Benefits of Sauna & Deliberate Heat Exposure | Huberman Lab Essentials

Welcome to Huberman Lab Essentials, [music] where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health, and performance. I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. Today, we are talking about the science of heat. Heat is a remarkable stimulus, meaning when we are in a hot environment, it has a profound effect on our biology. So, we're going to talk about the science of heat and heating both in terms of their mechanisms and as I know many of you are interested in, the tools related to the use of heat. Things like sauna, how often to do sauna, how long to be in the sauna, how hot to be in the sauna for particular goals and outcomes. We heat up two ways. We heat up from the outside, meaning the things that we come into contact with, the clothing that we put on our body, whether or not there's heat in the room or whether or not it's cold outside or cold in the room, and we heat up from the inside. At every point across your entire lifespan, you have two distinct temperatures. One is the temperature on your skin, what scientists call your shell, and the temperature of your core, your viscera, meaning your organs, your nervous system, and your spinal cord. It is vitally important to understand that you have those two temperatures and that your brain is constantly sending out signals to your body as to whether or not it should heat up or cool down depending on the temperature of the shell. So, anytime we're talking about heat, meaning deliberate heat exposure, things like sauna, it's very important to understand not just the stimulus, how hot something is, how long you're in a sauna, etc., but the effect that has on your shell and on your core. If you can understand that, you can design protocols that are literally perfect for your goals. A brief warning now and another brief warning later. Anytime you're talking about heating up your body, you need to be very cautious because unlike cooling down where you have a fairly broad range of cold temperatures that you can go into before it's damaging to tissue, well, you don't get to heat up the brain and body very much before you start getting into the realm of neuron damage. And neurons in the central nervous system, the brain and spinal cord, once they're damaged, they don't come back. So, hyperthermia is a serious thing to avoid. There's a very basic circuit, meaning neurons that exist in the skin, in the brain, and in the body that communicate with one another that allow you to heat up if you need to and cool down if you need to. Once you understand this circuit and the way it's structured, then you are going to be in a great position to use the tools related to heating. So, here's how this circuit is structured. You have this shell, which is basically skin, and within the skin you have neurons, nerve cells. Those nerve cells have channels or receptors on them. They're called trip channels, there are some other ones as well, which basically sense changes in heat. So, if I were to put a hot object on your hand or your arm, or for instance, if I were to put a hot object on your hand or arm and then remove that hot object, those neurons would respond to that. They would send electrical signals into your spinal cord. And that's where the next station of this circuit resides. In your spinal cord, you've got a little cluster of neurons that exists at the top part of your spinal cord, called the dorsal horn. The name again doesn't matter. And those neurons specifically relay heat information up to another area of your brain. Now, here's where we get into some fancy names. It's the lateral parabrachial area. You don't need to know lateral parabrachial area, but it's a relay station. The lateral parabrachial area sends electrical signals to the POA. And I would like you to know POA. The POA stands for preoptic area. Neurons in the preoptic area basically reside over the roof of your mouth. These are neurons within the hypothalamus. And neurons in the preoptic area have the ability to send signals out to the rest of your brain and body to get you to heat up and actually to change your behavior. So, there are all these different mechanisms by which we dump heat. Some of those are purely physiological, below our conscious control, things like sweating, which you can't just make yourself sweat on demand. Maybe you can through a set of stressful thoughts, but you can't just make yourself sweat. That is autonomic. It's below your conscious control. Things like vasodilation, the dilation of your veins in particular and capillaries in particular. And of course, there are these behavioral, somewhat voluntary aspects of dumping heat. And the lethargy, the kind of tiredness that we feel on a really hot day, that's also controlled by the circuit that I just described. The impulse to get yourself out of a very hot environment is the consequence of the POA communicating with your amygdala. And the amygdala then in turn activating your adrenal glands, which are sit right above your kidneys, the release of adrenaline, and this feeling of agitation like you want to move. Usually, you want to move out of whatever hot environment you happen to be in. So, now you know the circuit. Again, it's simple. It goes from skin to spinal cord, one brain area to another brain area. That's the key one in this discussion, which is the POA, the preoptic area. If you can conceptualize that circuit, or if you can even just understand what I just said, even at a top contour level, you're going to be in a great position to understand the rest of the information and the tools that follow. The use of deliberate heat exposure can be a very powerful way to improve health