What's the Deal with Cold Plunges and Saunas?

Perry: [00:00:02] Emily, I have an audio challenge for you. Are you ready? I'm ready. Okay, I want you to listen to this following clip. And your job is just to tell me what's going on here.

Influencer: [00:00:17] I don't know if I can do this. Remember? It's a countdown. Just say. Countdown. Ahhh!

Emily: [00:00:30] So, Perry, I think this is going to reveal too much about my internet consumption, but I think that I have seen the video associated with that audio on TikTok.

Perry: [00:00:40] Wow.

Emily: [00:00:40] And that person is cold plunging in an icy lake.

Perry: [00:00:46] I believe I have once again underestimated your ability to understand the internet zeitgeist. Emily. Um, you're correct. That is not a lake. It is a tub of some kind that is filled with icy water. But I will say that being new to exploring the world of social media, wellness influencers and looking at a bunch of cold plunge videos, this is what I took home was this seems terrible. I agree. No one enjoys this.

Emily: [00:01:18] I agree, I think that if there are any benefits, it is that you are just so happy to be out and not dead that everything about your life after that seems better because you are not in an ice pit.

Perry: [00:01:31] There is no joy without sadness. Perhaps that is the philosophy of cold plunges. This week we're going to explore extreme cold temperatures on your body, as well as hot temperatures on your body in the form of saunas, two ends of a bipolar system of stressing the body with temperature. We'll figure out if the data supports whether these things are beneficial or not. Should we dive in?

Emily: [00:01:52] We should dive in. I'm Emily Oster, I'm an economist and a data expert.

Perry: [00:01:59] And I'm Perry Wilson. I'm a medical doctor.

Emily: [00:02:02] It's Thursday, February 26th, 2026. And this is Wellness, Actually.

Perry: [00:02:07] Because you're getting a staggering amount of health and wellness information nowadays from every source imaginable. And some of it is awesome.

Emily: [00:02:16] And some of it is, well, actually, bullsh-t. Fortunately, we're both people who know how to read studies, how to parse the data, and can tell you what's worth thinking about and what you can safely ignore.

Perry: [00:02:29] But before we dig in a note that this podcast is for educational purposes and should not be construed as medical advice. We don't know your unique situation, so talk to your doctor for personal health decisions.

Emily: [00:02:40] This week we're asking what's the deal with cold plunges and saunas? And then we'll get to your question of the week. But first let's do the health news roundup after the break.

Perry: [00:03:01] Now on to the Health News of the week. Emily, I am looking at cdc.gov. Measles numbers, um, through last week through February 13th. There have been 910 total cases to date this year. 2026 the United States. Uh, there were 2280 in all of 2025. Last year, if you do the math, uh, we're at about three times higher than 2025, which was a particularly bad year to begin with. Uh, there are measles outbreaks in the majority of states. What are you taking home from the new data?

Emily: [00:03:40] The measles data is is really pretty scary. I mean, I think it's worth saying you highlighted that we are seeing more cases than 2025. Let me give you a what I think is a sharper fact, which is that in a single week in January of this year, we had more measles cases than all but a small handful of years over the past three decades. And so really, this is an unprecedented set of outbreaks. We are likely to continue seeing them. So those numbers that you gave go through the sort of second week of February already, since those there have been announcements of a reasonably large outbreak at a college in Florida, announcements of a beginnings of an outbreak in Salt Lake City. So we're going to start seeing more of this around. And it is happening for a very basic reason, which is that measles is super contagious. It can live for a very long time on surfaces. So one number that's probably useful to put out there is when we talk about diseases and their contagiousness, we talk about a number called r-naught, which is how many people someone is expected to infect. If we kind of had a totally disease naive population. And so for measles, that number is estimated to be sort of somewhere in the range of like 12 to 18. So every case of measles infects another 12 to 18 people. By contrast, for a number like flu, it's a little bit above one maybe maybe 1 to 2. And so this is just so contagious. And when it faces a population with lower vaccination rates, which is what we have, a lot of people are going to get measles. And that's just kind of what's going to happen. That's it.

Perry: [00:05:18] Yeah. There's really no reason to get measles. Um, that's that's the thing that I keep coming back to. I see these stories of kids who've been hospitalized. A couple of children died last year. You know, you can read the statements from families, by and large, who, even in the face of this, will often say things like, you know, I don't regret the choices I made. And I understand there's some self-defense mechanisms at play here, but just to say it out loud, like measles is one of those things that we have defeated, by and large, like we won this particular battle. There's no reason to keep fighting it.

Emily: [00:05:51] Yeah. I mean, I think it's just it's just very sad to say, you know, children will die this year. Measles. The measles mortality rate. Something like 1 in 1000. So there will be kids this year who will die of measles, who could have not died. And I think when you put it like that, it's just that's just really sad. That's all. Yeah, it's really sad. Okay. Moving on, uh, to some appointment news in the federal government. So Jay Bhattacharya, former professor at Stanford, economist and doctor. So he's like both of us.

Perry: [00:06:26] Uh, the perfect mix of you and I.

