← The mindbodygreen Podcast
The mindbodygreen Podcast
642: The science of sweat, saunas & stress | best-selling author Bill Gifford
00:46:41
Bill Gifford, a veteran science journalist and author of Spring Chicken, a New York Times bestseller on longevity. His latest book, Hotwired: How the Hidden Power of Heat Makes Us Stronger, dives deep into the emerging science of heat, sweating, and what happens when we stop running from discomfort.
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Welcome to the MyBodyGreen podcast. I'm Jason Wakab, founder and co CEO of MyBodyGreen and your host. Rei has ultralight backpacking gear, so for you Graham counters and ounce shavers, we made this ad ultralight with a base
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weight of just 13 seconds.
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The next 17 seconds pure trailer. Find more with less in store and@rei.com whether you bond over streaming binge worthy videos, watching sports recaps, video gaming or by unplugging altogether, the 2026 Lincoln Nautilus Hybrid helps keep you connected throughout your journey. Learn more@lincoln.com available connectivity, features and functionality vary by model. Package pricing, trials and term lengths vary by model. Video streaming and games are only available while parked. What if one of the most powerful tools for your health has been hiding in plain sight and most of us have been actually avoiding it? Today's guest is Bill Gifford, a veteran science journalist, author of Spring Chicken, a New York Times bestselling author on longevity, and co author of Outlive. His latest book, how the Hidden Power of Heat Makes Us Stronger, dives deep into the emerging science of heat sweating and what happens when we stop running from discomfort. Bill spent his career translating cutting edge science for real people, writing for Wired, Bloomberg Businessweek, Scientific American, Outside, and more. In this episode, we get into why sweating is one of humanity's greatest evolutionary superpowers and what we lose when we live in perfectly climate controlled comfort. 247 we discussed the Finnish sauna tradition, what the science says about minimum effective dose, and why heat exposure may be one of the most underrated tools for cardiovascular and mental health. We also tackle the cold plunge debate. Bill makes a compelling case for why the cold side of the equation is far less settled than what one would believe. This one Challenges of my own assumptions, and I think it will challenge yours too. Let's dive in. Heat sweating. You argue that sweating, which many people do not like, is a superpower. Let's talk about that. What did we lose when we moved into this world of constant climate control? And how do we get it back when we reintroduce heat?
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B
Yeah, so our ability to sweat is this evolutionary anomaly and it kind of happened by accident, they think, more than a million years ago, the series of genetic mutations that took these existing sweat glands that our ancestors had in their feet and their, I guess, paws spread them all over their body. These are our prehuman like apelike ancestors.
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Right.
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So they had these all sudden they had these sweat glands all over their body and they lost their body here. So now they could sweat to cool themselves. And this meant that they could basically kick the butts of every other animal. They went from the middle of the food chain, started climbing to the top. Because now, because they could sweat and because we could sweat, they could function in the middle of the day in the heat of the day. In Africa on the equator, so all the other animals had to kind of hide in the shade, right? We could be out foraging, even hunting. We had it to ourselves. So sweating is our superpower. So we've been sweating for a million years. Air conditioning was invented in 1903, and it took decades to catch on. So even like our grandparents would have endured or not, or endured slashed, been able to handle 30, 40 degree temperature swings in the course of a day, heat, especially in North America, heat to cold, right? So we had this big temperature range and we're evolutionarily equipped to handle it. But now fast forward to the modern era, and we live in 67 degrees, 70, 72. Perfect comfort all the time.
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A
I'm sold. I live in Miami.
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B
That's not a bad thing necessarily. Like air conditioning is great to sleep in, I'll be honest. And you live in Miami, so, you
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A
know, I live in Miami. I'm sold. And yes, cold is great for sleep. That's fair to say. So if we say if we'll get into this heat versus the hot versus cold debate, but cold is good for sleep. So. But let's go into why is heat so good? Why is sweating so good for our health?
