Benefits of Sauna & Deliberate Heat Exposure | Huberman Lab Essentials

0:00 Welcome to Huberman Lab Essentials,

0:01 [music] where we revisit past episodes for the most

0:04 potent and actionable science-based tools for mental health,

0:08 physical health, and performance.

0:11 I'm Andrew Huberman, and I'm a professor of neurobiology

0:14 and ophthalmology at Stanford School of Medicine.

0:17 Today, we are talking about the science of heat.

0:20 Heat is a remarkable stimulus, meaning when we are in a hot environment,

0:25 it has a profound effect on our biology.

0:28 So, we're going to talk about the science

0:29 of heat and heating both in terms of their mechanisms

0:33 and as I know many of you are interested

0:35 in, the tools related to the use of heat.

0:38 Things like sauna, how often to do sauna, how long to be in the sauna,

0:43 how hot to be in the sauna for particular goals and outcomes.

0:47 We heat up two ways.

0:49 We heat up from the outside, meaning the things that we come into contact

0:53 with, the clothing that we put on our body,

0:56 whether or not there's heat in the room or whether

0:59 or not it's cold outside or cold in the room, and we heat up from the inside.

1:04 At every point across your entire lifespan, you have two distinct temperatures.

1:09 One is the temperature on your skin, what scientists call your shell,

1:13 and the temperature of your core, your viscera,

1:17 meaning your organs, your nervous system, and your spinal cord.

1:20 It is vitally important to understand that you have those two

1:24 temperatures and that your brain is constantly sending out signals

1:27 to your body as to whether or not it should heat

1:30 up or cool down depending on the temperature of the shell.

1:34 So, anytime we're talking about heat, meaning deliberate heat exposure,

1:37 things like sauna, it's very important to understand not just the stimulus,

1:42 how hot something is, how long you're in a sauna, etc.,

1:45 but the effect that has on your shell and on your core.

1:49 If you can understand that, you can design

1:51 protocols that are literally perfect for your goals.

1:55 A brief warning now and another brief warning later.

1:58 Anytime you're talking about heating up your body,

2:01 you need to be very cautious because unlike cooling down where you have a fairly

2:06 broad range of cold temperatures that you

2:07 can go into before it's damaging to tissue,

2:10 well, you don't get to heat up the brain and body

2:13 very much before you start getting into the realm of neuron damage.

2:17 And neurons in the central nervous system,

2:19 the brain and spinal cord, once they're damaged, they don't come back.

2:22 So, hyperthermia is a serious thing to avoid.

2:24 There's a very basic circuit,

2:26 meaning neurons that exist in the skin, in the brain,

2:30 and in the body that communicate with one another that allow you

2:34 to heat up if you need to and cool down if you need to.

2:36 Once you understand this circuit and the way it's structured,

2:39 then you are going to be in a great

2:41 position to use the tools related to heating.

2:43 So, here's how this circuit is structured.

2:45 You have this shell, which is basically skin,

2:48 and within the skin you have neurons, nerve cells.

2:51 Those nerve cells have channels or receptors on them.

2:55 They're called trip channels.

2:56 There are some other ones as well, which basically sense changes in heat.

3:01 So, if I were to put a hot object on your hand or your arm, or for instance,

3:06 if I were to put a hot object

3:08 on your hand or arm and then remove that hot object,

3:11 those neurons would respond to that.

3:13 They would send electrical signals into your spinal cord.

3:16 And that's where the next station of this circuit resides.

3:19 In your spinal cord, you've got a little cluster of neurons that exists

3:22 at the top part of your spinal cord called the dorsal horn.

3:26 The name again doesn't matter.

3:27 And those neurons specifically relay heat information

3:30 up to another area of your brain.

3:32 Now, here's where we get into some fancy names.

3:34 It's the lateral parabrachial area.

3:37 You don't need to know lateral parabrachial area, but it's a relay station.

3:41 The lateral parabrachial area sends electrical signals to the POA.

3:45 And I would like you to know POA.

3:47 The POA stands for preoptic area.

3:50 Neurons in the preoptic area basically reside over the roof of your mouth.

3:54 These are neurons within the hypothalamus.

3:56 And neurons in the preoptic area have

4:00 the ability to send signals out to the rest of your brain and body to get you

4:05 to heat up and actually to change your behavior.

4:08 So, there are all these different mechanisms by which we dump heat.

4:12 Some of those are purely physiological, below our conscious control,

4:16 things like sweating, which you can't just make yourself sweat on demand.

4:21 Maybe you can through a set of stressful thoughts,

4:23 but you can't just make yourself sweat.

4:26 That is autonomic.

4:27 It's below your conscious control.

4:29 Things like vasodilation,

4:31 the dilation of your veins in particular and capillaries in particular.

4:36 And of course, there are these behavioral,

4:39 somewhat voluntary aspects of dumping heat.

4:42 And the lethargy, the kind of tiredness that we feel on a really hot day,

4:46 that's also controlled by the circuit that I just described.