Emily: [00:06:29] I'm sure he's in charge of the NIH and has now been named as the acting director of the CDC. Uh, Jay is known for many things, but one of them is during Covid. He was one of the authors of the Great Barrington Declaration, which in the fall of 2020 argued for a more focused approach to Covid, which would have protected the elderly but allowed Covid to spread more widely among healthy people. Got a lot of attention and hate for this at the time. He has now been put in charge of not one, but two major parts of the federal disease infrastructure. Your thoughts.

Perry: [00:07:04] Including the part of the federal disease infrastructure that's responsible for containing outbreaks of disease, just to to say it. So let me let me take issue with one thing you said about the Great Barrington Declaration, which is you said it would have protected older people and let the virus sort of spread throughout, you know, less vulnerable populations. That was the pitch. I think the reality is protecting older people. You can't just say like, oh, we will protect people. You have to actually demonstrate it. And as all outbreaks have shown us, it's really hard to do that. Like, do you try to isolate people? Are you sliding food under the doors of older people's homes and so on and so forth? Um, so, you know, I don't think the Great Barrington Declaration was well thought out. It was primarily ideological. And that seems to be the way this administration works is that they pick an ideology that they favor, and they put people in charge of the scientific apparatuses who believe in that ideology, as opposed to people that are behaving like scientists, which is to look at data and to derive conclusions from the observable data.

Emily: [00:08:08] Let me say one thing here. Where so I, I know Jay pretty well, and he is a very smart guy who, you know, getting back to our measles discussion, I think does fundamentally believe in routine childhood vaccinations. And if you asked him, would say people should get the measles vaccine. So I have what is presumably a somewhat naive hope. But I do think that relative to some of the vaccine rhetoric that we're seeing coming out of the administration, this is a more evidence based voice on some of these pieces. I'm a little worried that the job of being both in charge of the NIH and in charge of the CDC is just too much job for a single person, even an economist.

Perry: [00:08:54] It is. It is a big job. I hope you're right. I'm not going to hold my breath. I think what I've seen from even very smart people in this administration, and I know some of them too, although I don't know. Jay is a tendency to cave to the political winds as opposed to the scientific evidence. But we'll see.

Emily: [00:09:13] I guess we'll find out.

Perry: [00:09:15] Speaking of terrible pandemics that may imminently sweep the nation, I'm wondering if you saw this article about a 5000 year old bacteria that was discovered in an ice cave in Romania that just so happens to be resistant to, like, all modern antibiotics. So, like I've read this book, I'm pretty sure I think we all turn into zombies in the next 60 to 90 days.

Emily: [00:09:41] I think Michael Crichton wrote like nine versions of this book.

Perry: [00:09:44] Yeah, yeah. All great.

Emily: [00:09:46] This is published in in a frontiers journal. So the discussion says this bacteria SC 65.3 sounds like a peptide represents an ancient ice adapted psychrobacter with a dual profile of multidrug resistance and antimicrobial activity, highlighting ice caves as underexplored reservoirs of ancient resistomes and bioactive traits. I felt like when I read that I was like, man, let's maybe not explore more. I feel there may be over explored more or less. Leave the ice caves where they are. So I mean, realistically, should we be concerned about ancient bacterias coming out of the explored ice caves?

Perry: [00:10:26] I think there is a theoretical concern. The authors actually in that paper, they're quite positive. They're like, oh, we can learn new ways that bacteria develop antibiotic resistance that we hadn't thought of. And thus we can create new antibiotics. So there's always there's always value here. You do have to be careful. I mean, the truth is that there's permafrost all over the Earth. Um, that contains ancient organisms, some of which are capable of infecting humans and some of which haven't infected humans for thousands of years, but nevertheless can persist under the ice. And some of that ice is receding right as the as the climate warms. And so, you know, there are a lot of ways that new pathogens can get into the human population. The most common is we invade the territory of some animal that we haven't had a lot of interaction with, and some virus in that animal or bacteria in that animal hops into humans. That's probably what happened with all the SARS viruses like Covid. Um, in any number of others, as well as several Michael Crichton books. But, you know, ice, uh, ice melting is another potential vector here. It's definitely something that we should be aware of, but probably not freak out about.

Emily: [00:11:33] Okay, I think that's it for the health news. I feel like next week we need to go have more Olympics because I miss the discussion of condoms. I would rather discuss Olympic condoms.

Perry: [00:11:42] We can discuss. We should. We can have a running like. How many condoms have they used now? And like, just have that number exponentially rising I assume, as we get closer to the end.

Emily: [00:11:51] So with that first a break and when we come back, cold plunges and saunas.

Perry: [00:12:02] All right, we are back. And it's time to talk about your hot and your cold. You know, Katy Perry is on my mind this week because we're talking about cold plunges and saunas. Um, both of these things are all over the wellness space. You've got promoters on all sides. As I've explored this, I've seen people making claims from the idea that they're a nice way to relax after a workout to they will improve diabetes control. I mean, it is all over the map. Lots to dig into here. But Emily, before we get started, I feel like we need to just kind of define our terms. Can you walk us through, Like what is a cold plunge? What is a sauna?