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B
It's one of those things where science has caught up to ancient customs. People have been doing saunas for thousands of years, literally sauna like practices. And many cultures around the world have these sort of hot spaces that people have gone into, you know, as a. But like a daily ritual. So, you know, it's sort of like with alcohol or wine, right? You know, we've been making wine for thousands of years. Fermenting beer does something that we kind of like, right? There must be something to it. So science has caught up to that and found that across a variety of systems and contexts, raising your body temperature a little bit, you know, a couple degrees Fahrenheit can do some good things to your physiology and then to your even cellular biology. So just for example, when you get into a hot sauna or when you go out and say, ride your bike in Miami, your heart rate accelerates, right? Because your body's trying to cool itself. It's trying to maintain this temperature homeostasis. So your heart rate speeds up. You have all this blood flow surging beneath the surface of your skin as, as it tries to send the hot blood to your skin to radiate heat and then start sweating. So you get a sort of a cardiovascular benefit from that. You get a, a vascular benefit from that. Your blood vessels dilate, right? And then at a deeper level you start activating certain stress resistance mechanisms in our cells that essentially are there to protect us from heat, but also may have potential health benefits and longevity benefits.
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A
So essentially this is a great example you're talking about. You're comparing sauna to essentially light cardio in terms of cardiovascular impact. Should we think of this as exercise adjacent, if you will, or substitute for exercise, like how far, how far? I'm with you there. But how far should we take this in terms of our protocol, our weekly protocol?
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B
It kind of depends where you're starting from, but it, it mimics some of the things that happen during exercise. Not crucially, not the muscle activation, right? So that's a big part of exercise and it's a whole other conversation. But it does accelerate heart rate and it does create, you know, you sweat just like, just like you do when you're, when you're exercising. It's not a substitute. But you, you know, you, you feel like you did something if you sit in a sauna, for example.
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A
So on that note, what's your view on minimum effective dose?
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B
That's a tricky question. A lot of people out there are kind of prescribing a certain protocol. And I think if you talk to the people who actually are deep into the sauna research, that's a big question that they haven't quite answered. There are some studies from Finland, the famous Finnish observational sauna studies that everybody talks about where they found that the guys, it was men originally who went every other day or every day and spent 19 minutes or more in 175 degrees or hotter sauna did the best across heart attack risk, stroke risk, all cause mortality, even Alzheimer's disease, and, and some other things that we can talk about. But that was based on a one time questionnaire that these guys filled out as part of a bigger cardiovascular risk, studying every aspect of their lives. So there was this one page of sauna questions and they answered them once when they were like 40, 50, and then they were followed for 20 years. But you know, I, I don't think you have a, a habit from 20 years ago that you're performing exactly the same way, right? So you know, it, it's not super solid, it's suggestive. But you know, other, other studies have, have found that there are some. Like for example, they found a increase in growth hormone in people who use sauna. That, that sounds great. But the people in this study, I think they did two or possibly three 30 minute sessions in a very hot sauna. So that's a, that's a, that's a commitment. Right? That's, that's an intense hot day to get that particular benefit. So the jury's, jury's out.
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A
So there's no gold standard study. Interesting. And so how does one. Okay. If we operate on the assumption we need to sweat some heat is good. We're all on board with raising heart rate. Sometimes heat exposure can look risky. How do people distinguish between this is productive hormetic stress versus overdoing it, Become chronically dehydrated and running into a whole host of other issues.
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B
Yeah, the dehydration thing is real. And you know, I experienced it with my partner when we went to Finland and you know, we got in these super hot like these were like big league saunas. This was not the minor leagues anymore. And it was so hot in there that like her earrings, she had to take her earrings out. I had to take my, you know, my, my garment was about to explode.
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Yeah. Yeah. You can't wear a wearable in there to melt.
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Yeah. Which is also awesome. So we did that like, oh, felt great. And you know, I had a couple beers afterwards and we, the next day we're walking around, I'm like, just like arguing and like feeling like crap or walking around Helsinki and just like, oh my God, what happened? She's like, I thought sauna was healthy and we didn't drink enough water like rookies. So hydrate. Hydration. That's a long way of saying hydration is really important if you're sweating to that degree. And also electrolytes like, you know sauna sweating is serious.
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Right.
