How Heat Transforms Your Body (Heart, Brain, Appetite & More)

What if I told you that sitting in a 180-degree wooden box a few times per week could reduce your risk of heart disease, improve brain function, reduce appetite, and even help you live longer? I know, I know, it sounds like wellness hype, but hear me out because the research says otherwise. In this video, we're going to break down the stunning science of saunas. We're going to talk about compelling human data, get into the nitty-gritty of mechanistic details, and give you some practical takeaways as well in the form of protocols. But first, let me explain the basic types of saunas so you have some bearing. We're going to go over the Finnish dry sauna, steam sauna, and infrared sauna. A traditional Finnish dry sauna is generally heated with a wood-burning stove or electric heater with stones on top. The temperatures are hot, ranging from 70 to 100 degrees Celsius, which is 158 to 212 Fahrenheit, and humidity is typically quite low. These saunas are intense. They're really good for cardiovascular conditioning, as we'll get into in a moment, and they probably have the strongest data overall for outcomes like reduced all-cause mortality, i.e., death. And I'll show you data on that a little bit later. Then there are steam saunas. These are typically cooler, typically 40 to 50 degrees Celsius, which is 104 to 122 Fahrenheit. They're generally closed, often tiled rooms with high humidity, often near 100% humidity. And while overall less intense than the Finnish dry sauna, steam saunas feel great for clearing out congestion and soothing airways, and still impart a decent amount of heat stress. Finally, there are infrared saunas that use lamps to directly heat your body with infrared rays. They operate at lower temperatures, at least compared to the Finnish dry sauna, in the 45 to 60 degrees Celsius range, or 113 to 140 Fahrenheit. They're also typically low humidity. And since the infrared rays penetrate deep tissue, this is great for muscle recovery and reducing inflammation. And the lower temperatures allow for longer sauna sessions. And these saunas have a big advantage of accessibility and are good for home use. Now let's dive deeper into the scientific literature on the health benefits of saunas, starting with heart health and the cardiovascular system. Saunas can improve heart health in part by mimicking cardiovascular exercise, like running on a treadmill, but you don't actually have to run. They increase heart rate and can increase cardiac output by up to 70% and improve blood flow throughout the body. They can also help reduce chronic inflammation, with more frequent sauna use being associated with lower levels of inflammatory markers like C-reactive protein, or CRP for short. Maybe you've heard of that one. And saunas can also increase levels of anti-inflammatory molecules like IL-10. And saunas can help improve the function of the endothelial cells lining blood vessels, which is really important for heart health. But I'm getting ahead of myself, I promise. We're going to get deeper into the mechanisms on the back half of this video. You won't be starved for mechanisms. But first, let's look at some really cool human studies to convince you saunas are worth your time. And then we'll get back to being super nerdy. Okay. The notable benefits of saunas for heart health were popularized by a series of several major studies, including one published in JAMA Internal Medicine 2015, where researchers followed a group of 2,315 Finnish men for a median duration of 20.7 years, and they compared the frequency of sudden cardiac death and cardiovascular disease between those who used saunas frequently, 4 to 7 times per week, versus those who use saunas more rarely, about once per week. And they found in this population that those who use saunas 4 to 7 times per week had a 67% reduced relative risk of sudden cardiac death as compared to the low sauna users. 67%! That's pretty incredible. And this was after adjusting for age, body mass index, blood pressure, smoking, alcohol, diabetes, physical activity, and socioeconomic status. Pretty amazing. And similarly, there was a 50% reduction in fatal cardiovascular disease, in the heavy sauna users. Now, as for some more specifics, the average temperature of the Finnish dry sauna used by this population was 174°F with sessions lasting about 14.5 minutes on average. Let's round it to 15. And notably, longer sessions, those lasting more than 19 minutes, elicited an even more robust protective effect, suggesting a clear dose-response relationship. In simpler terms, more might be better in terms of both frequency and duration, at least up to a point. But based on these data, 15 minutes of sauna use 4 times per week would be