Emily: [00:12:45] All right. So generally, and I will say, part of what's hard about this space is that this is not well defined. Because really we're talking about a lot of things, many of which are done in the wellness space, which is an unregulated, vague space. But when people talk about cold plunges, they are generally referring to being in a some body of water largely submerged for an amount of time that varies from, like, I jumped in the water and I got immediately out to sitting for, you know, 5 or 10 minutes. The water is generally extremely cold. Uh, typically ice icy. Often people will do this in the like low budget version of this is I've got like a giant backyard, like metal tank. And then my Instagram video will have me walking out and, like, cutting a hole in the ice on the top of my tank and then getting into it often with my husband or wife so we can have a romantic popsicle.

Perry: [00:13:47] Worst date night ever.

Emily: [00:13:48] Worst date ever. But anyway, so that's so. It's very, very cold. Of course, they also make like more expensive tubs that will regulate this temperature for you. It's very cold, relatively short period of time. Then there's a sort of hot side of this, um, which actually is quite a bit more varied. So, uh, you can be hot in a sauna, or you can be hot in a hot tub, or actually in sports, you can be hot in, like exercising in, like a winter coat.

Perry: [00:14:16] Oh, yeah. And like hot yoga, right? I mean, I guess you can be. That's a sauna, right? Yeah.

Emily: [00:14:20] Hot yoga is a sauna. Um, although it's not like a dry sauna. And in fact, if you get into, like, the Finns, a lot of the data on sauna is from people in Finland. And the Finns have, like, a lot of really specific things about their saunas, like different kinds of saunas. The saunas are the rocks, saunas without the rocks, I don't know. But at any rate, you are quite hot for a period of time, typically a bit longer. So sauna or hot tub exposure is often something like a half an hour, you know, longer in the hot tub than than in the sauna. And the idea is just to raise your to raise your body temperature for some extended period of time. So basically we're talking about being either very cold or very hot. I think it's just worth saying both of these are uncomfortable. So we're talking about not like a relaxing bath with candles. We're talking about like most people do not enjoy being in a hot tub for 30 minutes, especially since in the heat treatments usually you have to have your arms in, so you're just really hot. Like it's just like really hot and uncomfortable or really cold and uncomfortable. But but if.

Perry: [00:15:26] If I had a nice Finnish sauna in my office right here and a giant bathtub full of ice, and you asked me which one I'd rather spend 15 minutes in. I'm taking the sauna every day of the week. Just going to say it.

Emily: [00:15:38] I think that's right. I hate being both hot and cold. I just, I like to be one intermediate temperature. That's perfect. I find both of these ideas like, almost unbearable. But I do think I would also choose hot. Although the last time I was in a sauna, I literally made it 45 seconds before I was like, oh my God, I have to leave. I'm going to die.

Perry: [00:15:58] Okay, oh, you're okay. So you're you really like your, uh, your homeothermy or whatever?

Emily: [00:16:03] Yeah, sure.

Perry: [00:16:04] Regular person. Somewhere. Somewhere in the middle. But if there are real health benefits, right? Like, maybe it's worth it. Maybe what I think we need to figure out.

Emily: [00:16:12] All right, let's. Before we figure out the health benefits, though, let's talk a little bit about like why these might matter. Like what's the physiology. So you're the doctor. What is the physiology of these kinds of exposures to extreme temperatures.

Perry: [00:16:26] Sure. And let me say like a little bit of philosophy of wellness here, where I think this might be a recurring theme in our podcast, which is that in medical science we start with this concept called biologic plausibility, which is is it possible that this thing works or not? Does it work just like, does it make sense? You know, if someone came and said eating red jelly beans cures cancer, I would say there's no biologically plausible way that that is true. It's not really worth your time. Where I think wellness gets it wrong is that they stop there. They say like, oh, it's plausible and therefore it does. And where we need to go is like, okay, maybe it's plausible, but like, does it actually. And there's, there's a wider gap between plausible and reality than people often think. So let's first of all just talk about biological plausibility. The physiology of cold water plunges is pretty interesting. And we have a good amount of data on this, believe it or not, because the military is really interested in what happens to people when they drop into cold water. This is something, I guess, that we do. We probably do it more often than we know that we do. Um, and so the Department of Defense has funded quite a few studies exploring, like, the short term and medium term effects of these cold water plunges. It's not exactly the same as, you know, calmly getting into ice water in your backyard.

Perry: [00:17:48] But there's a very standard physiologic response called the cold shock response, which is well described, which happens in the first 30 to 90s of getting submerged in cold water at about 40 degrees, 45 degrees or less. And it is essentially involuntary. It is characterized by deep and rapid intake of breath. Like a feeling. Yeah, and that's about three liters of air intake. And just to put it in context, breathing kind of normal, like in and out, is maybe a leader in and out of air intake. So you're really this like very deep breath. And this is actually when people fall through the ice or something. This response is what results in a lot of drowning, because if your head's underwater and you do that, you just suck in a ton of water can be very dangerous. You get this dramatic again. First 30 to 90s a dramatic increase in the sympathetic nervous system. This is that fight or flight response which is going to increase your heart rate, your blood pressure spike, your cortisol levels. It increases adrenaline levels by a factor of about five. In these studies, your adrenaline just goes through the roof in those 60 minutes. Interestingly, dopamine levels increase by two and a half fold. So we often think of dopamine as sort of like a feel good chemical. But you've got a lot of a lot of chemistry going on in that first minute in the ice. And it's obviously not entirely pleasant.