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Hot yoga sweating is serious sweating. You have to pay attention to that. Now as to for how hot is too hot. Interestingly, if you're in a finish style sauna, I'll stick with that. Your core temperature actually doesn't go up that much. It's really interesting. Like your skin temperature gets hot. Especially when they do the steam thing, the Lola or the Loyly.
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Right.
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They throw the water on the rocks. This blast of steam comes up. Finish people love that. And it's like awesome. It's like the, it's like injected into my veins. It's this great feeling. But you have this intense heat on your Skin, your core doesn't, doesn't get that hot. Interestingly, that is like, what else?
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Like, the Finns have like the monopoly in all the studies, and it's just embedded into their.
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The Germans are coming on strong.
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Okay, what is it about the Finns? Like, what have you learned from them culturally as it relates to all things sauna? What are the takeaways?
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So the sauna was akin to like the bathtub. It's like where you went to get clean and it just happened to be. Since each person couldn't have an individual sauna, it was like a family thing. So you'd be in there with the whole family, sans clothes, and it was a weekly thing, or it was every few days, heat up the sauna and everybody would come in and, and, and get clean. That was really it. But it turned out to be this one of those customs that had like, I don't want to say scalability, but it had like all these other benefits that we're kind of exploring now. You know, interestingly, before the germ, we knew about germs, the Finns and Scandinavians and Russians and Ukrainians were going into these hot spaces that were hot enough to kill germs, right? So they, they gave birth in saunas, which is the craziest cultural fact. Imagine giving birth in a sauna. This was quite common. I've met people who were born in a sauna.
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And with regards to the sauna itself, have you developed a view on. You know, we talked about temperature, but is one type better than the next? What should, what should one consider if they're in the market for a sauna or just looking to get into one and try it out.
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What do you like doing? I mean, there's certain, there's an elementality to the. Is that a word? Elemental nature? To the finished sauna, where you have the rocks and water and steam and so it's kind of earthy. And wood, you know, it's super simple, right. The aesthetic is unfinished wood. And, you know, a lot of people like that infrared sauna, a little more modern high tech. It's not my cup of tea, personally, but it does the job and it actually does heat up your, your core a little bit more efficiently. But, you know, as far as, like, the health benefits, if that's your goal, almost any form of heat modality works. Even, you know, the humble, you know, the, the, the cheesy California hot tub works just fine and it gets your core temperature up nicely, you know, and they've even found that taking a hot Bath every day is quite sim, has effects quite similar, at least in the cardiovascular plane to these sauna studies. So taking a hot bath, you know, that works. Anything that gets you hot works.
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A
So in other words, as our listeners know and I mentioned, we live in Miami and it gets quite hot here kind of everywhere in the summer these days. And so my wife loves the sauna, regardless of what's going on, temperature wise. But I'll always joke, I don't need it. I'm just going to go for a walk. Maybe I'll throw on a vest or something, I'll sweat. I notice when I walk when it's very humid and hot, my heart rate, I wear a whoop. My heart rate will, you know, I'll, I'll get sometimes into like Zone 4 walking, when typically that's like not happening on any other day, like below 80, like I'm in like zone, I gotta work. Walk really fast to get into zone too. It's just like not happening. So am I experiencing benefits by saying like, hey, it's 2 o' clock and it's 103 in humid in Miami, I'm gonna go walk.
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B
So you're doing a different thing that's called basically heat acclimation training. And I explored that in the book as well. And that's a whole other fascinating topic. You know, now that the Olympics are being held in, in these hot places like Tokyo, for example, in Los Angeles, athletes, high level athletes have to do heat training. Tour de France riders have to do heat training or they just won't make it, they won't finish. And what is heat training? So think about like, I mean, you're in a interesting climate, but in most of the country, think about how like an 85 degree day feels in May versus how that same temperature might feel in August, right? In May it's brutal. And you're sweating, you know, sweating like crazy. In August you're like, oh, what a nice day. Right? And so that's because you've become heat adapted over the summer months just by being outside. And so what happens is your response to the heat changes. So initially you might have that high heart rate, you might be in Zone 4 on an easy exercise, but then you do that for. You do that four or five days out of the week for a couple weeks and then maybe your heart rate won't be quite as high on, in, on the same, same kind of day. So you become adapted. So your plasma volume expands, right? With heated adaptation, you, you begin to sweat sooner and you sweat more and Your sweat is less salty, so your sweat evaporates better. So your body's kind of tuning up its cooling system. And at the same time, in addition to your plasma volume expanding, you start making more red blood cells. Your hemoglobin increases so you have more oxygen. Comparing carrying capacity. So while you're walking along the beach in Miami on that hot day, you're actually, you're actually doing the same thing as altitude training. You're improving your aerobic capacity. So stick with it.
