cold water immersion, just realize that you're actually cheating yourself out of part of the stimulus. Keep those limbs moving, and of course limbs under the water, feet and hands, is going to be a more potent stimulus than hands and feet out, for reasons that should be obvious based on what we talked about in terms of glabrous skin cooling. So keep those submerged, move your body, pedal, maybe move your knees up and down, pedal your feet, and trust me, it's going to feel a lot colder than were you to have remained

Andrew Huberman 57:51 stone still. Another very common question is how often to do deliberate cold exposure. It's tough to make a recommendation on that based on any peer-reviewed study, although there are a few in humans that point to a threshold of 11 minutes total per week. So that's total throughout the week, divided into two or four sessions of two or three minutes or so. Now, that 11-minute cutoff is not a strict threshold, and is actually geared more towards increases in metabolism. We'll get into this a little bit later in the episode. But I think the 11-minute threshold, meaning 11 minutes total of deliberate cold exposure per week, is a pretty good number to use if you need a number in order to keep you consistent. But as we talked about earlier, some of you are going to be in the ice bath or cold immersion or cold shower for one minute, others of you will be in there for 10 minutes, depending on how frequent and how high, if you will, those walls of adrenaline are coming. So for some of you, getting into a cold shower for three minutes total for the whole week will represent a tremendous achievement in terms of willpower and overcoming the resistance to doing that, overcoming those walls. For others of you, three minutes is nothing. So what do I recommend? I recommend that you get at least 11 minutes total per week, but at the point where 11 minutes total per week is very easy for you or is no longer representing a significant mental challenge, meaning you're not experiencing many of these walls, you're excited to get into the cold shower or immersion, you're going through it easily, you're cruising basically, then I would say either lower the temperature, safely of course, extend the duration, safely of course, or increase the frequency so that you're doing this perhaps every day, or maybe five days a week or three days a week. I personally get tremendous benefit from doing deliberate cold exposure three times a week and using the walls method that I described earlier as my gauge for how long to stay in. And typically that means that I'm staying in for anywhere from two minutes to six minutes per session, and that averages out to about 11 to 15 minutes total per week. So again, I do not think that you need to be super strict about these guidelines. It's most important when embracing a protocol, A, that you do it safely, but secondarily that you do it consistently. So find what you can do consistently and then vary the parameters that will allow you to continue to do deliberate cold exposure consistently regardless of whether or not you have access to a shower or cold immersion, et cetera.Okay,

Andrew Huberman 1:00:22 so we've been talking about mental effects and the use of deliberate cold exposure for sake of building resilience, which I do believe can be tremendously powerful. Look, it's no coincidence that the screening and the training for Navy SEALS involves a lot of exposure to cold water. One could argue that it is deliberate because they elect to go to BUD/S, but when they get into the cold water at BUD/S is dictated by the instructors. And the reason they use cold water exposure as the stressor is that it does offer considerable leeway in terms of duration and temperature, in terms of how you can use it as a stressor, whereas things like heat don't offer much variable space, as we say. There isn't a lot of room beyond which you start injuring or even killing people by using heat. So there are a lot of forms of stressors out there, but cold is one that we can titrate, that we can adjust in ways that can allow us to continually build up and/or maintain mental toughness. Now, deliberate cold exposure also has many effects on chemicals other than norepinephrine and epinephrine, most notably the neuromodulator dopamine, which is involved in elevating our mood, making us feel energized, and enhancing our ability to focus, and that has a lot to do with how dopamine engages us in motivated states, tends to narrow our thinking and our behavior into a particular trench of goal-directed behavior. If you want to learn more about dopamine, you can learn a lot about dopamine in our episode about dopamine. It's at hubermanlab.com. You can find it. It's like two and a half hour plus, um, kind of deep dive into all things dopamine, focus, motivation, et cetera. Deliberate cold exposure has a very powerful effect on the release of dopamine in our brain and body, and this is one of the main reasons why people continue to do deliberate cold exposure. Basically, it makes us feel good and it