Emily: [00:19:14] So what was the pleasant part?

Perry: [00:19:15] The dopamine.

Emily: [00:19:16] The dopamine, the dopamine that's going up. What is the dopamine going up. So your so your body is convinced like don't just die right now. Things could improve in the next 90s.

Perry: [00:19:27] Yes we call it hope-amine. It's like uh, I'll give you a hug and then slap you in the face as hard as I can. I don't know. It's not great. I just want to give the good and the bad. Okay. Vasoconstriction. So when you get cold, your superficial blood vessels constrict to reduce heat loss to the environment. So blood gets shunted away from your skin and potentially your muscles. I think we need to get into this a little bit to your central organs, which are the things that really need to keep you alive, like your heart and your brain and your kidneys to some extent. Um, it also makes you have to pee. And as a kidney doctor, we see this not infrequently in the hospital. So after someone has a traumatic brain injury or a stroke, if we catch them in time and they're in very severe cases, we will induce hypothermia. There is some data there for brain injuries. That recovery is better with hypothermia. And we do see that as you reduce their body temperature, the urine output goes up because blood is getting shunted away from the periphery and into the kidneys. So if you jump in that cold plunge pool and you have to get right out to pee, that's a great excuse. Um, one last thing on physiology, because this is something that's actually potentially dangerous with cold plunges, and that is the mammalian diving reflex. This is a thing that happens when you submerge your face in cold water. It basically is an evolutionary artifact of our instinct to change our physiology when we're swimming, or especially when we're going deep underwater. What happens in the mammalian diving reflex? Again, only if you put your face in the water is your heart rate goes down. Um, it sort of slows your metabolism. And this is potentially a problem because the cold shock response makes your heart rate go up. The mammalian diving reflex makes your heart rate go down. And there is some evidence that those conflicting signals can precipitate a cardiac arrhythmia. And people have died within the first couple minutes of a cold plunge, potentially through this mechanism.

Emily: [00:21:26] So don't put your face in the water.

Perry: [00:21:27] Don't put your face in the water like I saw a lot of the TikToks. It was like, okay, you're in, like, now go all the way in. Like, probably not, actually, certainly not in the first couple of minutes while you still have the cold shock response going on. Um, so that is the cold side of things.

Emily: [00:21:43] Okay. It sounds terrible. Tell me about being hot.

Perry: [00:21:47] Okay. The warm side I think is a little bit better. So, um, so what happens when you're exposed to heat is that your body does stuff to reduce your body temperature. And the thing it does is it dilates blood vessels in your skin so that more blood gets to the skin, the surface area, so you can exchange heat better with your environment. And then you do this amazing thing that humans are very proficient at, which is that you sweat. Um, and so one of the reasons those Finnish saunas can get to such a higher temperature than the steamy saunas is because you have evaporation of sweat, which is cooling you off, whereas if you're in steam, your sweat won't evaporate. Um, so people can tolerate the the Finnish song is quite a bit better because of sweating. You can lose a lot of water through sweat though. You can put out liters of water in a hot enough sauna if you spend enough time there. So dehydration is certainly something to think about. There have been some studies that show that that warmth does release some endorphins, which are sort of endogenous, feel good chemicals. So taken all together, it's not as like, oh my God, I'm about to die as a cold plunge, but still might not be pleasant for you. Emily.

Emily: [00:22:59] I don't like it.

Perry: [00:23:01] All right. Um, okay. So now we know what happens, right?

Emily: [00:23:04] Question is whether it's important.

Perry: [00:23:06] Whether it's helpful. Biologic plausibility wise. There's something here. It does something right. It may be increasing. Your heart rate is good. It's like a little exercise. You know, vasodilation, vasoconstriction. You could make arguments that these are good things, but we really need to figure out like, okay, are they good things. And I think where ice has got its, uh, most data, Emily, is for for athletes, right? Like, particularly like athletes who are really doing endurance stuff. Can you tell me about that?

Emily: [00:23:36] Yeah. So I think both ice and heat are things that people who are doing, like serious sports try to experiment with. And I think we sort of start with Ice. The idea again, to get to the biological plausibility issue is the idea behind ice is sort of similar to like, I have an injury I have, which partly is inflammation. You ice your injury. That's like a well-known approach to injury prevention. And I think there's a kind of extension into the sort of cold plunges and icing, which is like, well, maybe if I just iced my whole body, that would lower my inflammation overall. And it might improve recovery and ideally improve performance. I mean, I think part of what's my guess is we'll talk about this a lot in the podcast, but there's actually a lot more research on a lot of these topics in athletes than there is in other people, in part because it's a very easy population to study because you know what you're trying to achieve and it's short term. So you can say, okay, I'm going to put people in this protocol, dump them in the ice after their cycling test, you know, every day for three weeks, and then I'll do it not for three weeks, and I'll measure their VO2 max on a special bike and blah, blah, blah. And it's just much easier to think about what you're trying to accomplish and how to measure it. Yeah, and so many of the problems we have studying regular people is what we're trying to say is like, do you live to be 100? And like, I can't measure that three weeks from now, obviously.

Perry: [00:24:54] Exactly.