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I love it. It is, it's the same thing with altitude. Like whenever we go to like the mountains, for example, once a year, maybe go to Colorado or Salt Lake where you are. The altitude kicks my butt and it takes, it takes me probably a week and then I'm leaving anyway. I'm never, I don't go anywhere that long. I finally start to adjust. So same situation and equally as beneficial as we think about our well being.
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B
Yeah. And certainly there are performance benefits and health benefits attached to it. And just in terms of resilience. Right. Heat adaptation means that the next heat wave or hot spell is less taxing on you. And then that becomes relevant for athletes like football players, for example, but also for older people who are much more vulnerable, who are less flexible. Right. In terms of less thermally flexible, let's say. But with a little bit of heat adaptation, they can handle those hot days better.
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On that note, you mentioned athletes and you've spent time with elite athletes. What can we learn from how they train? Using heat to gain a competitive edge? What, what can us normal folks learn from these people?
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So for me, you know, I live in a hot place as well. It's, it's a hot and dry place. But you know, and I'm not a, I'm not a hot weather guy. At least I didn't think of myself as a hot weather person. I'm a winter sports guy. And so I kind of dreaded the summer. And so, and like I would not exercise as much in the summer. I wouldn't want to go out and ride my bike when it was 90 degrees or whatever. So learning these techniques of heat training sort of enabled me to, to be more comfortable with the climate. And so that was a big, a big benefit. And then as a result of that, I'm more comfortable exercising at different times of the day in the summer. So that, that's one, that's one benefit. So thereafter a performance benefit. But I think for a recreational athlete, probably like most people listening, there's a, there's a survival and Maybe survival benefit isn't quite the right word, but a resilience benefit, right? So let's say you're, I mean the Boston Marathon's a great example, right. It's held in April. It's, it's a few weeks away. And it can either be, it can be 50 degrees or it can be 75 degrees. And those are two totally different situations. And if you've been training all winter for Boston and Suddenly it's an 80 degree day that you've never experienced before in your training, you're in trouble. Right? Your poor performance is going to suffer. You might suffer, you might not finish. And so there's a case to be made for adding a little dose of heat training to your marathon training or to whatever else you happen to be training for.
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So speaking to that contrast at the gym I go to, you see lots of folks do hot, cold, they'll go in the steam or sauna, then they'll go to the plunge, then they'll go back to the steamer sauna, then they'll go back to the plunge. They'll do cycles of this. What's your view on hot cold? And then we'll segue to cold, which you've been I think critical of. But we'll start with hot gold just
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in a really super basic level like feels good after you've been in a hot sauna to then go dump some of that heat in either a cold plunge or you know, in a lot of sauna places in Finland they have a, a wooden bucket with a rope and you pull it and you dunk yourself. I like that. Right. So you're just bringing your temperature back to equilibrium.
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Right.
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You know the, the specific benefits of hot to cold, hot to cold. There's not super solid data on that. Those finish sauna studies I talked about earlier, you could assume that those people were doing the traditional, you know, do the sauna and then maybe jump in the lake or whatever. But it as far as like a specific protocol, it's not, it's not super well supported but it feels good. So people do it.