and longevity. There's a wonderful study on this that was published in 2018 that includes a lot of data from a lot of participants in a lot of different conditions. For instance, people that only did sauna once versus two to three times a week versus four to seven times a week and so on and compares all those. The title of the study is "Sauna Bathing Is Associated With Reduced Cardiovascular Mortality and Improves Risk Prediction in Men and Women: A Prospective Cohort Study." This is one of several papers that clearly demonstrate that regular use of sauna or other forms of deliberate heat exposure can reduce mortality to cardiovascular events, but also to other events, things like stroke and other things that basically can kill us. What I like so much about this and the related studies is that they involve a lot of participants. So, for instance, in this particular paper, which was published in BMC Medicine, they looked at a sample of 1,688 participants who had a mean age of 63, but there was a range of ages around 63. And of whom 51.4% were women, the rest were men. So, it's a pretty nicely varied study in terms of the populations that they looked at. Basically, what they found was the more often that people do sauna, the better their health is and the lower the likelihood they will die from some sort of cardiovascular event. Now, what do we mean by sauna? We need to define some of the parameters around sauna and I promise to provide you some alternative ways to access some of the health benefits that were observed in this and related studies without the need to have a sauna because I do realize that a lot of people don't have access to sauna. First off, the temperature ranges that were used in this study and pretty much all the studies that I'm going to talk about, unless I say otherwise, are between 80° C, meaning 176° F, and 100° C, meaning 212° F. So, somewhere in that range. How hot should you make the sauna or the environment that you get into should you decide to use these tools? Well, that will depend on your tolerance for heat, how heat adapted you are. Yes, some people are better at sweating than others and over time we all get better at sweating. Meaning if you go into the sauna more frequently, you become a better sweater. Not a sweater you wear, but the verb, sweater. You get better at sweating, at dumping heat through the loss of water. So, it's going to depend. I recommend starting on the lower end of the temperature scale and if that's too hot for you that you even lower the temperature further. Now, how long were people exposing themselves to these hot environments? Anywhere from 5 to 20 minutes per session. In this particular study, they compared the effects of people that did sauna once a week, two or three times per week, or four to seven times per week. What they observed was that people who went into the sauna two or three times per week were 27% less likely to die of a cardiovascular event than people that went into the sauna just once a week. And today we're mainly going to talk about exposures between 10 and 20 minutes at temperatures between, again, 80° and 100° C, 176° F, or 212° F. And in fact, the benefits were even greater for people that were going into the sauna four to seven times per week. Those people were 50% less likely to die of a cardiovascular event compared to people that went into the sauna just once a week. What's particularly nice about this study and the related study is that they looked at a number of potentially confounding variables. Things like whether or not people smoked, things like whether or not people were overweight, whether or not they tended to exercise or not exercise, and they were able to separate out those variables. So, the percentages that I described earlier, those effects really do seem to be the consequence of the sauna exposure and not some other effect that's correlated with sauna exposure, like going to the gym where people are working out seven times a week and then also happen to get into the sauna, or quitting smoking right about the same time they adopt a sauna protocol, these sorts of things. And now there have been additional analyses of the use of sauna for improving health, or I should say for offsetting mortality, that have found that it's not just reductions in cardiovascular events, but so-called all-cause mortality. This is kind of medical geek speak for saying how likely are you or somebody to die from a cardiovascular event, but maybe also from some other event, some other health-related event, like cancer or something of that sort. And in every case, regular exposure to sauna, starting at about two or three times per week, all the way up to seven times per week, greatly improves, meaning statistically significant improvements in longevity in the sense that they people are less likely to die of cardiovascular events and other things that kill us. You don't have to use a sauna in order to get these benefits. It is simply a matter of making sure that your shell and your core heat up properly. Not too much, not too little, but they heat those up. So, the question is, how are you heating up your environment? And I realize that there are dry saunas, there are steam saunas, there are infrared saunas, there are hot tubs, and there are simply rooms that you crank up the heat, okay? There are also ways in which you can increase your shell and your core temperature by moving around a lot and doing that wearing a lot of clothing. There's nothing special about any one of these approaches or protocols. It's just so happens that sauna is one of the more convenient ways to do this. And certainly for the studies that I've talked about, not just the ones I referenced before, but all the