Emily: [00:24:55] So I will say, when we look at ice, my sense of the literature is that it's really not that great that these cold plunges, maybe they have, you know, a little bit of an, of an impact on sort of subjective muscle soreness, but in terms of recovery and performance and so on. There just isn't much consistent evidence that these things matter. Um, a lot of the studies have this feature that it's like, well, we did this and we looked at these, you know, 47 different outcomes and, you know, three of them. It mattered. And it's like, yeah, but that's actually not a very statistically robust result. So I for me the like ice for athletes is a bit of a dud.

Perry: [00:25:37] Yeah. I you know, as I was looking into this, I sort of assumed that at least for the real, you know, real athletes. Right. Like the professional athletes because you see these like the football players and the baseball players with the professional trainers and everything like, and they have these ice baths in the training house. And I saw enough videos of professional athletes, like talking about their process before they get into the ice bath, like what they have to go through mentally and physically. You know, they're like, okay, I've got because they hate it, right? Like, they've got to mentally prepare like some of them are drinking really hot tea. They're putting on like rubber gloves and boots and things like that so that they don't get like ischemia of their digits and things. And then they, you know, they get in and it has this feeling like, well, it must be really beneficial because they're they're putting themselves into this. And and you're right, you know, looking at the data, I couldn't find much. I found one study that looked at the level of a substance called creatine kinase, which is a muscle enzyme. It goes up when you work out really vigorously because you do damage muscles when you work out hard. In fact, that's the way your muscles get bigger is that you sort of damage them. And then they get they come back stronger. And so CK levels go up after exercise. And the people that they randomized to do the ice baths, it didn't peak quite as much. But I'm not sure that means that like that's even better for you right. Like yeah. Don't you kind of want some muscle damage? I mean, that's right. Like, if you're trying to build muscle.

Emily: [00:27:09] I mean, yes, you do need to damage your muscles to try to build them. But I think that more generally like where's the where's the performance outcome there. You know, this is like we're measuring all of these things and like, we don't really we don't have a great sense of that. That translates into performance. And I think if you look at the sort of true performance stuff, being cold is just we just don't have a lot of good evidence.

Perry: [00:27:29] All right. Professional athletes take note.

Emily: [00:27:31] On the other hand, I will say I think the evidence on heat in sports is somewhat more compelling. Um, the typical protocol here is hot tub. So basically taking people and after their workout, putting them in a hot tub for 30 minutes.

Perry: [00:27:46] This is literally the opposite of what we just talked about. So I feel like both of these can't work.

Emily: [00:27:51] People don't like this either. Um, and actually in some of these protocols, they make the hot tubs really hot. Uh, like, instead of your, your hot tub supposed to top out at, like 104 degrees, but they like the hot tubs up, so they go up to 107 and then they're like leaving these people. It was like, sounds horrible. But you do see some performance impacts there. And in particular for people who are going to like race in a hot environment. And now we're in like a really, really niche area. But if you're like training in someplace cold, but you're going to race someplace hot. There's a lot of benefits to heat acclimation, which you can do in a bunch of ways, one of which is the hot tub. So, you know, this is like a I would say there's more evidence for being hot than there is for being cold. But we are still talking about very small, like if if people are listening to this and they're like, I'm a recreational runner and I have like, I'm, you know, I'm trying to like run A5K like you don't need to. The best use of your time is just to exercise and have your regular life, not to get in the hot tub. We're talking about, like if you are, you know, a sub elite athlete and you're interested in adding something, I'd add sauna instead of adding cold.

Perry: [00:29:03] Let's talk a bit about for us non-athletes, I have to represent my people. You mentioned that the Finns put out a lot of sauna data, um, some of which is fairly positive when it comes to things like mental health and whatnot, which I always I was getting a little suspicious when, like, all the data on something comes from the country that's really invested in it. It's like if the, you know, if the Dutch put out like a lot of positive clog studies or something like. Right. Um, so we'll take it with a grain of salt. Finland. But, um, in terms of subjective well-being, it seems like these saunas are are good, right? I mean, it's a relaxing thing. Maybe for some people.

Emily: [00:29:42] Yeah. I mean, so my I think the most famous paper on this is a paper about Finland in which they looked at long term mortality, follow up for men in Finland who spent different amounts of time in, in the sauna. And, you know, we'll talk a lot about studies like this, but there are limitations to a study where you are using what's called observational data. So people weren't randomized. There may be different features between the people who spend seven days a week in the sauna versus two days a week in the sauna, but they find pretty in that observational data. There are quite large impacts On cardiovascular mortality, and it's not inconsistent with some randomized data about cardiovascular improvements and other things like in the heart space as a result of exposure to some of these temperatures. So I think there's like there's sort of a cardiovascular plausibility there. I mean, I'm curious if that lines like another way to think about quality of evidence here is to ask whether that effect, which sort of seems to be really a kind of cardiovascular effect as opposed to something else, like it really seems like it's something about the cardiovascular system. Does that line up with what you'd expect based on the physiology of the of the heat?

