What the world's leading researchers think about saunas

Saunas have gone from a Scandinavian tradition to a global wellness phenomenon. But how long should a person endure heat? Do saunas actually work? And if so, what are their benefits? NPR health reporter Will Stone goes as deep as the science will let him to explore the sauna hype waves and find out what happens to our bodies when we step in them. Interested in more about thermal physiology? Email us your question at [email protected] mailto:[email protected]. Support public media with NPR+ and enjoy perks for over 25 podcasts like this one. This show’s perks include sponsor-free listening. Learn more at plus.npr.org http://plus.npr.org. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:18Speaker 00

  You're listening to Short Wave from NPR.

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  Take a deep breath, relax, because we're going to the sauna.

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  With our very own Will Stone.

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  We are toasty inside a wooden sauna, floating on a dock in the harbor of Oslo.

• 0:46Speaker 01

  I didn't actually get to go to the sauna, but Will did, in Norway.

• 0:51Speaker 02

  The steam collecting and then pushing the hot air to the top. And maybe a little bit of essential oils are wafting in. And there's kind of the creak of the stove as the hot rocks collect heat. And then the whoosh of steam as you throw water on top of it.

• 1:15Speaker 02

  People have been using heat for physical and mental well-being since ancient times. You know, we have steam baths, we have saunas, we have geothermal hot tubs. These days, sauna is making a big comeback. People are going to these social sauna meetups, both in Europe and the U.S. And the practice is also being promoted widely in the wellness and longevity movement. If you look at Instagram, it's rife with claims that sauna can be a kind of miracle detox for all kinds of health issues.

• 1:53Speaker 01

  I've definitely seen those reels, but what do we know about the actual health benefits?

• 1:58Speaker 02

  There's not a ton of scientific evidence to match the hype. The research is surprisingly new.

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  But scientists are beginning to identify some very specific benefits and effects on the body.

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  Today on the show, NPR health reporter Will Stone takes us inside a meeting of the world's leading heat researchers in Norway, trying to suss out fact from hype and the ways that heat might really benefit our bodies. I'm Regina Barber, and you're listening to Short Wave, the science podcast from NPR.

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  Will, I've been hearing so much about saunas and their health benefits lately. What kind of sauna experiences are we talking about? Like, what are the scientists researching?

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  Yeah, so we have the traditional Finnish sauna with the heated stones, and you throw some water on there.

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  Yeah.

• 4:12Speaker 02

  And you should say sauna if you want to make the Finnish folks happy, not sauna, like we do in America.

• 4:18Speaker 01

  Yeah.

• 4:18Speaker 02

  But there are other ways of using heat. There are infrared saunas. There's also just hot water immersion, lots of different forms of heat therapy, which is the kind of broader bucket here we're talking about.

• 4:31Speaker 01

  Okay.

• 4:32Speaker 02

  And so this was the first symposium ever put on about heat therapy and health. And I had been invited there by a clinical psychologist at University of California, San Francisco, named Ashley Mason. She studies sleep and mood disorders, and she's become increasingly interested in using heat for depression, mood, and other areas of mental health.

• 4:53Speaker 04

  Heat therapy research is basically an infant. Scientists around the world are getting interested in this and figuring out ways to study heat therapies. But we're all over the place, and we don't have a body that connects us. We need to establish, how do we write about our work? What are the standards? What are the norms?

• 5:11Speaker 02

  And Ashley is working to do this with a nonprofit called the Sauna Research Foundation in this effort to organize their field.

• 5:19Speaker 01

  Yeah, that's really awesome, because I feel like when me and my best friend Melissa, we've gone to the sauna, we love it, it makes us feel good. But I've never felt like there's a lot of clear evidence for like, why it's beneficial, like, no robust studies that have been replicated. Is that right?

• 5:33Speaker 02

  Yeah, and I think you're touching on something that was part of the focus here of this meeting. Ashley even acknowledged this, that there's this kind of whiff of wellness hype that we were alluding to earlier. They're really trying to move from kind of that to really introduce the field as a rigorous field of scientific research. I mean, even though sauna and other forms of heat therapy have been studied on and off for decades, very little of that research comes from the kind of well-controlled human trials you're talking about, Gina. It's often hard to draw firm conclusions from what evidence does exist, because the studies are small, the methods vary a lot, and key measurements are sometimes missing.