studies that I researched looking at this episode, it makes sense why they would use sauna because it's very hard, for instance, to create conditions where you have, you know, five people go out jogging wearing heavy sweaters and hats, wool hats on the middle of summer, it's very hard to set up those conditions in a way that's controlled for everybody. Whereas, it's pretty straightforward to have a sauna where you have one or several people just get into that one uniformly hot environment. That's a much easier study to run. You could, however, immerse yourself in a hot tub or hot water bath up to your neck. That's another way to approach it. If you didn't have access to either of those, you could also put on a hoodie or a wool hat and a hoodie, or you could do like the wrestlers do, and you could actually buy one of these plastic suits. They're literally called plastics that uh wrestlers or other athletes that wish to drop water weight will wear and then go jogging in that. All of those will increase your shell and your core body temperature, right? Especially if you do it on a hot day, but of course, be careful, hydrate, and don't overheat, don't become excessively hyperthermic cuz you can get heat stroke, and you can potentially die. So, what happens when you get into a hot environment? What are the mechanisms that allow for the various health effects of that? So, blood flow increases, plasma volume of your blood increases, and stroke volume, the volume of blood that is mobilized with each beat of your heart also increases, and your heart rate increases to anywhere between 100 to 150 beats per minute. That general constellation of effects looks a lot like cardiovascular exercise. And in fact, for all intents and purposes, it really is cardiovascular exercise, except that there isn't the mobilization and the loading of joints and limbs and things of that sort. And of course, there are additional benefits of cardiovascular exercise that relate to impact on the ground, improvements in bone density, etc., etc. But, basically, your heart starts beating, more blood starts circulating, your vasculature changes shape literally to accommodate those increases in heart rate and blood volume, and you're basically getting a cardiovascular workout in that hot environment, even if you're just sitting down. Another set of positive effects related to being in these hot environments are hormone effects. Shifts in the output of hormones both from your adrenals and possibly from the testes and ovaries and even within the brain. One of the more striking examples of that comes from a study that was published in 2021. The title of the study is endocrine effects of repeated hot thermal stress and cold water immersion in young adult men. And indeed, the study was in this case just done on men. I'll just briefly describe the protocol they used. They had these men attend four sauna sessions of 12 minutes each. So again, well within that range of 5 to 20 minutes, 12 minutes. The temperature of those saunas was 90 to 91° C. That's 194° F, and they did that four times. Afterwards, they had a 6-minute cool-down break, during which they did get into some cool water or cold water of about 10°, which is 10° C is 50° F. And then they measured hormones at various times throughout this study, before, during, and after. The major effect of this study is a significant decrease in cortisol output in these subjects. I think this is really interesting and important because many people suffer from acute, meaning immediate, and long-term stress and are looking for ways to control their stress. Controlling your cortisol is tricky. Many people are overworked, they're overstressed. For one reason or another, they're subjected to many too many stressors or their level of stress resilience isn't high enough to keep their cortisol levels clamped at a healthy level. So the protocol I described of 12-minute exposures to 90° environment, that's again 90° C, followed followed by a 6-minute cool-down break in cool water, 50° or so, that's pretty cold. I can imagine that you could also just take a cool shower or a cold shower afterwards. That had a very significant effect on lowering cortisol. So, there you have a tool that's not a completely zero cost tool cuz you need to heat the water and you need to have access to hot and cold water, at least hot and cold contrast of some sort, but it's fairly minimal cost for most people, especially if you start getting creative about maybe taking a 12-minute jog wearing a lot of clothing if it's hot out, then getting into a cool shower. You might not get the same extreme or significant reduction in cortisol that was observed here with these very specific protocols, but it's likely that you would get a similar result overall. So, if you're seeking to use sauna to reduce stress, I think this is a very interesting and potentially useful research-backed protocol. And again, we will provide a link to the paper if you'd like to read more about the data. One of the more dramatic and important effects of going into a hot environment for some period of time is the activation of so-called heat shock proteins or HSPs. Heat shock proteins are a protective mechanism in your brain and body to rescue proteins that would otherwise misfold. Now, what do I mean by this? Well, most of you are familiar with the fact that you have protein in the kitchen, like a steak or a piece of chicken or a piece of fish, and you heat it up, it changes its texture, right? Raw meat is different than cooked meat. Heat changes the quality of proteins, not just in terms of how they taste, but the way in which they are configured. It changes it right down at the molecular level. When your body goes through