4:49 The impulse to get yourself out of a very hot

4:52 environment is the consequence of the POA communicating with your amygdala.

4:57 And the amygdala then in turn activating your adrenal glands,

5:00 which are sit right above your kidneys,

5:02 the release of adrenaline, and this feeling of agitation like you want to move.

5:06 Usually, you want to move out of whatever hot environment you happen to be in.

5:10 So, now you know the circuit.

5:11 Again, it's simple.

5:12 It goes from skin to spinal cord, one brain area to another brain area.

5:16 That's the key one in this discussion, which is the POA, the preoptic area.

5:20 If you can conceptualize that circuit,

5:22 or if you can even just understand what I just said,

5:24 even at a top contour level,

5:26 you're going to be in a great position to understand

5:28 the rest of the information and the tools that follow.

5:31 The use of deliberate heat exposure can be

5:33 a very powerful way to improve health and longevity.

5:37 There's a wonderful study on this that was published in 2018 that includes

5:42 a lot of data from a lot of participants in a lot of different conditions.

5:46 For instance, people that only did sauna once versus two to three times a week

5:50 versus four to seven times a week and so on and compares all those.

5:53 The title of the study is "Sauna Bathing Is Associated

5:56 With Reduced Cardiovascular Mortality and Improves

5:59 Risk Prediction in Men and Women: A Prospective Cohort Study." This is one

6:05 of several papers that clearly demonstrate that regular

6:09 use of sauna or other forms of deliberate

6:11 heat exposure can reduce mortality to cardiovascular events,

6:16 but also to other events,

6:18 things like stroke and other things that basically can kill us.

6:22 What I like so much about this and the related

6:24 studies is that they involve a lot of participants.

6:27 So, for instance, in this particular paper, which was published in BMC Medicine,

6:30 they looked at a sample of 1,688 participants.

6:36 Who had a mean age of 63, but there was a range of ages around 63.

6:41 And of whom 51.4% were women, the rest were men.

6:44 So, it's a pretty nicely varied study

6:46 in terms of the populations that they looked at.

6:49 Basically, what they found was the more often that people do sauna,

6:54 the better their health is and the lower the likelihood

6:57 they will die from some sort of cardiovascular event.

7:00 Now, what do we mean by sauna?

7:01 We need to define some of the parameters around sauna and I promise

7:05 to provide you some alternative ways to access

7:08 some of the health benefits that were

7:10 observed in this and related studies without the need to have a sauna

7:14 cuz I do realize that a lot of people don't have access to sauna.

7:18 First off, the temperature ranges that were used in this study

7:20 and pretty much all the studies that I'm going to talk about,

7:23 unless I say otherwise, are between 80° C,

7:27 meaning 176° F, and 100° C, meaning 212° F.

7:35 So, somewhere in that range.

7:37 How hot should you make the sauna or the environment

7:40 that you get into should you decide to use these tools?

7:43 Well, that will depend on your tolerance for heat, how heat adapted you are.

7:48 Yes, some people are better at sweating than others

7:50 and over time we all get better at sweating.

7:52 Meaning if you go into the sauna more frequently, you become a better sweater.

7:57 Not a sweater you wear, but the verb, sweater.

7:59 You get better at sweating, at dumping heat through the loss of water.

8:03 So, it's going to depend.

8:05 I recommend starting on the lower end of the temperature scale and if

8:08 that's too hot for you that you even lower the temperature further.

8:11 Now, how long were people exposing themselves to these hot environments?

8:16 Anywhere from 5 to 20 minutes per session.

8:19 In this particular study,

8:20 they compared the effects of people that did sauna once a week,

8:24 two or three times per week, or four to seven times per week.

8:28 What they observed was that people who went

8:30 into the sauna two or three times per week were 27%

8:34 less likely to die of a cardiovascular event than

8:37 people that went into the sauna just once a week.

8:39 And today we're mainly going to talk about

8:41 exposures between 10 and 20 minutes at temperatures between,

8:46 again, 80° and 100° C, 176° F, or 212° F.

8:51 And in fact, And in fact, the benefits were even greater for people that were

8:53 going into the sauna four to seven times per week.

8:56 Those people were 50% less likely to die of a cardiovascular event

9:01 compared to people that went into the sauna just once a week.

9:04 What's particularly nice about this study and the related study

9:07 is that they looked at a number of potentially confounding variables.

9:11 Things like whether or not people smoked,

9:13 things like whether or not people were overweight,

9:14 whether or not they tended to exercise or not exercise,

9:18 and they were able to separate out those variables.

9:20 So, the percentages that I described earlier,

9:22 those effects really do seem to be the consequence of the sauna

9:26 exposure and not some other effect that's correlated with sauna exposure,

9:30 like going to the gym where people are working out seven

9:33 times a week and then also happen to get into the sauna,

9:35 or quitting smoking right about the same time they adopt a sauna protocol,

9:40 these sorts of things.