• 6:14Speaker 01

  Yeah, this reminds me of psychedelic research we've talked about on the show, where it's really hard to do a blind test, because when you're in the psychedelic group that trips, you know. And this is similar to when you're in a sauna group, I'm assuming, like, you probably know.

• 6:29Speaker 02

  Exactly. I mean, I cover psychedelics, and I hear some similar themes when we talk about the need for these robust trials that can be replicated. I talked to one scientist in the sauna world, who said he had counted over 100 different protocols have been used across studies over the years.

• 6:48Speaker 01

  So, Will, how are they trying to figure this out? Like, the researchers you spoke to in Norway, like Ashley Mason?

• 6:54Speaker 02

  I mean, the first step is just to get on the same page. And they're doing this pretty wonky process of building consensus in medical research. They're trying to pin down definitions, what needs to be measured and reported in each study, how do you define heat therapy? And then a bunch of like, minute details, environmental humidity, how do you measure body temperature? Lots of stuff that probably the average sauna goer doesn't think about.

• 7:21Speaker 01

  I definitely think about humidity and body temperature while I'm in the sauna. Like, I totally do, Will, come on.

• 7:27Speaker 02

  Okay, Gina, well, I doubt you were thinking about, you know, taking the rectal temperature appropriately and when is best to do that?

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  No.

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  But maybe I'm wrong there?

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  No.

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  But that's actually super important. When you try to run these carefully controlled trials, it will matter. How did they measure the body temperature of a participant?

• 7:47Speaker 01

  You're totally right. Okay, so stepping back here, clearly, our understanding of how saunas may help us is evolving, and will hopefully get way better soon. But in the meantime, what do we know about the health benefits of, you know, sauna, based on the evidence that's out there?

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  So to be clear, scientists do have a good understanding of our acute physiological response to heat and how our body tolerates extreme temperatures. I mean, this has been studied by thermal physiologists for a long time. Actually, a fun side note here is that in my reporting, I learned about these British doctors and scientists who conducted these experiments in the late 1700s. They basically converted rooms into kind of super saunas with temperatures, in some cases, well over 200 degrees. And then they wanted to see what happened to the human body because they didn't know, you know, would we cook, basically?

• 8:39Speaker 01

  Oh, my god.

• 8:40Speaker 02

  Put themselves in, you know, different chambers with different temperatures. They even brought a dog or two. Don't worry, a dog was OK. And then they were like, looked at steak and eggs that they had also brought in there. And they noticed that, hey, our bodies did not cook like the food did. And those were actually became some pretty well-known experiments, you know, in the history of, you know, the field of thermal physiology.

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  Why didn't we cook?

• 9:08Speaker 02

  Well, we have circulatory systems and all kinds of mechanisms in our body that help us cool down.

• 9:14Speaker 01

  Yeah.

• 9:14Speaker 02

  And so, you know, this is probably familiar to people who have been in heat. You know, your blood vessels dilate, your heart rate speeds up. Blood is pushed to the skin where it's cooled down as we sweat. There are other things that happen. Our body releases human growth hormones. It activates these heat shock proteins that protect our cells. So the question is, does exposing yourself to extreme temperatures as we do in a sauna on a regular basis provide measurable benefits when you're talking about preventing or treating disease? That's the area that still needs a lot of work.

• 9:50Speaker 01

  OK. So are they getting closer? Like, does it?

• 9:55Speaker 02

  Maybe, probably. You know, the problem, as we've been discussing, is the evidence base. One reason to believe it does do something is that heat works the cardiovascular system in ways that are similar to light physical activity. And studies show it delivers some of the same benefits afterwards. You know, you'll see improvements in blood pressure, arterial stiffness, vascular health, also some changes in metabolism, how the body manages blood sugar, cholesterol. These are some of the observations from the studies that have been done.

• 10:30Speaker 01

  Yeah, I actually just got diagnosed with high cholesterol. So, you know, I love this. Like, maybe this is an excuse to do saunas more, you know, and just like, walk away, do 10 minutes in a sauna.