changes in temperature in response to hot environments or cold environments, heat shock proteins are deployed to go and rescue and prevent the changes in proteins that would be detrimental to your health. So, at least in the short term, activating heat shock proteins is a good thing. You don't want heat shock proteins to be activated for long periods of time because that gets to be problematic for other reasons. But, these heat shock proteins, of which there are many varieties, basically have the job of traveling in your brain and body and making sure that cells that contain proteins that are misfolding because they got heated up too much don't misfold. And, they also serve a protective mechanism, making sure that proteins within the cells of your brain and body don't fold in the wrong ways. Um again, I'm describing this in very general terms, but it's well established in animal models and in humans that sauna exposure of the sort that I described earlier activates these heat shock proteins. There have been interesting studies done in humans examining some of the downstream molecular pathways of deliberate heat exposure that point to the mechanisms by which deliberate heat exposure can help protect against different forms of mortality, improve health overall, and possibly, and I want to highlight possibly, possibly extend life. One such mechanism involves a genetic program involving a molecule called FoxO3. FoxO3 is a very interesting molecule because it's involved in DNA repair pathways. DNA repair is part of the process of remaining healthy. You know, we'd all like to think that we're born and based on the genes we have, we are healthy, healthy, healthy, then eventually we age and then we die. But, from the time we're born until the time we die, there's a constant repair of our proteins in our cells and they modification of the genes that are being expressed. You know, puberty being the most dramatic example, right? You see a kid before puberty and after puberty, looks like a different kid, sounds like a different kid, thinks like a different kid. In fact, basically is a different human being, right? It's not just the hormones, it's that hormones themselves have the capacity to turn on and turn off certain genes, literally converting certain tissues and cells in the brain and body to do entirely different things. And, DNA, the stuff of genes, gets damaged in that process. FOXO3 sits upstream in a pathway related to DNA repair and again clearing of these senescent cells. Sauna exposure in particular sauna exposure two to three times or ideally four to seven times per week in that 80 to 100° C range has been shown to upregulate levels of FOXO3. FOXO3 in turn upregulates pathways related to DNA repair and clearing out of these senescent or dead cells which is known to be important for various aspects of maintaining cognition and other aspects of maintaining health. So, these are the likely biological mechanisms for the improvements in lifespan or I rather I should say these are the biological mechanisms that apparently offset some of the cardiovascular risk and other forms of mortality that were described earlier. One especially interesting thing about FOXO3 there are individuals out there that have either additional copies of FOXO3 or who have versions of FOXO3 that are hyperactive so to speak. Those people tend to be 2.7 times more likely to live to 100 years of age or longer. So, these are people that were just naturally and fortunately for them endowed with more FOXO3, more clearance of senescent cells, more DNA repair, etc. Deliberate heat exposure is one way that you can increase FOXO3 activity. There is no sauna protocol designed specifically to reduce cortisol or specifically to increase FOXO3 or specifically to activate heat shock proteins. Any deliberate heat exposure is likely to impact all of those mechanisms. Again, I encourage you to use this guide of 80 to 100° C as your kind of bookends for what you can tolerate and where you want to start and eventually transition to in terms of deliberate heat exposure and I would encourage you to use that 5 to 20 minutes per session for the sauna as your rough guide of how long to remain in the sauna. Now I'd like to talk about the use of sauna to increase growth hormone. Growth hormone impacts metabolism and growth of cells and tissues of the body. It is responsible for tissue repair as well and the growth spurt that everyone experiences during puberty is the consequence of growth hormone. What I'm about to describe is a study that found dramatic, really dramatic I should say, increases in growth hormone but I also want to emphasize that these increases in growth hormone were not of the sort that are observed in puberty or in infants becoming adolescents or adolescents growing into teenagers. Those levels of growth hormone that are associated with those massive transper formations, excuse me, of body morphology, of shape, are far greater than the sorts that I'm talking about here and yet as all of us age when we go from adolescents to their teenage years and then into a young adulthood but then starting in our early 30s or so the amount of growth hormone that we secrete is greatly diminished. Normally we would release growth hormone every night after we go to sleep in particular in the early part of the night when our sleep is comprised mostly of slow wave sleep. As we age less growth hormone is released during that slow wave sleep. Certain forms of deliberate heat exposure using sauna can stimulate very large increases in growth hormone output which for people in their 30s, 40s and beyond could be very useful and may also be useful for people who are just trying to stimulate the release of more