excellent as a starting point. Now, moving on to the benefits for the brain. First, saunas can increase levels of the brain protective hormone brain-derived neurotrophic factor. One study showed that a heat challenge, in this case 20 minutes of hot water immersion at 42°C, significantly increased BDNF levels, whereas immersion in a control thermoneutral water did not. What does BDNF do? BDNF, brain-derived neurotrophic factor, supports neuroplasticity, the brain's ability to form new connections. It improves memory and learning and may protect against neurodegenerative diseases like Alzheimer's disease and Parkinson's disease. Furthermore, saunas increase levels of something called heat shock proteins. Heat shock proteins help other proteins fold properly, which is absolutely critical in preventing neurodegenerative diseases like Alzheimer's and Parkinson's, both of which are characterized by misfolded proteins, like alpha-synuclein in Parkinson's disease and amyloid and tau in Alzheimer's. The idea is this, that saunas increase levels of these heat shock proteins that prevent misfolding of other proteins, and those heat shock proteins stick around well after you've gotten out of the sauna. So if you sauna routinely, you can effectively keep boosting your heat shock protein levels, potentially keeping your brain healthier as you age. Speaking a bit more to the human data, in one randomized controlled trial comparing heat stress with a 30-minute session at 73°C, which is 163°F, compared to no heat stress in 25 healthy young men and women, the sauna users increased levels of one heat shock protein HSP72 by 48.7%. And other studies have shown that bouts of heat stress can also increase levels of other HSPs by 35 to 50%, and that this adaptation has a lingering effect. In other words, routine sauna use can help keep your heat shock protein levels consistently elevated, which is thought to be neuroprotective. And interestingly, and that was a quick aside, ketones produced by the body on ketogenic diets or with exogenous ketone supplements, and I'll drop a recommendation to my favorite ketone supplement below, anyway, ketones also appear to help with protein misfolding in a complementary manner to potentially prevent Alzheimer's disease. For more on those really interesting data, see this video, which includes input from the first author of a key paper in question. But with that aside, back to saunas. In a prospective study on Finnish sauna users drawing from the same population of 2,315 men discussed earlier, researchers found that routine sauna use at that 4 to 7 times per week dose was associated with a 65% reduced risk of Alzheimer's disease as compared to those who use saunas only once per week. That's really impressive, right? And you can start to see the consistency of the findings across chronic disease states—heart disease, Alzheimer's disease. And we'll get on to more in a moment. And remember, this statistic includes adjustment for BMI, age, smoking, alcohol intake, diabetes status, blood pressure, among other factors. With that said, I still want to caveat, these human studies are associational. This is in part because you can't practically do a 20.7-year-long randomized controlled trial very easily in humans. So they can't prove causality. However, the consistency of the results, the size of the effects, and the biological explanations underlying brain-derived neurotrophic factor, heat shock proteins, the thing we've just talked about, are, I think, collectively compelling. Now, a quick comment on longevity. Typically, better healthspan, so lower cardiovascular disease, lower brain disease, should translate into a longer, healthier life at a population level. And we do in fact see this. There's about a 40% reduced risk of all-cause mortality in those who use saunas at that 4 to 7 times per week dose as compared to the low sauna users. Pretty cool, right? Yeah, heat stress could help you live longer. Now, a word on why some people feel so incredible after getting out of the sauna. Me, I feel freaking fantastic. Here's a really cool mechanism. Consider this: beta-endorphins in your brain, they contribute to that sense of euphoria, kind of like a runner's high during exercise. They work by binding receptors called mu opioid receptors. And saunas can increase beta-endorphins, so creating this sense of high. But that's not all. Saunas can also increase another brain chemical called dynorphin. Now, dynorphin is kind of the flip side of the coin to beta-endorphins. Dynorphin creates a sense of discomfort. And certainly, an intense sauna session can and probably should be discomforting. Dynorphin likely contributes to this feeling by binding to not mu but kappa opioid receptors. But here is the fascinating part. This