9:41 And now there have been additional analyses

9:43 of the use of sauna for improving health,

9:45 or I should say for offsetting mortality,

9:48 that have found that it's not just reductions in cardiovascular events,

9:52 but so-called all-cause mortality.

9:54 This is kind of medical geek speak for saying how

9:58 likely are you or somebody to die from a cardiovascular event,

10:02 but maybe also from some other event,

10:05 some other health-related event, like cancer or something of that sort.

10:09 And in every case, regular exposure to sauna,

10:12 starting at about two or three times per week,

10:14 all the way up to seven times per week,

10:16 greatly improves, meaning statistically significant improvements

10:21 in longevity in the sense that they people

10:24 are less likely to die of cardiovascular events and other things that kill us.

10:29 You don't have to use a sauna in order to get these benefits.

10:34 It is simply a matter of making sure

10:36 that your shell and your core heat up properly.

10:41 Not too much, not too little, but they heat those up.

10:44 So, the question is, how are you heating up your environment?

10:46 And I realize that there are dry saunas,

10:49 there are steam saunas, there are infrared saunas,

10:52 there are hot tubs, and there are simply rooms that you crank up the heat, okay?

10:59 There are also ways in which you can increase your shell and your core

11:02 temperature by moving around a lot and doing that wearing a lot of clothing.

11:07 There's nothing special about any one of these approaches or protocols.

11:12 It's just so happens that sauna is one of the more convenient ways to do this.

11:16 And certainly for the studies that I've talked about,

11:19 not just the ones I referenced before,

11:20 but all the studies that I researched looking at this episode,

11:24 it makes sense why they would use sauna because it's very hard, for instance,

11:28 to create conditions where you have, you know,

11:30 five people go out jogging wearing heavy sweaters and hats,

11:34 wool hats on the middle of summer, it's very hard to set up those conditions

11:38 in a way that's controlled for everybody.

11:39 Whereas, it's pretty straightforward to have a sauna where you have

11:42 one or several people just get into that one uniformly hot environment.

11:46 That's a much easier study to run.

11:48 You could, however, immerse yourself in a hot

11:51 tub or hot water bath up to your neck.

11:53 That's another way to approach it.

11:55 If you didn't have access to either of those, you could

11:58 also put on a hoodie or a wool hat and a hoodie,

12:04 or you could do like the wrestlers do,

12:06 and you could actually buy one of these plastic suits.

12:08 They're literally called plastics that uh wrestlers or other athletes that wish

12:12 to drop water weight will wear and then go jogging in that.

12:15 All of those will increase your shell and your core body temperature, right?

12:18 Especially if you do it on a hot day, but of course, be careful, hydrate,

12:20 and don't overheat, don't become excessively

12:22 hyperthermic cuz you can get heat stroke, and you can potentially die.

12:26 So, what happens when you get into a hot environment?

12:29 What are the mechanisms that allow for the various health effects of that?

12:32 So, blood flow increases,

12:33 plasma volume of your blood increases, and stroke volume,

12:38 the volume of blood that is mobilized

12:41 with each beat of your heart also increases,

12:44 and your heart rate increases to anywhere between 100 to 150 beats per minute.

12:49 That general constellation of effects looks a lot like cardiovascular exercise.

12:55 And in fact, for all intents and purposes, it really is cardiovascular exercise,

13:00 except that there isn't the mobilization and the loading

13:03 of joints and limbs and things of that sort.

13:06 And of course, there are additional benefits of cardiovascular

13:08 exercise that relate to impact on the ground,

13:13 improvements in bone density, etc., etc.

13:15 But, basically, your heart starts beating, more blood starts circulating,

13:19 your vasculature changes shape literally to accommodate

13:22 those increases in heart rate and blood volume,

13:26 and you're basically getting a cardiovascular workout in that hot environment,

13:30 even if you're just sitting down.

13:32 Another set of positive effects related to being

13:35 in these hot environments are hormone effects.

13:39 Shifts in the output of hormones both from your adrenals

13:42 and possibly from the testes and ovaries and even within the brain.

13:46 One of the more striking examples of that comes

13:49 from a study that was published in 2021.

13:53 The title of the study is endocrine effects of repeated

13:56 hot thermal stress and cold water immersion in young adult men.

14:00 And indeed, the study was in this case just done on men.

14:03 I'll just briefly describe the protocol they used.

14:05 They had these men attend four sauna sessions of 12 minutes each.

14:10 So again, well within that range of 5 to 20 minutes, 12 minutes.

14:14 The temperature of those saunas was 90 to 91° C.

14:18 That's 194° F, and they did that four times.

14:23 Afterwards, they had a 6-minute cool-down break,

14:26 during which they did get into some cool water or cold water of about 10°,

14:31 which is 10° C is 50° F.

14:35 And then they measured hormones at various times throughout this study,

14:39 before, during, and after.

14:40 The major effect of this study is

14:42 a significant decrease in cortisol output in these subjects.

14:47 I think this is really interesting

14:48 and important because many people suffer from acute,

14:51 meaning immediate, and long-term stress and are

14:53 looking for ways to control their stress.