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A
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B
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A
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B
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A
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B
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A
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B
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- [22:34]
A
After three months, Plan Auto renews at $12.99 a month. Terms apply. Well, I don't do the hot cold, but I'll do the cold. And we'll segue to your criticisms of cold. But my understanding is if you are doing the hot cold, always finish on cold, not hot. Finishing on hot could be potentially dangerous. Oh, why too much of a shock if you're going back and forth and then finishing on hot, it's better to let the, the body naturally warm up once you've done the cold. If you're for that contra.
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For the last round.
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For the last round.
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I think one mistake that, that people commonly make is they don't let themselves recover enough between hot sessions. So you know, that's a pretty stressful environment.
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Right.
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And you're sweating, blah, blah. And you know, I, I think cooling off for like an equal amount of time that you spent in the, in the hot, I think is probably a good idea and not don't just jump in the cold plunge and then go back in the sauna because you haven't really cooled off yet. Your skin is cold. Your skin is going hot to cold, but your core is not. And so you're still building up heat inside your body. And as you're, as the cold constricts your circulation, right, all the blood goes to your core. You're conserving heat inside you. So you have to like let that relax and let yourself radiate off that, that, that heat that you, that you absorbed in the sauna. So recover for enough time I think is key.
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A
That's sound advice. I buy that. In terms of the cold plunge, you're
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B
not a fan context dependent. But yeah, I wrote the case against cold plunging. So the science of cold exposure and cold water immersion is really not as, as, as robust as the science around heat. By a long shot. A lot of the studies are, they tend to be small, they tend to be biased and there aren't the big long term observational studies of people intentionally dunking themselves in cold water. In fact, most of the cold water literature is about dying from hypothermia. Right. Or having a heart attack or whatever. It's, there's a risk and there's a risk to heat as well. But I think perhaps probably the biggest misconception, it's eroding, it's fading away now. But is this idea that, that it's a good thing to do after a workout or after a Strength workout in particular. And you know, it's understandable because, you know, activating your muscles and running or lifting weights, you generate a tremendous amount of heat in your body and you want to cool off. Right? That's, that's natural. But numerous studies have found that, that immersing yourself in cold water immediately after a workout kind of blunts the muscle benefits of that workout. It stops the kind of the muscle protein synthesis. They did a crazy experiment where they had people do like a leg workout, like a, you know, intense leg, leg workout. I think it might have been cycling at high resistance anyway, leg resistance training. And then they stuck them in individual like leg boots. And one was full of hot water and one was full of cold water. And then they had them drink a special drink that tracked muscle protein synthesis and found that the leg in the warm water had more muscle growth potentially, and the leg in cold water did not.
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100, 100%, yes. If I ever. I agree, like, that's a fact. If you're going to do cold, do it before you work out on after if you're lifting.
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B
If I lived in Miami, I would have a cold plunge outside on my deck and I'd get in it every day though, just for that temperature regulation. And in fact, my sauna place here in Salt Lake has an awesome cold plunge. And I go there in the summer just to, just to dump, dump the heat and, and, and feel cool. It feels good to feel, you know, temperature regulated.
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Yeah, I go twice a week now and I'll do like three or four minutes and I'll do it on the weekends and I just go first thing in the morning after I've had coffee. And it's just a nice way to like, kind of clear my head, reset. I, I watch my heart rate. So like I jump in, heart rate spikes, I'll try to get it below 60, then I'll like, kind of ease and then I get out and. But I don't know if it's been meaningful for me in terms of any metric improvement. Whereas I swear by my cold mattress, if I'm not on my cold mattress, it's my HRV drops and my resting heart rate increases and I don't sleep as well. Like different ballgame and we can talk
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B
about temperature and sleeping as well. So it's a little bit tricky. You know, we think that there are potentially brain benefits to brief cold water immersion, you know, but all those markers are measured in the blood, but not in the brain because you have to kill the person to do that. So some Studies you can't do. But another point I'd like to make, I mean, I feel like a lot of cold plunges are like overly cold. They're like aggressively performatively cold. And there's, you know, based on the experts I talk to, it seems like the physiological benefits of that cold water immersion are really in, in the kind of around the 50 degree mark.
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A
Yeah, I, I do 49, and it's just because that's what the gym temperature is. And I have no control, but I have no control over it. So it is what it is.