Perry: [00:30:57] Yeah. Yeah. I mean, it does seem like, uh, sauna ING is sort of a mild cardiovascular stressor. It kicks your heart rate up. It's almost like light exercise in terms of blood pressure changes and heart rate changes. Emily, I see you smiling because. And you're right, it's not as good as actually getting exercise. No, but. Yeah, but but cardiovascularly there is some of that. This introduces both an opportunity and a problem. The opportunity is. Yeah, okay. Maybe it is good to get your heart rate up a little bit however you can. I suspect it's better to get it up by walking around the block a few times than by sitting in a sauna, but it's not nothing there. The other thing is something we always worry about in epidemiological studies, which is reverse causation, where people who have some cardiovascular problems might not be able to tolerate the sauna as much. And so then when you kind of follow people over time and you're like, oh, people who do more sauna live longer, when in fact it's people who are less healthy, do less sauna to begin with. Which sort of complicates the issue. But I don't think it's inconceivable that either the cardiovascular benefits or I'm a big believer in the power of like doing something intentionally for yourself. Um, and there's a lot of stuff in this space where I think it's that it's like, okay, this is me time, right? Like I'm getting in the sauna. I'm not bringing my phone. I'm just sitting and with alone with my thoughts. And maybe you don't even need the heat. Maybe it's just a quasi meditative state that I think actually might be beneficial for mental health.

Emily: [00:32:27] Do you think the same about the cold plunges, or is that.

Perry: [00:32:30] No, not at all. No, because I think in the cold plunge, I think instead of like quietly being with your thoughts, your brain is like, what are you doing? Please leave this horrible place. You're about to die. I'm shutting down your body systems as we speak.

Emily: [00:32:43] Yeah, that's what I think. So one of the things people will sometimes talk about is the idea that saunas are a detox, that they're. You're sweating out the toxins. A lot of efforts to get rid of toxins. So do you think that if you sweat more, you get more of your toxins out? And what are the toxins specifically?

Perry: [00:33:01] No no no no, not not not a chance at all. Um, you have two organ systems that are designed to detoxify you. The liver and the kidneys. That is their entire evolutionary purpose. They do an amazing job. Sweat is 99% water. The other 1% is salt, sodium chloride. That's what sweat is. So you will lose water. You will lose salt. Both of these are things that nominally you need to survive. And so we would want to replenish those after asana just to put some numbers in it. There was a study that looked at the excretion of organic pollutants in sweat. So if we're worried about toxins, here's a good one for you. Right? It's the stuff that we spray on crops and things like that in our system. It gets in our blood. You can measure these things. And so took some people, put them in the sauna, tested their sweat, and they determined that if you were to leave people in the sauna for an entire day and somehow they survived. So, you know, getting a ton of sweat out of these people, you would excrete through sweat 0.01% of the daily accumulation of organic toxins. So there is a measurable and tiny amount, but it is spitting in the hurricane of potential toxins that are out there to try to excrete it via sweat. That's not what sweat is designed for. That's what urine is designed for. That's what bile is designed for. You have organs that do this. Sweat is designed to cool you off. It is extraordinarily good at this. If humans are these amazing animals that evolved on the African plains to do persistence hunts against animals that can't sweat as efficiently as we can, and we maintain our cool under the African sun, and they collapse of heatstroke and then we kill them. Like that is where we come from. That is what sweats for, not to get your toxins out. Sorry.

Emily: [00:34:55] Okay. But I think what people have noticed is a good story about the gazelles. Um, but I think what people have noticed is like, if you drink a lot at night and then you go into a sauna the next day, you smell like vodka. And that I think people perceive that to be like, you know, cleansing them from toxins. So is that why is that?

Perry: [00:35:17] Alcohol is special.

Emily: [00:35:19] Alcohol is special. I totally agree. Say more.

Perry: [00:35:21] Alcohol and water. Do not know that they are different chemicals from one another. So virtually throughout the body, alcohol and water are freely exchanged in the solution of your body. So whatever your blood alcohol content is, is your sweat alcohol content. It just they go together like that. Um, now it's not much, but it is enough to potentially be detectable. Again, it is not enough to clear alcohol from your system by any stretch. You have an organ that is designed to do this. It's called your liver. Your liver can clear for an average man. And it varies. But about a drink's worth of alcohol per hour from your bloodstream. Don't try this. It gets worse the more tricks you have sweating in a sauna. You know, we're talking less than 100th of that amount. It's just not the way to to get alcohol.

Emily: [00:36:19] It's just not the hangover cure that one hoped for.

Perry: [00:36:22] No, it's definitely not. In fact, the dehydration that comes from a sauna is probably going to make things worse.

Emily: [00:36:28] Also make things worse. The last thing I wanted to say on the benefits is, um, I came across what I think was an extremely interesting study about women with obesity and PCOS, where they did it's a it's a relatively small study, but they did actually a pretty short, uh, intervention where they sort of put them in the hot tub for an hour a week for 8 to 10 weeks. And there actually were a bunch of improvements in blood pressure and other like, cholesterol metrics. So no improvements in weight, but just things that looked like, as you said at the beginning, like a little bit like they had exercised like similar to if you had put people in exercise. So, you know, I think part of what was interesting about that for me was, you know, I think exercise is great, but exercise is not always feasible for everybody and is not something everybody wants to do. And so to the extent that there's a this is sort of something that could be helpful in some cases, maybe on the way to exercise or maybe in addition to it, it feels like there's there's sort of something there that might be meaningful enough that it's worth considering for some people. I buy it, okay, but not all people. So what when we sort of talk about are there people who should not do this pregnant?