14:55 Controlling your cortisol is tricky.

14:57 Many people are overworked.

14:59 They're overstressed.

15:00 For one reason or another,

15:01 they're subjected to many too many stressors or their level of stress resilience

15:06 isn't high enough to keep their cortisol levels clamped at a healthy level.

15:10 So the protocol I described of 12-minute

15:13 exposures to 90° environment, that's again 90° C,

15:17 followed followed by a 6-minute cool-down break in cool water, 50° or so.

15:23 That's pretty cold.

15:25 I can imagine that you could also just

15:26 take a cool shower or a cold shower afterwards.

15:29 That had a very significant effect on lowering cortisol.

15:32 So, there you have a tool that's not a completely zero-cost tool cuz you need

15:35 to heat the water and you need to have access to hot and cold water,

15:38 at least hot and cold contrast of some sort,

15:40 but it's fairly minimal cost for most people,

15:44 especially if you start getting creative about maybe taking a 12-minute

15:47 jog wearing a lot of clothing if it's hot out,

15:50 then getting into a cool shower.

15:51 You might not get the same extreme or significant reduction

15:55 in cortisol that was observed here with these very specific protocols,

15:58 but it's likely that you would get a similar result overall.

16:01 So, if you're seeking to use sauna to reduce stress, I think this is a very

16:05 interesting and potentially useful research-backed protocol.

16:08 And again, we will provide a link to the paper

16:11 if you'd like to read more about the data.

16:13 One of the more dramatic and important effects of going into a hot environment

16:18 for some period of time is the activation

16:21 of so-called heat shock proteins or HSPs.

16:24 Heat shock proteins are a protective mechanism in your brain

16:27 and body to rescue proteins that would otherwise misfold.

16:33 Now, what do I mean by this?

16:33 Well, most of you are familiar with the fact

16:36 that you have protein in the kitchen,

16:38 like a steak or a piece of chicken or a piece of fish,

16:41 and you heat it up, it changes its texture, right?

16:44 Raw meat is different than cooked meat.

16:46 Heat changes the quality of proteins, not just in terms of how they taste,

16:50 but the way in which they are configured.

16:53 It changes it right down at the molecular level.

16:55 When your body goes through changes in temperature

16:58 in response to hot environments or cold environments,

17:01 heat shock proteins are deployed to go and rescue and prevent

17:05 the changes in proteins that would be detrimental to your health.

17:09 So, at least in the short term, activating heat shock proteins is a good thing.

17:13 You don't want heat shock proteins to be activated for long

17:15 periods of time because that gets to be problematic for other reasons.

17:19 But, these heat shock proteins, of which there are many varieties,

17:22 basically have the job of traveling in your brain

17:24 and body and making sure that cells

17:27 that contain proteins that are misfolding because

17:30 they got heated up too much don't misfold.

17:33 And they also serve a protective mechanism,

17:36 making sure that proteins within the cells of your brain

17:39 and body don't fold in the wrong ways.

17:42 Um again, I'm describing this in very general terms,

17:44 but it's well established in animal models and in humans that sauna

17:49 exposure of the sort that I

17:50 described earlier activates these heat shock proteins.

17:53 There have been interesting studies done in humans examining

17:57 some of the downstream molecular pathways of deliberate heat

17:59 exposure that point to the mechanisms by which deliberate

18:03 heat exposure can help protect against different forms of mortality,

18:07 improve health overall, and possibly,

18:09 and I want to highlight possibly, possibly extend life.

18:14 One such mechanism involves a genetic program involving a molecule called FOXO3.

18:20 FOXO3 is a very interesting molecule

18:22 because it's involved in DNA repair pathways.

18:26 DNA repair is part of the process of remaining healthy.

18:30 You know, we'd all like to think that we're born and based on the genes we have,

18:35 we are healthy, healthy, healthy, then eventually we age and then we die.

18:39 But, from the time we're born until the time we die,

18:41 there's a constant repair of our proteins in our cells

18:44 and they modification of the genes that are being expressed.

18:47 You know, puberty being the most dramatic example, right?

18:50 You see a kid before puberty and after puberty looks like a different kid,

18:53 sounds like a different kid, thinks like a different kid.

18:54 In fact, basically is a different human being, right?

18:57 It's not just the hormones, it's that hormones themselves have the capacity

19:00 to turn on and turn off certain genes,

19:03 literally converting certain tissues and cells in the brain

19:06 and body to do entirely different things.

19:08 And DNA, the stuff of genes, gets damaged in that process.

19:13 FOXO3 sits upstream in a pathway related to DNA

19:18 repair and again clearing of these senescent cells.

19:22 Sauna exposure in particular sauna exposure two

19:26 to three times or ideally four to seven times per week in that 80 to 100° C

19:33 range has been shown to upregulate levels of FOXO3.

19:38 FOXO3 in turn upregulates pathways related to DNA repair

19:42 and clearing out of these senescent or dead cells

19:45 which is known to be important for various aspects

19:48 of maintaining cognition and other aspects of maintaining health.