continues to make us feel good even after we get out of the cold environment. In fact, some people would say they don't feel good in the cold environment, it's all stress for them, but afterwards they feel great. One of our previous guests, Dr. Anna Lembke, who's a medical doctor at Stanford University School of Medicine, she's a close colleague of mine, described the use of dopamine in her book, Dopamine Nation, an incredible book about addiction and dopamine, I should mention, and the use of dopamine elicited by cold water e- exposure by one of her patients. What I'm referring to is the fact that one of her patients helped themselves get and stay sober off drugs by using deliberate cold exposure to increase dopamine, so a healthier form of dopamine release than they were engaged in prior to getting sober. Now, the basis for dopamine release and response to cold exposure is that the catecholamines, norepinephrine, epinephrine, and dopamine tend to be co-released by the same sorts of stimuli, but most stressors, and in particular things that evoke stress or our feelings of stress internally that we don't like, do not increase dopamine. They only increase norepinephrine and epinephrine, but deliberate cold exposure seems to cause a dramatic increase in dopamine, and this has actually been substantiated in a really beautiful study entitled Human Physiological Responses to Immersion into Water of Different Temperatures. The first author is Sramek. I'm almost certainly pronouncing that poorly, if, and if not incorrectly, S-R-A-M-E-K. This was published in the European Journal of Applied Physiology in the year 2000. Really a beautiful study. I love this study. They took people and they had them sit in chairs underwater, but their head was out and they were, so they were immersed up to the neck in either three different, either of three different temperatures, excuse me, 32 degrees Celsius, which is 89 degrees Fahrenheit, 20 degrees Celsius, which is 68 degrees Fahrenheit, or 14 degrees Celsius, which is 57.2 degrees Fahrenheit. So not super cold, but then what they did is they measured people's core body temperature throughout, they measured their metabolism, and they looked at serum levels of things like norepinephrine, epinephrine, dopamine, and cortisol, serum meaning within the blood. So a really nice and quite thorough study. There were not a huge number of subjects in this study, but nonetheless, it was a very thorough study in terms of the number of variables that they explored. So I just want to briefly highlight some of what they saw or what they observed in this study. First of all, all the groups were in the water of a given temperature for one hour, which is much longer than most of the deliberate cold exposure protocols that anyone is using at home. I mean, maybe you're taking one-hour-long cold showers, maybe you're getting into the ice bath for an hour, although I don't recommend that. I think you'd probably get badly hypothermic. Or maybe you're getting into a cold water immersion for some period of time, but I have a hard time imagining that it would be an hour and I don't suggest that if it's very cold. So this study focused on actually somewhat moderately cool temperatures, not what I think most people would consider very, very cold temperatures, but extended the duration for quite a while. So again, 32 degrees Celsius, 20 degrees Celsius, or 14 degrees Celsius. Here's what they observed. The group that was immersed up to the neck in 32 degrees Celsius, that is 89 degrees Fahrenheit, water did not experience a shift in metabolism nor a significant increase in dopamine, norepinephrine, or these other catecholamines. The group that was in 20 degrees Celsius, meaning 68 degree Fahrenheit water for an hour experienced a 93% increase in metabolic rate, which is remarkable given that the water wasn't that cold, and yet an hour is a pretty long time to be in there. And again, it speaks to the dramatic effect of heat transfer that water has, which I mentioned earlier, as opposed to being out in the air at 68 degrees. It would n- certainly not cause that increase in metabolic rate.The group that was at 14 degrees Celsius, meaning 57.2 degrees Fahrenheit water for an hour, experienced a 350% increase in metabolism. So huge increases in metabolism. Now, the most interesting data to me, at least in terms of mental effects of deliberate cold exposure, were that the plasma or serum levels of norepinephrine in the blood increased 530%. These are huge increases in norepinephrine, so it suggests that this is a stressful stimulus, at least neurochemically speaking, stressful, despite the fact that it's not super, super cold. Although 57.2 degrees Fahrenheit, 14 degrees Celsius is not a, you know, it's not a warm environment, but it's not a ultra, ultra cold environment. But an hour is a very long time to be in there. The subjects also experienced a 250% increase in dopamine concentrations, which while not 530% as it was with norepinephrine, is still a very large increase in baseline levels of dopamine. And what