Perry: [00:37:47] Yeah, yeah. There's always people who should not do everything. Um, you know, again, if you're curious, if you're one of these people, of course, talk to your doctor. But broadly speaking, both of these hot and cold are mild cardiovascular stressors. So people with pre-existing heart disease who are at risk of heart disease, you know, certainly can be put at risk by going into either of these situations. People at risk of arrhythmias, particularly with the cold plunge. And I'll just say it again, I would not put your face in the water when you're in the cold plunge. The problem with arrhythmias is that a lot of people who are at risk of them don't know that they're at risk of them at least the first time it happens. And so it does make me a little bit nervous, obviously, jumping into a cold body of water, as opposed to like a tub in your backyard has extra dangers because of that cold shock response. You know, people jumping into cold lakes can just, like, go under and not come up, and it's very hard to find them. Deaths have been described. So, you know, this is something to take seriously and carefully. I will also mention that there have been some studies. If you're a man that is interested in fertility, at least in the short term, that prolonged exposure to heat does kill sperm. Um, and so if, you know, if you're, you and your partner are trying to get pregnant, it's probably not the best time to do significant sauna or hot tubbing. And women who are pregnant, uh, that elevated body temperature can certainly be damaging to the fetus. And so we don't recommend hot, uh, certainly for pregnant women. And I probably wouldn't recommend cold in that case either.

Emily: [00:39:27] Disagree. Actually, I spent a bunch of time at some point looking at the cold plunge data in pregnancy. And I would say, although, you know, of course the data is limited because cold plunging seems terrible. And why would you do it ever? Um, there actually are there is some evidence on this, actually no real reason to think that, you know, particularly if you are a person who generally does this, that you would need to stop doing it when you were pregnant, which is not the case of hot tubs and saunas, where the risk for neural tube defects, particularly for exposure in the first trimester, means that that's a no no.

Perry: [00:40:03] Fair enough, fair enough. All right. No saunas. Maybe cold plunges, but be careful.

Emily: [00:40:07] So my last, like, uh, risk question that I have always wondered about is like, can you get frostbite from being in the like, if I get in and I have some exposed parts, fingers. Toes for men. I mean, aren't you worried your penis is going to get frozen off? Honestly, isn't that a thing you're worried about? I would be worried.

Perry: [00:40:28] Well, I hadn't thought about it until just now. Well, now I'm worried. It's not. It's not my go to every time. Geez. Um, so typically in frostbite, we imagine that it occurs when the external temperature is below freezing because you have ice crystal formation. So that being said, you can get ischemic digits. Um, so that response to cold is that the blood vessels in your, your superficial blood vessels constrict and it can be quite powerful. Particularly there's a phenomenon called Raynaud's phenomenon. Many women have experienced this where.

Emily: [00:41:09] It's horrible.

Perry: [00:41:10] And I mean men have it too. It's just more common in women where you have such severe vasoconstriction in your finger. Typically fingers. But it can happen in toes too, that it's just white. There's just no blood flow there. Um, that can be triggered by cold plunges. And so many people who do this routinely actually wear like some rubber gloves and rubber booties and even rubber boxer shorts to get to the issue that you are, um, referring to Emily, to try to make sure that those nibbly bits, as we call them in the medical profession, don't get exposed to too much of that cold. Um. Broadly speaking, I think if you're healthy and you don't have vascular problems to begin with, even some vasoconstriction from the cold plunge that you know is painful and hurts is not going to result in the loss of a digit the way you could if you were outside in subzero temperatures.

Emily: [00:42:03] You won't lose your fingers, but your nibbly bits could be uncomfortable. Thank you.

Perry: [00:42:08] Yes. I'm sorry to use medical jargon. Well.

Emily: [00:42:11] It's fine. I think we're going to be using that in the future. Um, okay. So, Perry, what is your one thing? Take away. On cold plunges and saunas for the listener.

Perry: [00:42:25] Cold plunges. Seems like modern day self-flagellation. Be kind to yourself. I don't think it's worth it. Saunas? Sure. Go for it. Primarily because it's a nice time to have some time to yourself and relax, which we all need more of.

Emily: [00:42:39] My one thing is similar. What I would say is if hot tub sauna on a regular basis sounds like something that would serve you emotionally or in some other way, then that seems lovely. And in fact, if getting in this ice tub in your backyard would serve the same things, and that's a nice date. That also seems fine up to the concerns, but for most people, I don't think I would invest in either of these for significant health benefits. There are a lot of other things I would put on the list for people first.

Perry: [00:43:15] Sounds good. We will be back right after this with your questions. And we're back with our listener question of the week.

Ellie in Toronto: [00:43:29] Hi Emily and Perry, this is Ellie from Toronto, Ontario. So I'm a parent, uh, in my late 40s, and I've been running on about, I don't know, 5 or 6 hours of sleep a night for, uh, well, many, many years. Um, so my question is, I function, you know, I mean, I get through my day, I've convinced myself that I've totally adapted to that amount of sleep, and it's fine. Um, but I keep hearing that chronically not getting enough sleep, um, can kind of damage your health quietly. And so I'm wondering, is regularly getting this amount of sleep harmful if you feel fine. Like, what does the research say about, you know, long term effects on things like, you know, like my metabolism or my heart or my mood, my weight, etc.. Um, and then I guess the last piece is if someone can't realistically get eight hours, what are the most meaningful ways to reduce the damage? Thank you.