19:52 So, these are the likely biological mechanisms for the improvements

19:58 in lifespan or I rather I should say these are

20:02 the biological mechanisms that apparently offset some of the cardiovascular

20:07 risk and other forms of mortality that were described earlier.

20:10 One especially interesting thing about FOXO3 there

20:14 are individuals out there that have either additional

20:18 copies of FOXO3 or who have versions of FOXO3 that are hyperactive so to speak.

20:25 Those people tend to be 2.7 times more likely

20:30 to live to 100 years of age or longer.

20:33 So, these are people that were just naturally

20:35 and fortunately for them endowed with more FOXO3,

20:38 more clearance of senescent cells, more DNA repair, etc.

20:42 Deliberate heat exposure is one way that you can increase FOXO3 activity.

20:47 There is no sauna protocol designed specifically to reduce cortisol

20:51 or specifically to increase FOXO3

20:54 or specifically to activate heat shock proteins.

20:57 Any deliberate heat exposure is likely to impact all of those mechanisms.

21:01 Again, I encourage you to use this guide

21:03 of 80 to 100° C as your kind of bookends for what you can tolerate and where you

21:10 want to start and eventually transition to in terms

21:14 of deliberate heat exposure and I would encourage

21:17 you to use that 5 to 20 minutes per session for the sauna as your rough

21:23 guide of how long to remain in the sauna.

21:25 Now I'd like to talk about the use of sauna to increase growth hormone.

21:29 Growth hormone impacts metabolism and growth of cells and tissues of the body.

21:34 It is responsible for tissue repair as well and the growth

21:38 spurt that everyone experiences during puberty

21:40 is the consequence of growth hormone.

21:43 What I'm about to describe is a study that found dramatic,

21:48 really dramatic I should say, increases in growth hormone but I also want

21:52 to emphasize that these increases in growth hormone were not

21:55 of the sort that are observed in puberty

21:57 or in infants becoming adolescents or adolescents growing into teenagers.

22:01 Those levels of growth hormone that are

22:03 associated with those massive transper- formations,

22:05 excuse me, of body morphology, of shape,

22:09 are far greater than the sorts that I'm talking about here and yet

22:14 as all of us age when we go from adolescents to their teenage

22:19 years and then into young adulthood but then starting in our early 30s

22:22 or so the amount of growth hormone that we secrete is greatly diminished.

22:28 Normally we would release growth hormone every

22:30 night after we go to sleep in particular in the early part of the night when

22:34 our sleep is comprised mostly of slow wave sleep.

22:37 As we age less growth hormone is released during that slow wave sleep.

22:42 Certain forms of deliberate heat exposure using sauna can stimulate very

22:46 large increases in growth hormone output which for people in their 30s,

22:49 40s and beyond could be very useful and may also be useful

22:53 for people who are just trying to stimulate the release of more

22:55 growth hormone in order to for instance recover from exercise or stimulate

22:59 fat loss or muscle growth or repair of a particular injury.

23:02 The title of this paper is endocrine effects of repeated sauna bathing.

23:06 And this is a paper that was published in 1986, which is some years ago,

23:10 but nonetheless serves as a basis for a lot of other studies that followed.

23:14 They used an 80° C environment, so that's 176° F.

23:19 They had subjects do this sauna for 30 minutes four times per day.

23:24 So, that's 2 hours total in 1 day.

23:27 30 minutes in the sauna, a period of cool down rest,

23:30 30 minutes in the sauna again, cool down rest, a third and a fourth time, okay?

23:33 So, 2 hours total in this 80° C environment.

23:37 So, that's a lot, but what they observed was really quite significant.

23:42 And I should mention they had both male and female subjects in this study.

23:46 And the entire study lasted a week.

23:48 They did this 2 hours of sauna exposure on day 1, day 3, and day 7 of that week.

23:54 And they measured a lot of different hormones.

23:56 I'll just cut to the chase and tell you the effects on growth hormone.

24:00 In subjects that did this 2-hour a day

24:02 80° C protocol experienced 16-fold increases in growth hormone.

24:09 So, they measured growth hormone before the sauna and after the sauna,

24:12 and growth hormone levels went up 16-fold, which is obviously an enormous

24:18 and it turns out statistically significant effect.

24:21 One important caveat here.

24:23 Remember earlier when I talked about people who did sauna once a week

24:27 versus two to three times a week versus four to seven times a week,

24:30 and the more often people did sauna, the less likely they were to die

24:34 of cardiovascular events or other things of that sort?

24:37 Well, in this case, the effects of sauna exposure on growth hormone

24:41 actually went down the more often that people did this deliberate heat exposure.

24:46 So, as I mentioned, they did this 2-hour

24:48 a day divided into 30-minute sessions protocol on day 1,

24:51 day 3, and day 7 of a week.

24:55 And what they found was on day one,

24:57 there was a 16-fold increase in growth hormone.