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B
It's probably better than 39. In 39, basically, you get more pain than gain.
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A
Look, in my view, with a lot of practices, it's a fine line between you don't want diminishing returns at a
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B
certain point and there's a certain, as I said, performative aspect to it. And people get competitive and, oh, I'm in the 33 degree cold plunge instead of the, you wuss, you're in the 41 degree cold plunge. And I'm going to be in here for 17 minutes. You know, it just gets, it gets silly.
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A
It reminds me one of my friends here in Miami's Mark Sisson Primal kitchen. He lives on the beach. Different life stage because he's in his early 70s and he was, I think it was on the show, he was telling me a story. He was in the plunge and Mark is in ridiculous shape and he's in the plunge. And he said some, some guy got in there with him and, you know, he started competing with Mark and makes a point of saying, like, you know, how long were you in here, Mark? And Mark's like, you know, three minutes, whatever. He said, well, I got seven minutes. Mark was like, what did that get you? Like, dude, you're like, you got to get in shape and work out, but like, who care? Like you trying to kill yourself. Like, it doesn't look like you've done this before.
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B
Yeah, well, I don't know. Maybe it's the clarity that comes from that life stage. But like, I feel like he's one of the more common sense people out there in this world. So I quite like him.
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I have a lot of respect for Mark in that I find him to be very ethical. I find him to. He's his own man, he has his opinion, he beats to his own drum, and he's not here to please anyone in a very positive way. I don't think he's looking for controversy. Just here's how I see it.
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B
I'm, you know, People are going to argue to the death about cold plunging and other things. And, you know, I mean, if it works for you, that's great. You know, we. We just don't really know what it's doing for you beyond very sort of broad brush kind of ideas. And this idea that it, it. I mean, it does. I feel charged up after a cold plunge. But, you know, if I'm having a kind of a crappy day and I'm stressed out and like, you know, angsty, it's not the thing to do for me, you know, I'd rather sit in the sauna than I'd go out. Like the other day I sat in the sauna, went out, and it was snowing. I just sat in a folding chair out in the side yard of this place and got snowed on and it was terrific. I just felt so good.
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A
It's funny you say that. My wife will often hit the sauna in the earth, like in the early evening after dinner before we get our kids ready for bed. If she's having like a stressful day, it's her reset. She loves it. Whereas that'd be the last thing I would think to do. I would not go to a. Sorry, I would. Last thing I would think to do would be go to a cold plunge. If I were having that sort of. I wouldn't do it. That to me, that's like a morning, like, let's go energize, like clarity. Not like trying to wind down.
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B
And it's also good to do with a friend, you know, like a. It's a bonding thing, you know.
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A
So I can't help but think of the Finns and it was just embedded in culture and in your view, A lot of the studies there, I. I think of the social benefits, the connection. It's ingrated in the culture. It's not just being in a sauna with your family or friends and having conversation seems to me like it's a hell of a lot better than just being in there by yourself. Yeah.
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B
And counting the minutes and adding up your, you know, your heartbeats and your heat shock proteins by yourself. Yeah, no, it's, it's. It's a. And, yeah, it's. It's a social ritual. And it's interesting. In this journey, I kind of started out from the standpoint of like sitting in the sauna by myself to, you know, I. Thinking it would do something for my blood pressure. Right. Which it does. And then I kind of. I kind of went from that kind of mechanistic perspective all the way over to this kind of social, more socialized kind of idea of. It's more about like I made friends through all these at the various sauna, you know, stops on my journey. And not just sauna, but other, other places. And, and I don't know, the, the heat seems to break down some walls that we have. And you know, I mean, you don't always want to be chit chatting in the sauna. Sometimes you want to be in there thinking about stuff. But yeah, I mean there's a definite like social aspect to it that, that's kind of taking off in some places. Like New York, for example.
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A
Yeah, he, he's an old friend. Like, what's cool, what they're doing with the culture of bathing, like, and the sauna, the giant sauna in the middle of a storm.
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B
Yeah, I was there. I went there a couple weeks ago.
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A
Yeah, so you know Bill, Bill, the High Line guy.