Perry: [00:44:34] Emily, I'm so excited about this question because I get to talk about familial, natural, short sleep. Um, one of my favorite and most awesome genetic conditions. So there are people out there, literally, who do not need to sleep, uh, as much as other people. Approximately 1% of the population have this genetic condition called familial natural short sleep. Um, I will point out that it's not a syndrome or a disease because it doesn't cause any problems. In fact, it seems to be quite beneficial. These people need to sleep about 4 to 6 hours a night. They suffer no ill effects. Um, they might even be protected against Alzheimer's disease. There's some suggestion there. It is inherited through families. But the fact is, unfortunately, that most of us aren't lucky enough to have the special genetic mutation that prevents dementia and makes you not have to sleep at night.

Emily: [00:45:26] How would I know? So before we get into regular people, how would I know if I had this mutation?

Perry: [00:45:31] You might know because you sleep 4 to 5 hours a night and feel completely fine. Or at least you might be. You might suspect. And then many of the genes are actually known. So if you if you were genotyped, they could detect that you had this variation.

Emily: [00:45:44] That is fascinating. However, most of us do not have this variation, and most of us need more than this amount of sleep that this person is getting. I mean, so first of all, I just think we underestimate how important sleep is. I think most adults, especially adults who have jobs and kids and etc. kind of think of sleep like a, a sort of nice to have, you know, sort of like a pedicure. Right? Like, you know, it'd be great if I could get one. My feet would look better, but like, if I can't get one, it's totally fine. And I sort of think people should think of sleep much more like a biological necessity. Like. And if you don't get enough sleep, it's like torture. I mean, sleep deprivation is a form of torture. And we know that people's working memory and executive function is affected by even relatively limited limitations on amount of sleep. So they have these studies where they'll take away a couple hours a night for some period of time, and over a few days of that, you actually end up with a level of functioning that's not dissimilar to if you literally skipped a night of sleep. And it's especially hard on working memory, which is something that when you think, I need to do something and then you go into the other room and you've forgotten what it is. That's your working memory. And that's not good if you are not sleeping enough.

Perry: [00:46:58] Yeah, I couldn't agree more. It's super important. Most people need about six and a half to 8.5 hours a night. People do vary a little bit around there, but you really got to get it in there. You've got to prioritize it the same as you think about like getting some exercise or eating well or whatever. It is a critical thing to focus on, so do your best.

Emily: [00:47:14] I will also say, I want to recognize that it is really hard to get enough sleep, and that for a lot of people listening to this, you probably have multiple jobs and multiple children. And so this is partly, you know, giving yourself a break and saying like, hey, if I'm not in bed at 10:00, fully asleep and up at, you know, six like Brian Johnson, like it's okay. Like you're not going to immediately die. But it's also saying, you know, this should be something you prioritize. And so thinking about what is feasible for me to improve my sleep, I think that's something that we should care about. And I think at some point we should do a whole episode on the science of sleep. Because I love the science of sleep. Every animal sleeps. It's so interesting. Dolphins sleep half their brains at a time while they're swimming. So whatever. I'm going to pull out so many great facts for you. So, Perry, do you have any quick tips for better sleep if someone wants more sleep?

Perry: [00:48:06] The standard sleep hygiene stuff here, which is you don't want to drink caffeinated beverages, typically after like 4:00 pm. Um, you might not even want to drink any beverages as you approach 8:00 9:00 at night, just so you don't have to wake up in the middle of the night to pee. We want people sleeping in dark, quiet rooms as much as possible. Those noise machines and stuff can actually disturb sleep a little bit if you are in a loud environment. Earplugs are awesome if they're comfortable for you. Um, and the bed is a place to sleep and have sex, not to eat and watch TV and be on your phone and whatnot. I'm okay with reading in bed, but I would read an actual book as opposed to a phone, because that blue light that comes from the screen can actually keep you up a little bit.

Emily: [00:48:49] That's it.

Perry: [00:48:53] Join us next week when we ask, what's the deal with the blockbuster weight loss drugs GLP-1s?

Emily: [00:48:57] Wellness Actually is produced in association with iHeartMedia. Our senior producer is Tamar Avishai. Our executive producer at iHeart is Jennifer Bassett. Our theme music is by Eric Deutsch, and our content is for educational purposes only.

Perry: [00:49:14] If you like the show, help other people find us. Leave a rating and review on Apple Podcasts or your podcatcher of choice, and help us spread the word about the show. Don't give the TikTokers all the power. And don't forget we want to hear from you. Head over to wellness and leave us a question for our mailbag, or suggest a topic for a future show.

Emily: [00:49:34] We'll let the influencers have the last word.

Speaker7: [00:49:36] All right, guys, so I am three weeks into cold plunging and I'm going to explain to you guys the differences I'm noticing and whether I think this is worth it or not for you guys to go out and get a cold plunge for yourself or build one. But I've been doing it for three weeks now, every single morning. And I will tell you, the very first thing is that I highly underestimated how much I was not going to want to get into that cold plunge every day.