25:00 On day three, however, there was still a significant effect

25:04 on growth hormone as compared to before sauna,

25:07 but that effect was basically cut by 2/3.

25:11 Okay, so now instead of getting a 16-fold increase,

25:14 it was more like a three or fourfold increase, which is still a huge increase,

25:19 but not as great as the increase observed on day one.

25:22 And then on day seven, there tended to be a two,

25:24 maybe a three-fold increase, but not as great as the one observed on day one.

25:30 The fact that that result diminished over time either means that the circuit

25:33 was not as efficient in communicating

25:35 that shift in temperature or that that shift

25:38 in temperature was of less impact because the downstream effectors were not

25:43 engaged to the same extent because it wasn't as much of a shock.

25:46 And I think the latter explanation is far more likely.

25:48 This is very much akin to weight training or cardiovascular

25:52 exercise where if you run up a hill very fast,

25:54 for instance, and your lungs are burning and you're heaving and breathing hard,

25:59 on the first day, that's a very painful thing.

26:01 But if you do it every day or every other day,

26:03 provided you allow yourself to recover,

26:05 pretty soon you're running up that hill and you're not breathing as hard.

26:08 There isn't much burning in your muscles, etc., etc.

26:11 Your body adapts.

26:13 So if you're going to use deliberate heat exposure

26:14 in order to try and trigger massive increases in growth hormone,

26:17 you're going to need to be careful about not doing it more than,

26:20 let's say, once a week.

26:21 Now, I'm extrapolating from this study.

26:23 Maybe once every 10 days would be even better.

26:26 But if you start getting heat adapted, it's very unlikely that you're going

26:31 to get these massive increases in growth hormone.

26:33 So I don't mean to be discouraging of using

26:35 deliberate heat exposure to access growth hormone increases,

26:39 but if that's your specific goal or your main goal,

26:42 then I think it's reasonable to say

26:44 that you don't want to do deliberate heat exposure,

26:46 at least not of the sort that I described here,

26:48 more than once a week or maybe even once every 10 days.

26:51 And that you would want to time that to other events in your life,

26:54 maybe hard workouts, or if you're trying to push through a fat loss barrier,

26:59 or simply in order to access growth hormone at peak levels,

27:03 maybe three times per month, or four times per month.

27:06 If you start doing deliberate heat exposure more often,

27:08 you'll still get increases in growth hormone,

27:10 but they are not going to be nearly

27:12 as large as the increases in growth hormone that you're

27:15 going to experience if you shock your system

27:18 with the deliberate heat exposure every once in a while.

27:21 When you decide to do sauna,

27:23 or cold exposure for that matter, is going to be important.

27:26 Why?

27:26 Well, if you were to make the surface of your body cold,

27:29 at least in the immediate period

27:31 after that, your body temperature will increase.

27:34 And that can make it hard for some people to fall asleep.

27:36 Now, if you're very,

27:37 very tired because you've been working hard, or training hard,

27:40 or both throughout the day, it might not throw off your sleep so much.

27:43 I've gone through bouts where I'm just so,

27:45 so busy from morning till night that the only time I can get into the ice bath,

27:48 or the cold shower, is late in the evening,

27:50 and I have no trouble sleeping after that.

27:51 If you're going to use deliberate heat exposure,

27:54 you'd be wise to do it later in the day

27:56 because when you get into a warm environment, sure,

27:59 the surface of your body, the shell, heats up, the core of your body heats up,

28:04 but then it also activates cooling mechanisms through the preoptic area.

28:09 And when you get out of that hot environment,

28:11 sauna or otherwise, your body will continue to cool down,

28:15 and so many people find that if they do sauna in the later half of the day,

28:18 or even just before sleep, and then take a warmish shower afterwards,

28:23 then they find it easier to fall asleep,

28:25 and that makes sense because their body temperature is dropping.

28:28 And in fact, if your goal is to really

28:30 promote the maximum amount of growth hormone release,

28:33 that's also going to be the best time of day to do it,

28:35 especially if you haven't eaten in the two hours before sleep.

28:39 Okay?

28:39 So, if you're really going for growth hormone release,

28:41 you're really trying to optimize sleep,

28:42 and the two things are actually linked because of the release of growth

28:45 hormone that happens from the pituitary in the early night's sleep, well,

28:49 then you would be wise to do your sauna

28:51 maybe once or maybe twice a week in the evening

28:54 or at night time then taking a warm

28:56 or cool shower just briefly just enough to kind

28:59 of rinse off all the sweat from the sauna and then get ready for sleep and to do

29:03 that not necessarily fasted but to try and keep

29:07 your levels of glucose and insulin somewhat low in your bloodstream.

29:10 The reason I say that is that having

29:12 elevated blood glucose and or insulin tends to blunt

29:17 or reduce growth hormone release and that's true for any

29:20 number of different stimuli including exercise and including sauna.

29:24 If you really want to crank out the most

29:26 amount of growth hormone in response to sauna,

29:28 do it fasted or at least not having ingested

29:30 any food in the two or three hours before.