growth hormone in order to for instance recover from exercise or stimulate fat loss or muscle growth or repair of a particular injury. The title of this paper is endocrine effects of repeated sauna bathing. And this is a paper that was published in 1986, which is some years ago, but nonetheless serves as a basis for a lot of other studies that followed. They used an 80° C environment, so that's 176° F. They had subjects do this sauna for 30 minutes four times per day. So, that's 2 hours total in 1 day. 30 minutes in the sauna, a period of cool down rest, 30 minutes in the sauna again, cool down rest, a third and a fourth time, okay? So, 2 hours total in this 80° C environment. So, that's a lot, but what they observed was really quite significant. And I should mention they had both male and female subjects in this study. And the entire study lasted a week. They did this 2 hours of sauna exposure on day 1, day 3, and day 7 of that week. And they measured a lot of different hormones. I'll just cut to the chase and tell you the effects on growth hormone. In subjects that did this 2-hour a day 80° C protocol experienced 16-fold increases in growth hormone. So, they measured growth hormone before the sauna and after the sauna, and growth hormone levels went up 16-fold, which is obviously an enormous and it turns out statistically significant effect. One important caveat here. Remember earlier when I talked about people who did sauna once a week versus two to three times a week versus four to seven times a week, and the more often people did sauna, the less likely they were to die of cardiovascular events or other things of that sort? Well, in this case, the effects of sauna exposure on growth hormone actually went down the more often that people did this deliberate heat exposure. So, as I mentioned, they did this 2-hour a day divided into 30-minute sessions protocol on day 1, day 3, and day 7 of a week. And what they found was on day one, there was a 16-fold increase in growth hormone. On day three, however, there was still a significant effect on growth hormone as compared to before sauna, but that effect was basically cut by 2/3. Okay, so now instead of getting a 16-fold increase, it was more like a three- or four-fold increase, which is still a huge increase, but not as great as the increase observed on day one. And then on day seven, there tended to be a two- maybe a three-fold increase, but not as great as the one observed on day one. The fact that that result diminished over time either means that the circuit was not as efficient in communicating that shift in temperature or that that shift in temperature was of less impact because the downstream effectors were not engaged to the same extent because it wasn't as much of a shock. And I think the latter explanation is far more likely. This is very much akin to weight training or cardiovascular exercise where if you run up a hill very fast, for instance, and your lungs are burning and you're heaving and breathing hard, on the first day, that's a very painful thing. But if you do it every day or every other day, provided you allow yourself to recover, pretty soon you're running up that hill and you're not breathing as hard. There isn't much burning in your muscles, etc., etc. Your body adapts. So, if you're going to use deliberate heat exposure in order to try and trigger massive increases in growth hormone, you're going to need to be careful about not doing it more than, let's say, once a week. Now, I'm extrapolating from this study. Maybe once every 10 days would be even better. But if you start getting heat adapted, it's very unlikely that you're going to get these massive increases in growth hormone. So, I don't mean to be discouraging of using deliberate heat exposure to access growth hormone increases, but if that's your specific goal or your main goal, then I think it's reasonable to say that you don't want to do deliberate heat exposure, at least not of the sort that I described here, more than once a week or maybe even once every 10 days. And that you would want to time that to other events in your life, maybe hard workouts or if you're trying to push through a fat loss barrier, or simply in order to access growth hormone at peak levels, maybe three times per month or four times per month. If you start doing deliberate heat exposure more often, you'll still get increases in growth hormone, but they are not going to be nearly as large as the increases in growth hormone that you're going to experience if you shock your system with deliberate deliberate heat exposure every once in a while. When you decide to do sauna or cold exposure for that matter, is going to be important. Why? Well, if you were to make the surface of your body cold, at least in the immediate period after that, your body temperature will increase. And that can make it hard for some people to fall asleep. Now, if you're very, very tired because you've been working hard or training hard or both throughout the day, it might not throw off your sleep so much. I've gone through bouts where I'm just so, so busy from morning till night that the only time I can get into the ice bath or the cold shower is late in the evening, and I have no trouble sleeping after that. If you're going to use deliberate heat exposure, you'd be wise to do it later in the day because when you get into a warm environment, sure, the surface of your body, the shell heats up, the core of your body heats up, but then it also activates cooling mechanisms through the preoptic area. And when you get out of that hot environment, sauna or otherwise, your body will continue to cool down, and so many people find that if they do sauna in the later half of the day or even just