was interesting is that those increases in dopamine persisted for a very long period of time afterwards, even out to two hours, okay? And they did, they stopped the study after 120 minutes of getting out of the, uh, cold, but nonetheless, these increases in norepinephrine are huge and long-lasting, and these increases in dopamine are very large and long-lasting. And I do believe that these documented effects in humans explain much of the enhancement of attention and of feelings of well-being and mood that people typically experience after doing deliberate cold exposure. And the reason I say that is that if you were to go back to the episode that I did on dopamine or you were to go back to the episode that I did with Dr. Anna Lembke on addiction and dopamine, what you would find is that increases in dopamine of the sort evoked by deliberate cold exposure are actually very similar to the kinds of increases in dopamine that are elicited by things like nicotine or from other behaviors that are known to be addictive and bad for us because they lead to other effects on the brain and body that we simply don't want. And yet deliberate cold exposure, provided it's done safely, can create similar if not greater increases in dopamine that are not just fleeting, that don't just occur during, say, the consumption of some deleterious drug or- or activity, but that are very long-lasting and that can be leveraged toward activities other than deliberate cold exposure. So I want to emphasize this, I'm not suggesting that people do deliberate cold exposure for an hour a day and unfortunately, there are not many studies yet exploring how shorter, colder t- temperature environment exposure, say, one minute or three minutes or six minutes at, you know, 55 degrees or at, um, 50 degrees, whether or not that leads to similar greater or reduced levels of dopamine in the brain and body. And yet almost everybody who does deliberate cold exposure will say, "Yeah, it was stressful. I didn't enjoy it," or, "I eventually grew to like it, but that I always feel better afterwards and then that feeling lasts a very long period of time." And I think it's almost certain that those experiences that people report relate to these increases in dopamine and in concert with the increases in norepinephrine also explain the other effect that's commonly reported which is an enhancement in mental acuity and the ability to focus. Now here we can extrapolate to the study that I discussed at the early part of the episode where I was talking about the use of short, 15-minute exercise, kind of moderate intensity exercise and how that was shown to increase levels of energy and mental acuity in these working memory visual attention tasks. And there again, we have to assume somewhat because they weren't doing neurochemical measurements, but we can reasonably assume that those improvements in cognitive performance were due at least in part to the increase in catecholamines known to accompany moderate intensity zone two cardio. So what you're starting to see here is a theme. The theme is that virtually any stimulus that delivers more norepinephrine, epinephrine, and dopamine to our system will sharpen our mental acuity and elevate our mood and will do so for some period of time. Deliberate cold exposure, it turns out, is a very potent way to increase these catecholamines, this category of chemicals, and thereby to improve mood, mental acuity, and levels of alertness, and as we'll s- next see, it not only has that effect which can be very beneficial for many people in a bunch of different circumstances, but it also has the positive effects that many people seek in terms of metabolism, in lowering inflammation in the body, and other physiological effects as well. And forgive me, I was almost ready to move on to effects of deliberate cold exposure on metabolism and inflammation and so forth, but I neglected to point out one of the other very interesting aspects of the study showing deliberate cold exposure can increase norepinephrine and dopamine, which is that they observed no significant increases in the stress hormone cortisol. And that is both surprising, interesting, and important because what it means is that the quality of stress that deliberate cold exposure is creating in the body is likely to be one of what we call eustress. Hans Selye, the great physiologist, won a Nobel Prize for distinguishing between distress, which is stress in the brain and body that causes the release of things like cortisol along with the other catecholamines and that we experience as negative happening to us and can lead to negative health outcomes, and he distinguished that from eustress, which was stress that we now understand is associated with increases in things like norepinephrine and dopamine but no increases or minimal increases in cortisol and that can lead to positive health outcomes. So it appears that deliberate cold exposure-... can create what we call, or what Hans Selye called, eustress. In other words, it can create a condition in the brain and body in which we are stressing ourselves, we are training up resilience, and yet we are creating a neurochemical milieu that actually has many