29:33 You don't have to be deep into a fast.

29:35 I think for 90% of people 90% of the time just getting into the sauna

29:40 once or twice or three times a week is going to be beneficial for the number

29:44 of reasons that I described earlier and you don't want to obsess too much about

29:49 the exact conditions you need in order to get

29:51 the greatest effect out of that sauna treatment.

29:53 Now, regardless of what time of day you do sauna or how frequently you do it,

29:57 you're going to want to hydrate after going in the sauna.

30:01 When you go in the sauna,

30:02 you lose water and when you lose water, you need to replace it.

30:06 Why?

30:06 Well, you need water for all your cells but you also need electrolytes.

30:09 So, make sure that you're replacing the water that you lose in the sauna.

30:13 Now, there's no exact formula of how much water to drink

30:15 and whether or not you need electrolytes in that water or not.

30:18 It's going to depend on how much you sweat meaning how heat adapted you are.

30:21 It's going to depend on how much salt you tend to excrete in your sweat.

30:24 Huge amount of variation but in general,

30:27 one way to approach this would be to make sure that you drink at least

30:30 16 oz of water for every 10 minutes that you happen to be in the sauna.

30:36 You could do that before and during and after.

30:38 You could do it during and after or you could do it after.

30:41 Now, there are other reasons to do deliberate heat

30:43 exposure that have improvements in mood and mental health.

30:47 In fact, the data related to sauna and other

30:51 forms of deliberate heat exposure improving mood are

30:53 very impressive both at the mechanistic level

30:56 and in terms of the long-term consequences that people experience.

31:00 First of all, we need to ask how is it

31:02 that deliberate heat exposure can improve our mood and well-being?

31:05 Well, it turns out that it improves mood and well-being,

31:08 but it also improves our capacity to feel good in response

31:13 to things that would ordinarily make us feel somewhat good.

31:17 Now, this is not a situation where

31:19 you're going to be walking around grinning ear

31:21 to ear in response to nothing at all simply because you went in a sauna.

31:25 What I'm talking about is the up-regulation of pathways,

31:29 meaning chemical pathways in your brain and body

31:32 that allow you to experience pleasure in all its fullness.

31:35 Many of you have probably heard of endorphins.

31:37 Endorphins are a category of molecules that are made naturally in your brain

31:41 and body and that are released in response to different forms of stressors.

31:46 That's right, in response to stressors.

31:48 So, if ever you've gone out on a long run and at some

31:50 point that run you feel like you're aching and your joints hurt

31:53 or maybe you have shin splints and you push through that, part

31:57 of the reason that you experience a lack of pain at some point,

32:01 usually, or you experience a euphoria during or after

32:05 that exercise is the exercise-induced effects on endorphin release.

32:10 Or rather, to be more specific,

32:12 I should say the exercise-induced consequences on the stress system,

32:16 which in turn trigger the release of endorphin.

32:19 In other words, when we experience short-term or acute stress,

32:24 the endorphin system is activated.

32:26 Now, the endorphin system is not just about feeling good.

32:30 Believe it or not, it's also about feeling bad.

32:32 And there are two general categories of endorphins.

32:34 The first are the ones that you normally hear about, endorphins,

32:38 things that bind for instance to receptors like the mu opioid receptor.

32:42 We make endorphins that naturally act as pain

32:45 relievers and that make us feel mildly euphoric.

32:48 We also make endorphins such as dynorphin, that's d y n o r p h i n,

32:55 dynorphin, that actually make us feel worse in response to stressors.

33:01 When we get into a hot sauna or a hot environment of any kind,

33:06 dynorphins are liberated in the brain and body.

33:09 And I should mention that dynorphins are made

33:11 by many neurons in many different areas of the brain.

33:14 So you might think, well, why would I want that?

33:16 Why would I want to release dynorphin into my brain and body?

33:19 Well, first of all, when you get into an uncomfortably hot situation,

33:22 uncomfortably hot scenario, oh gosh, this is sounding terrible.

33:25 A a deliberately hot environment that you are using to try

33:30 and trigger some sort of biological or psychological benefit, I should say.

33:34 The discomfort that you feel, the desire to get out of the that environment,

33:38 is in part the consequence of the release of dynorphin.

33:42 It's also the consequence of the activation of that sympathetic nervous system.

33:46 Remember, the preoptic area can communicate with the amygdala

33:49 and trigger that kind of fight or flight mode.

33:51 I want to get out of the sauna, this is really really hot.

33:53 But dynorphin is also liberated from a certain number of neurons.

33:57 Dynorphin binds to what's called the kappa receptor.

34:01 The kappa receptor binds dynorphin and triggers pathways

34:05 in the brain and body that lead to agitation,

34:08 to stress, and believe it or not, to a general sense of pain.

34:12 This is why you want to get out of the hot sauna.

34:14 And remember, if it's unsafe levels of hot,

34:17 then you should get out of that sauna or other hot environment.

