Sauna use has been associated with a variety of health benefits related to longevity. Regular sauna use has been shown to increase heat shock proteins, which can reduce inflammation and improve overall healthspan . Sauna use has also been found to be inversely associated with the risk of fatal cardiovascular events and all-cause mortality, with more frequent use showing greater reductions in risk . The optimal sauna duration is around 20 minutes at a temperature of about 174 degrees Fahrenheit . Sauna use can also have beneficial effects on the cardiovascular system, including reducing blood pressure and improving vessel function . Regular sauna use has been associated with a lower risk of dementia and Alzheimer's disease . It is important to note that sauna use may not be suitable for everyone, and it is recommended to consult with a medical professional before starting a sauna protocol .
Rhonda Patrick: 30 minutes increase their heat shock proteins by 50%. And once those levels are increased, they stay elevated for about 48 hours. It's also been shown in separate studies that people that are already acclimated to heat, as in they're frequently using the sauna, or they are frequently physically active, which also raises your core body temperature, they can increase their heat shock proteins sooner upon heat stress exposure and more robustly. So people that are heat acclimated actually get a better heat shock protein response. So with that said, I will mention one more thing, one more possible mechanism by which the sauna can improve overall longevity, and that is by lowering inflammation. Multiple studies have implicated that inflammation plays a major role in the aging process and also in age-related diseases like Alzheimer's disease, cancer, heart disease. So having something that can lower inflammatory biomarkers is something that is good for increasing healthspan. And the sauna has been consistently shown to lower, for example, C-reactive protein in a dose-dependent manner. So the more frequent the sauna bathing, the more longer the duration, the more robust in terms of lowering C-reactive protein. It's also been shown to increase anti-inflammatory biomarkers like IL-10. So that's also a very good thing, something that's also very consistent with physical activity as well. Physical activity has also been shown to do the same thing. That's pretty much all I'm going to talk about today. There's lots of other things the sauna improves. It's also been shown to have a major effect on brain function. And it increases endorphins, much like physical activity.
Rhonda Patrick: In fact, one of the more interesting observations made by Dr. Laukonen in this podcast is that time spent in the sauna appears to be a very important factor with shorter sauna durations having a much less robust effect. Okay, enough preamble. Let's get this show on the road. On to the podcast. Hello, everyone. I am in Finland sitting here with Dr. Jari Laukkanen. I'm a little excited to be sitting here with Jari because I've talked quite a bit about his research involving using saunas and how that has been shown to improve cardiovascular health and also improve overall longevity. To my knowledge, this is actually...your work is the first research that I've actually seen in humans to show that using the sauna, you know, can improve longevity. Maybe we can start off by talking about this study that you did on...published about a year ago, I believe, in the Journal of American Medical Association, JAMA. looking at the use of the saunas and sauna frequency and cardiovascular-related mortality and overall mortality rate. So can you tell us a little bit about the study itself?
(someone): Yeah, yeah, yeah. Thank you. Our study is based on middle-aged population from Eastern Finland, and at baseline, we measured the use of sauna, how many times per week and how long time per one session and what was the temperature. And on the basis of this information, we have studied the association between the use of sauna and fatal cardiovascular outcomes and mortality. And in this study we found really that sauna use was inversely associated with the risk of fatal coronary heart disease events and all-cause mortality.
Rhonda Patrick: Short-term stress can result in a reduction in long-term chronic stress. In other words, we can build resilience. This is because exposure to short-term stress can strengthen the cellular response mechanisms in the body to stress. This is called hormetic stress. Hormetic stress promotes longevity in part through enhanced activity of many different stress response pathways and defense mechanisms that kick in after the exposure to the hormetic stress. Some examples of hormetic stress include exercise, heat stress from the sauna, cold stress, and fasting. A recent study on around 2,000 middle-aged men found that using the sauna two to three times per week was associated with a 24% lower all-cause mortality, and using it four to seven times per week was associated with a 40% reduction in all-cause mortality. compared to men that only used the sauna one time a week. So there was a dose-dependent effect, meaning the more frequent the sauna use, the lower all-cause mortality that occurred. Because this is an association study, no causality can be established. However, the dose-dependent nature of the effect dramatically strengthens the study. So we must turn to animal studies in order to establish causality. Just one exposure to heat stress in flies and worms has been shown to increase their lifespan by 15%. The mechanism for this has been shown to be dependent on something called heat shock proteins. In fact, another study recently identified that aging is caused by a molecular switch about eight hours into adulthood of a worm that deactivates heat shock proteins. So when heat shock proteins are deactivated, this causes rapid cellular aging in C. elegans, which are tiny roundworms.
(someone): How long do you stay in there? So let's get into some of those details, and I'll preface this by saying this is not medical advice. Anyone that is considering using the sauna, good idea to check it out with your medical professional first in case you have a health condition that may make sauna use dangerous, but with that said, yeah, let's hear about what you've incorporated into your life.