• 10:41Speaker 02

  Yeah, well, this is actually a big focus of the research. Can we take people with certain diagnosed medical conditions and treat them? And I talked to a researcher in Norway named Ant Sheppard. He's a professor of clinical environmental physiology at the University of Portsmouth in the UK. And his lab is particularly interested in how heat may be able to help people with cardiovascular and metabolic conditions, as well as the elderly.

• 11:07Speaker 05

  Can we take people with disease and use the stimulus as like an exercise mimetic? So can you get some of the same effects you would get with exercise in people with disease who will not or cannot exercise, but who will just sit in a hot tub? And we all know exercise is king, exercise is medicine. But for those that can't, can we get some of the same effects? And it looks like we can.

• 11:29Speaker 02

  Now, all of this research is intriguing, but it's still early days. Many of these studies are small, and they're usually more like pilot trials. So another one of the organizers at the symposium was a researcher at the Montreal Heart Institute named Eric Lee. And he has run one of the only randomized controlled trials on sauna bathing that showed that adding it to an exercise regime gave extra benefits for people at risk of cardiovascular disease.

• 11:55Speaker 01

  Yeah, a lot of the popularity around sauna going has to do with how it makes you feel, right? And you come out, you're calm. You usually go with other people. So there's this community aspect. Do the researchers talk about that at all?

• 12:09Speaker 02

  Definitely. Mental health is one area that you're hearing a lot about. And there are several trials going on right now to understand the benefits you're talking about. When I was in Oslo, I visited one of these floating sauna villages that had been constructed on the harbor.

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  This is a song. It's a Tartar song.

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  And one of my favorite experiences was being inside this floating sauna where a woman named Hilda Carlson was spreading fragrances and performing a kind of ritual where she even sang folk songs while people relaxed in the steamy heat.

• 12:49Speaker 02

  And I gotta say, it's just such a fun vibe. Everyone is laughing.

• 12:58Speaker 02

  They're socializing. They're jumping into the fjord between their sauna sessions. So it's easy to see why this would be beneficial for mental health and mood. You have social connection, time in nature. A lot of people are talking about how great it is to be away from their phones. So you also have this digital detox as well.

• 13:17Speaker 01

  Yeah, I definitely need that.

• 13:18Speaker 02

  We all do. But what I learned is that there are also some real biological explanations for why sauna or other forms of heat therapy may help people with depression, for example. So, you know, the science here is that when our skin senses heat, those signals travel to a primitive part of the brain that tells our body to cool down. And that process overlaps with a pathway involved in mood and pleasure, which is also implicated in depression.

• 13:45Speaker 01

  Do you have any practical advice for people looking to get into, like, saunaing?

• 13:50Speaker 02

  Yeah, the basics are, you know, like exercise, you start slow and then build up over time. Eric Lee thinks of it this way.

• 13:58Speaker 07

  You've gotten to the point where it's like, oh, you can sit in a sauna for 20 minutes straight, you know, with no water, which I don't encourage.

• 14:09Speaker 07

  But you can go for the sauna for 20 minutes straight. OK, you're good. Most people can't do that.

• 14:15Speaker 02

  You can basically keep a log about how long you spent last week, like you would in the gym. But he made it clear that it's not like your goal needs to be to always do more and more.

• 14:24Speaker 07

  What's your goal? You gotta ultimately ask yourself.

• 14:27Speaker 02

  And one thing where the consensus was clear when I spoke to scientists at this symposium in Norway was that you shouldn't be too serious about this. You know, just enjoy yourself and don't make it one more thing that you try to optimize or improve on.

• 14:44Speaker 01

  Will, thank you so much for this reporting. I'm gonna go get in the sauna now.

• 14:50Speaker 02

  Fun. Well, thanks, Gina. It's always a pleasure to come on the pod.

• 14:55Speaker 01

  This episode was produced by Alana Gordon and Juan Diego Ramirez. It was edited by our showrunner, Rebecca Ramirez, and Will checked the facts. Jimmy Keighley was the audio engineer. I'm Regina Barber. Thank you for listening to Short Wave from NPR.

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