before sleep and then take a warmish shower afterwards, then they find it easier to fall asleep, and that makes sense because their body temperature is dropping. And in fact, if your goal is to really promote the maximum amount of growth hormone release, that's also going to be the best time of day to do it, especially if you haven't eaten in the 2 hours before sleep. Okay? So, if you're really going for growth hormone release, you're really trying to optimize sleep, and the two things are actually linked because of the release of growth hormone that happens from the pituitary in the early night's sleep, well, then you would be wise to do your sauna maybe once or maybe twice a week in the evening or at night time then taking a warm or cool shower just briefly just enough to kind of rinse off all the sweat from the sauna and then get ready for sleep and to do that not necessarily fasted but to try and keep your levels of glucose and insulin somewhat low in your bloodstream. The reason I say that is that having elevated blood glucose and or insulin tends to blunt or reduce growth hormone release and that's true for any number of different stimuli including exercise and including sauna. If you really want to crank out the most amount of growth hormone in response to sauna, do it fasted or at least not having ingested any food in the two or three hours before. You don't have to be deep into a fast. I think for 90% of people 90% of the time just getting into the sauna once or twice or three times a week is going to be beneficial for the number of reasons that I described earlier and you don't want to obsess too much about the exact conditions you need in order to get the greatest effect out of that sauna treatment. Now, regardless of what time of day you do sauna or how frequently you do it, you're going to want to hydrate after going in the sauna. When you go in the sauna, you lose water and when you lose water, you need to replace it. Why? Well, you need water for all your cells but you also need electrolytes. So, make sure that you're replacing the water that you lose in the sauna. Now, there's no exact formula of how much water to drink and whether or not you need electrolytes in that water or not. It's going to depend on how much you sweat meaning how heat adapted you are. It's going to depend on how much salt you tend to excrete in your sweat. Huge amount of variation but in general, one way to approach this would be to make sure that you drink at least 16 oz of water for every 10 minutes that you happen to be in the sauna. You could do that before and during and after. You could do it during and after or you could do it after. Now, there are other reasons to do deliberate heat exposure that have improvements in mood and mental health. In fact, the data related to sauna and other forms of deliberate heat exposure improving mood are very impressive both at the mechanistic level and in terms of the long-term consequences that people experience. First of all, we need to ask how is it that deliberate heat exposure can improve our mood and well-being? Well, it turns out that it improves mood and well-being, but it also improves our capacity to feel good in response to things that would ordinarily make us feel somewhat good. Now, this is not a situation where you're going to be walking around grinning ear to ear in response to nothing at all simply because you went in a sauna. What I'm talking about is the up-regulation of pathways, meaning chemical pathways in your brain and body that allow you to experience pleasure in all its fullness. Many of you have probably heard of endorphins. Endorphins are a category of molecules that are made naturally in your brain and body and that are released in response to different forms of stressors. That's right, in response to stressors. So, if ever you've gone out on a long run and at some point in that run you feel like you're aching and your joints hurt or maybe you have shin splints and you push through that, part of the reason that you experience a lack of pain at some point usually or you experience a euphoria during or after that exercise is the exercise induced effects on endorphin release. Or rather, to be more specific, I should say the exercise induced consequences on the stress system which in turn trigger the release of endorphin. In other words, when we experience short-term or acute stress, the endorphin system is activated. Now, the endorphin system is not just about feeling good. Believe it or not, it's also about feeling bad. And there are two general categories of endorphins. The first are the ones that you normally hear about, endorphins, things that bind for instance to receptors like the mu opioid receptor. We make endorphins that naturally act as pain relievers and that make us feel mildly euphoric. We also make endorphins such as dynorphin, that's d y n o r p h i n, dynorphin, that actually make us feel worse in response to stressors. When we get into a hot sauna or a hot environment of any kind, dynorphins are liberated in the brain and body. And I should mention that dynorphins are made by many neurons in many different areas of the brain. So you might think, well, why would I want that? Why would I want to release dynorphin into my brain and body? Well, first of all, when you get into an uncomfortably hot situation, uncomfortably hot scenario, oh gosh, this is sounding terrible. A a deliberately hot environment that you are using to try and trigger some sort of biological or psychological benefit, I should say. The discomfort that you feel, the desire to get out of the that environment is in part the consequence of the release of dynorphin. It's also the consequence of the activation of that