Rhonda Patrick: Sure. Well, let's start with the studies and the data that I referred to and what the temperature, duration, etc. I talked a lot about frequency four to seven times a week, but I didn't talk much about temperature or how long people were in the sauna. So in almost all of those studies, the temperature of the sauna, these were saunas in Finland, and they were 174 degrees Fahrenheit around. And the humidity was between 10 to 20% humidity, I think, something like that. What was very interesting to me when I was looking at the data coming out of Dr. Yari Lakunin's lab is that duration in the sauna seemed to matter with respect to robustness of the results. So I mentioned, for example, you know, people that use the sauna four to seven times a week were 50% less likely to die from, like, you know, cardiovascular disease-related death. Well, that number was referring to people that stayed in the sauna greater than 19 minutes. So this was about 20 minutes. So 20 minutes is the sweet spot at about 174 degree Fahrenheit, you know, humidity 10 to 20%. People that sat in the sauna for like 11 minutes on average, their reduction in cardiovascular disease-related death from cardiovascular disease was like 8%. 8% versus 50%, big difference there.
Rhonda Patrick: damaged cells, and that leads to organ dysfunction ultimately. So FOXO3 is pretty awesome. I could go on and on. It's, you know, it's been shown in many different animals to regulate longevity. The more you have of it, the better. So heat stress from the sauna activates FOXO3. Exercise also activates FOXO3. I'm gonna circle back to the same study on 2,000 middle-aged men, which also found that fatal cardiovascular disease was 27% lower for men who use the sauna two to three times a week and 50% lower for men who use the sauna four to seven times a week compared to men who only use the sauna one time a week. I think it's important to point out here that sitting in the sauna the heat stress from the sauna. to some degree, mimics cardiovascular exercise. So some of the positive benefits of the sauna on heart health may have to do with similar benefits seen with regular physical exercise. So when you sit in the sauna and start to become really hot, heart rate starts to increase. And I've experienced this, you know, every time I'm in the sauna, every time I'm exposed to heat stress, heart rate can increase even up to 100 beats per minute. during moderate sauna bathing and actually can go up to 150 beats per minute during a more intense sauna session, meaning the hotter the sauna, the longer you're in there, which is really fast. And actually, 150 beats per minute corresponds to moderate intensity physical exercise. So I think that to some respect, some of the cardiovascular benefits from the sauna have to do with the fact that the heat stress does sort of mimic cardiovascular exercise to some degree.
Rhonda Patrick: So do you have any sort of parameters or guide that, you know, someone that's trying to figure out how long to stay in the sauna in order to get this sort of benefit, how long they should stay in? Probably depends on temperature as well.
(someone): Yeah, on the basis of this study we defined that 20 minutes could be enough, but at the moment actually we are exploring more carefully what could be the time needed to stay in the sauna. And it can be that very short time, let's say 10 minutes or 15 minutes, it's not enough to get all these health benefits maybe. So we try to clarify what is the optimal time to stay in sauna.
Rhonda Patrick: Great. So you're working on those parameters right now. What was the average temperature that the sauna that these men were using? How hot was it?
(someone): It was 79 Celsius.
Rhonda Patrick: So about 20 minutes in a 79-degree Celsius sauna was what was important for, at least in the context of the lower cardiovascular-related mortality and also all-cause mortality as well.
(someone): Yeah. That was our primary finding.
Rhonda Patrick: What was the type of sauna that these men are using? Because this is Finland, right?
(someone): Yeah, it's Finland, yeah. For us, it's clear that it is Finnish dry sauna. Yeah, it's relatively dry.
Rhonda Patrick: Relatively dry? Yeah. So they weren't doing that... What's it called when you dump the water on? Löyly. Löyly. Yeah.
Rhonda Patrick: But using the sauna four to seven times a week, it's associated with between a 60% to 66% reduction in dementia and Alzheimer's disease compared to people that use the sauna one time a week. So it seems like, you know, four times a week is kind of the sweet spot, and we can talk about all the details of that in a little bit. But there's a lot of interest into why sauna use seems to help prevent neurodegenerative diseases like Alzheimer's disease and dementia. So I certainly have some hypothesis and hypotheses, I guess. They're more than one. So I'd love to dive into some of that. But I think that's a kind of a good start into the sauna. Oh, and also all-cause mortality. That's a really big one too. you know, there's been these studies, these large population studies finding that people that use the sauna four to seven times a week have a 40% lower risk of dying from all causes of death than people that use the sauna one time a week. So to me, it really is the beginning of understanding that, you know, sauna use seems to really be beneficial for our health. And much like a lot of these lifestyle factors that are well-known to modify our disease risk, so exercise, for example, so you don't want to be sedentary, good sleep, you know, a healthy diet, meditation. I think these are pretty common knowledge at this point to be beneficial for overall health. And I think that sauna use should be up there. I think it should be included in that sort of, you know, bag of things that are known to improve what's called our health span.