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B
Oh, Robbie.
- [33:48]
A
Yes, yes. Yeah. So. Yes. Yeah, yeah, yeah, yeah, yeah, yeah, yeah, yeah.
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B
He was the, the maestro of the culture of bathing. But that was a really cool event with I think there's about a dozen of these little saunas, each one sort of architecturally designed and unique and like, you know, spectacular. Just right down there under the Williamsburg Bridge. And it had just snowed and there was another blizzard actually last week. It was interesting. It was cool.
- [34:21]
A
Yeah, I know Robert Hammett, Bobby, from the high back when he created the High Line from New York, he had a vision for this. It looks super cool. If I were in New York, I'd be there. You mentioned blood pressure. And in a world where many doctors just can't agree on anything, it seems like every cardiologist agrees that sauna is positive for heart health.
- [34:45]
B
Yeah, they used to think it was bad and could cause a heart attack, but then they found that the opposite was true. And one of the most consistent benefits is this reduction in blood pressure. And they're still kind of figuring out what causes it, but it's a fairly consistent effect.
- [35:04]
A
So in terms of the science you're, you're researching this book, what stood out, where it's popped off the page, you said, wow, this is interesting. I didn't expect this, expect to see this.
- [35:15]
B
Well, just from, just from the get go, you know, we're kind of told that heat is dangerous always and will kill us. And while that's true in certain contexts, there's also a flip side to that equation, which is that heat can be healing. But I think the biggest. And so to me is not a Heat guy. Originally, that was a surprise, but the biggest surprise was finding, you know, as I kind of went down these wormholes, finding that there's pretty like, solid evidence for a mental health benefit to targeted heat exposure. And originally, like, I just, I stumbled on this crazy study. I was. I did hot yoga, went, tried out hot yoga, and I stumbled across a study that found that people who went to hot yoga for eight weeks had their depression symptoms basically chopped in half or chopped in by a third, which is a pretty big effect. And it turns out there's all this research about basically whole body hyperthermia, which is a fancy way of saying heating somebody up till they have the equivalent of a light fever, and that that appears to have an effect on symptoms of severe depression.
- [36:37]
A
Fascinating. Have they ever done an mri, I guess would be kind of impossible to do. I'm thinking out loud, like an MRI of someone's brain while they're in a sauna.
- [36:50]
B
Oh, God. Can you imagine a heat, a heated mri? I mean, so that's, it's an interesting. There's. There's a lot of stuff that we can't possibly know. Right. But what they have found through animal experiments is that. So in, in these, there was this old study where they, they heated up these rats to like the same level, like a fever level. And then they looked at their brains and they found that a certain brain region started cranking out serotonin at this high temperature. And so one possible explanation for this benefit of whole body hyperthermia, this antidepressive effect that's been seen is that. That it's like doing the same thing as like an SSRI drug.
- [37:40]
A
Again, we moved from New York to Miami. So I buy that heat and sunlight are game changers for mood.
- [37:49]
B
Definitely. And, you know, if you think about going back to the origins of sauna or where sauna took hold and has remained culturally. So Finland, Russia, you know, Baltic countries, it's frigging dark there. Like the sun. Like in Helsinki, the sun is up. It, you know, Christmas time, it's up for like six hours a day, and it's, it's rising and then it's setting. Boom. And it's dark. It's a, It's a tough environment. Right. And you know, my unscientific theory is that going into these hot spaces is somehow kind of a, A salve for that or like a substitute, potentially.
- [38:32]
A
Yeah, 100%. I think if you live in a colder climate, this is more of a must have in your protocol. Whereas if you live somewhere that's Very hot. You could probably experience some benefits just being out and about and working hard during the day and sweating.
- [38:49]
B
Well, if you're in a hot place, a sauna can help adapt you to your local climate, essentially.
- [38:55]
A
So if I'm listening and I'm new to this, what advice do you have to start in terms of like, what's a smart safe protocol? Frequency, duration, temperature. Do you have a view for someone who's a. Okay, I'm sold. Bill.