sympathetic nervous system. Remember, the preoptic area can communicate with the amygdala and trigger that kind of fight or flight mode. I want to get out of the sauna, this is really really hot. But dynorphin is also liberated from a certain number of neurons. Dynorphin binds to what's called the kappa receptor. The kappa receptor binds dynorphin and triggers pathways in the brain and body that lead to agitation, to stress, and believe it or not, to a general sense of pain. This is why you want to get out of the hot sauna. And remember, if it's unsafe levels of hot, then you should get out of that sauna or other hot environment. But if you're working in a range or you're exposing yourself to a range of heat that's uncomfortable but safe to be in, dynorphin will be liberated from these neurons, bind to to kappa receptor, and as a downstream consequence of that, there will be an increase in the receptors that bind the other endorphins. The endorphins that make you feel soothed, that make you feel happy, and that make you feel mild euphoria. It's fair to say that every time we get into a hot environment that's uncomfortable or a cold environment that's uncomfortable, dynorphin is likely released and binding to the kappa receptor. But over time, that binding of dynorphin to the kappa receptor leads to downstream changes in the way that the feel-good endorphins, things like endorphin binding to the mu opioid receptor, and there are still other feel-good endorphins, so to speak. That system becomes much much more efficient, such that people feel an elevation in their baseline level of mood, and when a good or happy event comes along, they feel a heightened level of happiness or joy or awe or improved mood in response to that. So, what does it mean? It means that a little bit of discomfort as a consequence of deliberate heat exposure, while in the short term doesn't feel good by definition, it is activating pathways that are allowing the feel-good molecules and neural circuitries that exist in your brain and body to increase their efficiency, placing you in a better position to be joyful in response to the events of life. We're starting to see a general picture that using the sorts of sauna protocols that I've described throughout this episode, right? 5 to 20 minutes or so, done one to seven times per week, is associated with a general improvement in cardiovascular health, a general improvement in mental health. And it really points to the fact that yes, sauna done acutely for three or four times a day, 30 minutes each session separated by a cooling, maybe getting into cold bath, sure, that can potently increase growth hormone. But done on a more regular basis can reduce cortisol, improve heart health, improve mental health. And for that reason and the fact that for most people it is conceivable to come up with a way that you could get into deliberate heat exposure for a minimum of cost, right? It's a hot bath or if you had to resort to, you know, bundling up and going for a jog, this sort of thing, or if you have access to it, a sauna of some sort, that we're really talking about a stimulus to initiate a large number of different biological cascades that wick out to improve multiple aspects of brain and body health. Each protocol that I've talked about today, whether or not it's 5 minutes or 20 minutes or four times in a day or three times per week or seven times per week, is tickling or pushing or stomping, if you will, on a given pathway and really activating it to a milder to severe degree. What I've tried to do today is to illustrate the general mechanisms by which heat, in particular, can activate certain biological pathways so that you can devise protocols that are going to be optimal for you and your needs. So, just to briefly recap, if you want to get the greatest growth hormone increases, do sauna or other deliberate heat exposure fairly seldom. Probably no more than once per week, maybe even less. And do it a lot that day, just make sure that you break it up into multiple sessions. In the study I described earlier, they did four sessions, 30 minutes each. But that was just once a week. If you're interested in the cardiovascular benefits and the potential longevity benefits of sauna, well, then it's clear that doing it three to four, maybe even seven times per week is going to be more of beneficial than doing it just one or three times per week. And again, that range of 80 to 100° C is going to be your guide. And in terms of the mental health benefits, it seems that getting a little bit uncomfortable in that heat environment, sauna or otherwise, provided safe, is going to be the best way to access those mental health effects by way of increasing dynorphin, which, as you recall, will then increase the ability of endorphin to have its positive effects on mood after you get out of the sauna or other deliberate heat exposure. And in terms of timing, after a workout of any kind, morning or afternoon, or if you're not doing it after a workout, certainly in the later part of the day is going to be most beneficial as it relates to sleep. But, of course, there's a caveat there, which I will mention again, which is that for those of you that have no trouble sleeping because you're exhausted or you're just one of these phenomenal sleepers, well, then do it anytime of day or night. But, for most people, doing it later in the day is going to be more beneficial because of the post-sauna cooling effect and the relationship between cooling by a degree or more as a way to enter sleep. Thank you for joining me today for my discussion about the science of heat and heating for health. And last, but certainly not least, >> [music] >> thank you for your interest in science.