34:20 But if you're working in a range or you're exposing yourself to a range

34:24 of heat that's uncomfortable but safe to be

34:26 in, dynorphin will be liberated from these neurons, bind to to kappa receptor,

34:31 and as a downstream consequence of that, there will be

34:35 an increase in the receptors that bind the other endorphins.

34:39 The endorphins that make you feel soothed,

34:41 that make you feel happy, and that make you feel mild euphoria.

34:45 It's fair to say that every time we get

34:46 into a hot environment that's uncomfortable

34:48 or a cold environment that's uncomfortable,

34:50 dynorphin is likely released and binding to the kappa receptor.

34:55 But over time, that binding of dynorphin to the kappa receptor

34:59 leads to downstream changes in the way that the feel-good endorphins,

35:03 things like endorphin binding to the mu opioid receptor,

35:06 and there are still other feel-good endorphins, so to speak.

35:10 That system becomes much much more efficient,

35:13 such that people feel an elevation in their baseline level of mood,

35:16 and when a good or happy event comes along,

35:20 they feel a heightened level of happiness or joy

35:23 or awe or improved mood in response to that.

35:26 So, what does it mean?

35:27 It means that a little bit of discomfort

35:30 as a consequence of deliberate heat exposure,

35:32 while in the short term doesn't feel good by definition,

35:36 it is activating pathways that are allowing the feel-good molecules and neural

35:41 circuitries that exist in your brain and body to increase their efficiency,

35:45 placing you in a better position to be joyful in response to the events of life.

35:50 We're starting to see a general picture that using the sorts

35:53 of sauna protocols that I've described throughout this episode, right?

35:57 5 to 20 minutes or so, done one to seven times per week,

36:02 is associated with a general improvement in cardiovascular health,

36:07 a general improvement in mental health.

36:10 And it really points to the fact that yes,

36:12 sauna done acutely for three or four times a day,

36:16 30 minutes each session separated by a cooling,

36:19 maybe getting into cold bath, sure, that can potently increase growth hormone.

36:23 But done on a more regular basis can reduce cortisol,

36:26 improve heart health, improve mental health.

36:29 And for that reason and the fact

36:31 that for most people it is conceivable to come up

36:34 with a way that you could get into deliberate

36:36 heat exposure for a minimum of cost, right?

36:38 It's a hot bath or if you had to resort to, you know,

36:41 bundling up and going for a jog, this sort of thing or if you have access to it,

36:45 a sauna of some sort that we're really

36:48 talking about a stimulus to initiate a large

36:52 number of different biological cascades that wick out

36:55 to improve multiple aspects of brain and body health.

36:59 Each protocol that I've talked about today,

37:01 whether or not it's 5 minutes or 20 minutes or four times

37:03 in a day or three times per week or seven times per week,

37:06 is tickling or pushing or stomping, if you will,

37:10 on a given pathway and really activating it to a milder to severe degree.

37:14 What I've tried to do today is to illustrate

37:16 the general mechanisms by which heat, in particular,

37:20 can activate certain biological pathways so that you can devise protocols

37:24 that are going to be optimal for you and your needs.

37:27 So, just to briefly recap,

37:29 if you want to get the greatest growth hormone increases,

37:32 do sauna or other deliberate heat exposure fairly seldom.

37:37 Probably no more than once per week, maybe even less.

37:40 And do it a lot that day,

37:41 just make sure that you break it up into multiple sessions.

37:43 In the study I described earlier, they did four sessions, 30 minutes each.

37:47 But that was just once a week.

37:50 If you're interested in the cardiovascular benefits

37:53 and the potential longevity benefits of sauna,

37:55 well, then it's clear that doing it three to four,

37:57 maybe even seven times per week is going to be more

37:59 of beneficial than doing it just one or three times per week.

38:02 And again, that range of 80 to 100° C is going to be your guide.

38:07 And in terms of the mental health benefits,

38:09 it seems that getting a little bit uncomfortable in that heat environment,

38:12 sauna or otherwise, provided safe, is going to be the best way to access

38:17 those mental health effects by way of increasing dynorphin,

38:21 which, as you recall,

38:22 will then increase the ability of endorphin to have its positive effects

38:27 on mood after you get out of the sauna or other deliberate heat exposure.

38:31 And in terms of timing, after a workout of any kind,

38:35 morning or afternoon, or if you're not doing it after a workout,

38:39 certainly in the later part of the day is

38:41 going to be most beneficial as it relates to sleep.

38:43 But, of course, there's a caveat there, which I will mention again,

38:46 which is that for those of you that have no trouble

38:48 sleeping because you're exhausted or you're

38:49 just one of these phenomenal sleepers, well, then do it anytime of day or night.

38:54 But, for most people, doing it later in the day is going

38:56 to be more beneficial because of the post-sauna cooling

38:59 effect and the relationship between cooling by a degree

39:02 or more as a way to enter sleep.

39:05 Thank you for joining me today for my discussion

39:07 about the science of heat and heating for health.

39:11 And last, but certainly not least, [music]

39:13 thank you for your interest in science.