Andrew Huberman 1:12:55 health benefits. Now I'd like to shift our attention to the effects of deliberate cold exposure on metabolism, and I'd like to start by detailing a study that was performed on humans and published just at the end of last year. The title of the study is Altered Brown Fat Thermoregulation and Enhanced Cold-Induced Thermogenesis in Young Healthy Winter-Swimming Men. And I should point out that while the study was only performed on male subjects, there's no reason to think that the effects that they discovered would only pertain to men. I would hope that they would also do a study on women at some point in the future. But the effects that they describe are very basic core physiological processes. What they did is they looked at deliberate cold exposure in this group of young men, and they used that 11-minute threshold per week. So in other words, they had them get into cold water for approximately 11 minutes per week, and again, that's 11 minutes total per week. They divided that into two sessions, although in speaking with the first author of the study, Dr. Susanna Søberg, I learned that it probably is not important that it be two sessions, it could be three or even four sessions, as long as it reaches that 11-minute threshold. What they discovered was that by going into these cold environments, in this case, cold water immersion up to the neck for 11 minutes total per week, that these men experienced increases in so-called brown fat thermogenesis, I'll talk more about what that is in a moment, and increases in core body temperature that translate to increases in core body metabolism. Now, the overall increases in core body metabolism that they experienced were not extremely large. Uh, they were statistically significant, but they weren't extremely large. However, the changes in brown fat stores are perhaps what's most interesting about this study, and I'll tell you why. The metabolic increases of deliberate cold exposure are both acute, meaning happening in the short term, when you get into the cold and immediately after, one does experience an increase in core metabolism. You burn some calories, in other words. And while those might not be very significant increases, or I should say, they can be statistically significant, but they are not enormously large numbers of calories burned, the longer lasting effects of deliberate cold exposure on metabolism seem to take place by changes that occur in the types of fat that we store in our body and the way that that fat impacts our metabolism at other times throughout the 24-hour cycle. This actually has a somewhat anecdotal basis, in particular, in Scandinavia. I don't speak Swedish nor I speak Danish, nor do I speak Norwegian, but I do have Danish relatives, and they were able to help me decipher a, uh, common Swedish saying, which essentially translates to the fact that in preparation for the summer, they say, "One should expose themselves to warm environments so that one is comfortable in warm environments in the summer." That's one half of this traditional Swedish, and also Danish, saying. The other half of this traditional Danish-Swedish saying is that in preparation for winter, in order to not feel too cold in cold environments, one should prepare for those in the fall by not wearing a jacket and exposing oneself to cold environments. Now, of course, this is just anecdotal cultural lore, but it actually has a physiological basis, which is by exposing oneself to cold environments on a repeated basis in anticipation of exposure to more extreme cold environments, one can feel more comfortable in those extreme cold environments. And that's exactly what they observed in this study by Søberg et al., the men felt more comfortable in extreme cold if they had trained through deliberate cold exposure, which might not seem surprising at all, but b- based on what we talked about earlier, whereby deliberate cold exposure evokes this discomfort and this experience of norepinephrine release, at least in the short term, then you would say, "Well, shouldn't that deliberate cold exposure also make them feel uncomfortable, like they really want to get out?" Well, that is true at the beginning of a deliberate cold exposure protocol, meaning in the first week or in the second week or the third week. But what one finds and what you will find, if you do deliberate cold exposure consistently, is that you will then become more comfortable at cold temperatures away from the deliberate cold exposure. So whereas you might have previously been the person who was always cold in the room with air conditioning or always seeking a sweater, always wanting to bundle up, you will be more comfortable in those cold environments. And the reason for that is well-substantiated from this study and from animal studies, whereby deliberate cold exposure converts one particular kind of fat cell, the white fat cell, which is a very low metabolic output cell, it's