- [39:09]
B
Yeah, yeah. So, you know, if you're relatively healthy and relatively fit, you probably have some built in heat tolerance. But, you know, you don't have to go in for like 20 minutes at 200 degrees right off the right, off the right off right from the gun.
- [39:28]
A
Right.
- [39:29]
B
Start with less than that. Right. And, and listen to yourself, listen to your body. You know, I try to go like to the point where I'm thinking about getting out and then I go a little bit farther, try to go a little bit farther than that, depending. So when I started going to sauna in my gym, you know, the typical terrible gym sauna, it wasn't all that hot, but I'd go in for like five minutes, I'd go in for eight minutes, then maybe 10. But it was, it was about like how I felt. So I'd go in for. Until I started thinking about getting out and then trying, trying to go a little bit beyond that. And that's for, that's for finish style sauna. You know, infrared saunas are less hot. Right. So people sometimes are tempted to stay in there a bit longer.
- [40:22]
A
Yeah. Look at sage advice. I think something that if it's helpful for the audience. However, whatever I try, that's new. I kind of have like a 20% incremental roll. So like I'll start slow, even if it's like something kind of benign, like, okay, I'm rowing for the first time or, oh, you know, go for five minutes and then the next time maybe I'll go like seven, six minutes or seven minutes. Like I'll incrementally push versus like, oh, I'm all in. Put me in for 220. At 20. Let's see how hot we can take this sucker.
- [40:55]
B
Yeah. And some people are like that, right? They go full extreme all the way. You know, the sauna has a door for a reason. It's so you can get out, you're not trapped in there. And I will say so. For the outdoor heat training aspect of it, the heat adaptation training that I did, I mean, I used a little this kind of cool little device. He it was like a core temperature sensor. It's called the core. And that actually tracked my body temperature as it as I would, like, ride my bike, you know, up the nearest mountain pass here in here in Utah. And so I could watch, I could see, like, even though I be feeling like, oh, man, it's really hot out, I look and see that my body temp was like 100 degrees, so I'm fine. So that was interesting. That made me feel safe.
- [41:52]
A
Yeah, yeah, yeah. I know it's an important point. I'm curious, what was your biggest takeaway from writing this book? What do you want? The message I'll plug the book is hotwired. You are a incredible writer. It's a great blend of hard science and storytelling. You are one of the best. Everyone should buy it. But what do you want the takeaway for the audience to be in addition to obviously buying the book?
- [42:17]
B
You know, I think there's value in leaning into discomfort and leaning into the thing that you think you don't like. And for me, that was heat, but it's also extreme cold. You know, I wrote a cheeky chapter called the Case Against Cold Plunging. But, you know, I'll be honest, I find value in it. And, you know, I, I feel on some level it, it's good for me to do a hard thing. So I think that is, is the biggest takeaway. And it doesn't have to be, you know, sauna's super trendy right now. It could be the hot tub. You know, it's whatever, it's what you like.
- [42:53]
A
You know, I think that's just such a tremendous statement for life. Leaning into discomfort. I, I think we've been so, you know, accustomed to comfort and pleasure, and everyone wants that, and I get it, it too. But the ability to step into anxiety or discomfort or stress and fully own it just sets you up to be in such a better position for life.
- [43:25]
B
Yeah. As opposed to flattening it. Right. So if you're at a flat, constant temperature level, I, I, I think that's not that great for us. Like, I think we're meant to, to be able to, to handle fluctuation in our lives.
- [43:42]
A
Yeah. And a great way to prep. I, look, I'm a huge believer. I mean, like, physical prep and mental prep go hand in hand. So, like, if you want to be stronger mentally, like, physically, that is. It's a great lever to test yourself.
- [43:55]
B
Yeah, absolutely. Absolutely. I mean, you know, there's a reason Olympic marathon runners, you know, finish up sometimes in a sauna. You know, it sounds. It sounds kind of uncomfortable, right? But. They keep that benefit rolling.
- [44:16]
A
Yes. Well, Bill, thank you so much. Book is incredible. Surely another bestseller. Thank you so much.
- [44:25]
B
Thanks, Jason. Great to talk with you, man.