dynorphin kappa receptor interaction may loop back to make the mu opioid receptors more sensitive to beta endorphins. So by analogy, if that didn't make sense, maybe you've heard of insulin sensitivity, how well your body listens to the hormone insulin. Well, imagine dynorphin is increasing your endorphin sensitivity, which may further enhance that post-sauna feeling of euphoria. And a giddy high. Pretty cool, right? Well, I guess technically hot, but still cool. And to give credit where it's due, I just want to say I first became aware of this mind-boggling mechanism when reading a review article by Dr. Rhonda Patrick, who is arguably the number one among public science communicators for speaking consistently about the benefits of saunas. I'll link to more resources below, including that review article. In the video notes. So definitely check out the video notes, there's going to be a lot more there. Finally, before we get on to protocols, here's one last fact about saunas that I found fascinating. They can help reduce appetite and food intake. It's been observed that heat exposure reduces food intake both in humans, even in early randomized controlled human trials, and in animals, which leads some to suggest that heat stress may be a weight control tool. And new science is beginning to unpack how heat may suppress appetite. So get ready, I want to warn you, this is going to be a steam burst of jargon, then I'm going to simplify for you. A recent paper published in Nature just last year found that heat activates specialized cells that line the fluid-filled spaces in the brain. These cells are called tanocytes. These tanocytes are optimally placed to communicate external signals from the outside world to regions of the brain, in particular the brain's hypothalamus, that control things like metabolism and food intake. And this new research found that heat stress in a mouse model at 40°C for 1 hour increased activity in a temperature-sensing region of the brain called the pontine parabrachial nucleus, which signaled to tanocytes, causing them to produce a a brain chemical, vegFA, which in turn signaled to the hypothalamus to change the activity of dopamine and AGRP neurons and leads to reduced food intake. I know that was a total word salad, probably, to many of you. But basically, the researchers discovered a mechanism that appears causal and necessary for the effects of heat on reducing food intake, at least in animal models, but this aligns with data in humans. That heat can reduce food intake. Pretty cool, right? Now, after that word salad, I'm sure you're really hungry to know about the best protocols for sauna use. Well, the number one thing I can tell you is consistency is key. If you can, use the sauna 4 to 7 times per week for 15 to 30 minutes per session. That will be awesome, and you'll reap huge rewards. Of course, be safe, but do push yourself. As with exercise, benefits from sauna derive in part from you pushing your body to its limits, forcing it to adapt. The nerdy term for this is hormesis. And as you build up a tolerance, you'll be able to do more and more. That is good. Just stay hydrated and try to push yourself like you're training your muscles to lift heavier weights and more reps, except here, Your variables aren't heavier weights and more reps, they're temperature and time in the sauna. And I'll also note, this should be you time. You should enjoy it. I know many of us have super busy lives, so it's fine to double task. For example, I— and bear in mind I'm quite weird— I love to cap off my workouts with 100 to 200 hot box push-ups while listening to podcasts. For me, it's a way to maximize intensity because push-ups at 200°F they're no joke. And I'm kind of an intense person if you haven't noticed. I've also heard, as another example, that Dr. Rhonda Patrick, who talks all the time about saunas, as I already mentioned, likes to read scientific papers in the saunas. She can do this, spend enough time in the saunas to actually read papers, because she's built up a tolerance. And she also reports that her memory and learning seem to be accentuated, improved by the sauna. So this practice might help boost her retention to scientific information. So maybe you should put on this video again while you're sitting in the sauna. So, in conclusion, if you're looking for a way to boost heart health, sharpen your brain, reduce inflammation, and maybe even feel euphoric—try it out, I think it's quite a potent sensation—consider making sauna sessions part of your routine. Finally, if you learned something new, or just enjoy watching a young scientist subtly reveal that his spirit animal is a rotisserie chicken, hit that subscribe button. Thank you so much, stay curious, stay sweaty, and I'll see you in the hotbox.