basically a storage site for energy in the body, fat cells, to a different type of fat cell, which is the beige fat cell, called beige because it's actually beige or slightly brown under the microscope, or even to brown fat cells, which are very dark under the microscope, and dark because they contain me- mitochondria and are very metabolically and thermogenically active. In other words, white fat doesn't burn many calories. It's basically a storage site. It's a bank account for energy. It's filled with...... lipids, and those lipids can be used if the body needs energy and if it goes into a caloric deficit. Beige fat and brown fat acts as sort of a furnace or the sort of fat that you would find in a candle, a fuel that can increase core body temperature. So beige fat and brown fat is very good at raising our metabolism and helps burn white fat. Now, of course, it does that only in the context of a caloric deficit, but it can actually help create that caloric deficit. Having more beige fat and brown fat can increase your overall core metabolism, in other words, the number of calories that you burn per day, and therefore the number of calories that you need to either maintain or to lose weight. The simple translation of this is that getting into cold water for a total of 11 minutes, perhaps more, but at least 11 minutes per week, divided into two or four sessions, can increase your core metabolism in part by increasing your beige and brown fat stores. And we know how that works, at least in animal models, and there's now reason to suspect that the exact same mechanisms are occurring in humans. The primary way in which deliberate cold exposure converts white fat cells into these more metabolically, thermogenically active, metabolism increasing beige and brown fat cells is because norepinephrine released when we get into the cold binds to receptors on the surface of white fat cells and activates downstream pathways such as UCP1, so this is an Uncoupling Protein 1 that acts on the mitochondrial metabolism of cells and increases the mitochondrial output of those cells and the mitochondrial density of those cells. In other words, it takes a cell that has a kind of a weak engine or no engine for generating energy, although every cell has some mitochondria, it takes cells that have very few mitochondria and increases the engine size. It kind of stokes the furnace of those particular cells and actually can change gene expression in those cells. So that's what's really interesting. Deliberate cold exposure causes increases in norepinephrine, which bind to receptors on the surfaces of white fat cells, which triggers the release of things like UCP1. It also causes the release of things like PPAR-gamma and cofactor PGC-1. I'm going to refer you to a review if you want to learn more about these. For those of you that don't want to learn more, all you need to know is that the downstream of all that are increases in mitochondria and metabolism and actual genetic changes in the white fat cells that convert them into beige and brown fat cells. This is especially important for adults, because babies and young children actually don't have the ability to shiver or they have a less robust capacity to shiver. Very small babies really can't shiver, so they have a lot of brown fat in order to keep them warm. Young children eventually develop the ability to shiver and maintain these brown fat stores mainly around the clavicles, the heart, the upper spine, and in the upper back. And it's no coincidence that kids can often run around with a minimal of clothing and be comfortable in environments that adults would be cold in. As life goes on, we tend to lose beige and brown fat, but this mechanism that I'm referring to points to the plasticity of white fat, meaning the ability for white fat to actually convert its identity into this metabolically, thermogenically enhancing form of beige and brown fat. So deliberate cold exposure is a terrific way to increase your core metabolism, and oftentimes critics will say, "Well, the increase in metabolism isn't that significant," although I do want to point out again the 93% and 350% increases in metabolism from that previous study. But critics then will say, "Well, that doesn't really translate to that big of a caloric burn during the deliberate cold exposure." But to that you should say, "Ah, but that's only limiting your optics to just a portion of the effects of c- deliberate cold exposure, because deliberate cold exposure can also convert white fat to beige fat and brown fat and lead to these more lasting increases in metabolism." So for any of you interested in increasing your metabolism and/or being comfortable in cold environments and/or being comfortable in terms of being able to combat stress mentally, deliberate cold exposure I do believe is a powerful tool, and there is simply no reason why you couldn't and shouldn't use the same protocols that I described earlier for building resilience to increase metabolism. Provided you're hitting that 11 minute per week threshold, you ought