Rhonda Patrick: I mean, getting out when you just experience the most slight bit of uncomfortableness, maybe not the way to go. But like, you know, when you're in there, you know, like you're feeling like this is... I'm getting really hot. And again, like once you hit the 20-minute mark, That's really all that's needed, you know, 20 minutes, 174 degree Fahrenheit. That's what all these studies have shown have been beneficial for reducing cardiovascular disease mortality and all-cause mortality and Alzheimer's and dementia risk. So that's, I think, a pretty good rule of thumb as well, you know, 20 minutes. And you can also have a timer. Outside of your sauna, I used to do that. I used to have a timer clock and it's like, okay, I reached my time. So that's also another option.
(someone): I think it's good to have an alarm because sometimes, you know, you can fall asleep in there. It can be pretty comfortable, especially after you're heat adapted. So I'm a big fan of the alarm to let me know that like 25 minutes are up.
Rhonda Patrick: Yeah. If you're prone to falling asleep in the sauna, you should always have someone with you in the sauna, for sure. Because that could be dangerous. Yeah. And I know you wanted to cover this, Kyle, the contraindications of sauna use.
Rhonda Patrick: And I think that sauna use should be up there. I think it should be included in that sort of, you know, bag of things that are known to improve what's called our health span. Our health span is It's basically compressing the diseases that we get into a shorter time period. So it's essentially extending the youthful part of our life. So you may not necessarily live, you know, X many years longer, although you may if you don't get cancer earlier, you'll probably end up not dying from cancer earlier. But ultimately, improving your health span is about improving the quality of your life, not getting Parkinson's disease, not getting Alzheimer's disease, not getting cancer, not getting cardiovascular disease, type 2 diabetes, and having a better quality of life so that you're essentially enjoying your life and living healthier for a longer period of time. I do want to make sure to distinguish the difference between my publication on the sauna, which was a very comprehensive review article covering multiple aspects of sauna health, and someone doing primary research where they're actually doing experiments and having people, you know, come into a sauna and measuring heart rate and blood pressure changes, for example. So I am not doing those experiments. And a lot of the research that has been done on the health benefits of the sauna have actually come out of Finland from Dr. Jari Laukonen's lab in eastern Finland. And so I just wanted to give him a little shout out because his work has been invaluable in our understanding of the health benefits of the sauna.
(someone): let's start by diving in a little bit deeper into the cardiovascular system, because you mentioned there's some potentially excellent benefits from the sauna on the cardiovascular system.
Rhonda Patrick: Today's podcast features a conversation I had when I was in Finland with one of the world's foremost researchers of the sauna, Dr. Jari Laukkanen. Jari holds a PhD and an MD. What makes this conversation very interesting is that Jari not only comes to it as an actual researcher of the sauna, but also as a cardiologist. Often when I talk about the sauna, I may sometimes refer to animal studies, especially when it comes to molecular evidence, but it is Dr. Laukkanen's lab that actually makes the single most convincing case that sauna use has real benefits in humans. It is his research that has shown that long-term sauna use appears to reduce heart-related mortality, but even more surprisingly, also may have a strong effect on what is known as all-cause mortality, which literally means death from all causes, which sounds a whole lot like longevity if you think about it. Moreover, since this conversation was recorded, Dr. Laukkanen's lab released yet another publication, which showed a really strong association with the reduction in the risk of dementia and Alzheimer's disease by 66% and 65% respectively at a 20-year follow-up, which further strengthens the case that sauna therapy may be more than just relaxing, but may actually be a great tool for even improving health span. In both the studies showing reduced memory illness and reduced all-cause mortality, The effect follows a dose response relationship with the group showing the strongest reductions in risk by frequenting the sauna at least four times a week for at least 20 minutes at 174 degrees Fahrenheit or 79 degrees Celsius. In fact, one of the more interesting observations made by Dr. Laukonen in this podcast is that time spent in the sauna appears to be a very important factor with shorter sauna durations having a much less robust effect. Okay, enough preamble.
Rhonda Patrick: So that's kind of the agenda today. All right. So over the past few decades, there's been emerging research, very compelling research, observational studies, prospective studies, interventional trials, as well as mechanistic studies that suggest that sauna bathing improves overall health. And we're going to talk about at least sample a few of all those types of studies today. So probably some of the largest perspective studies have come out of eastern Finland. And they're using a cohort of people that is part of a study called the Kupio Ischemic Heart Disease Risk Factor Study. And that study is a very long, ongoing perspective study that started back in the 80s. It includes a few thousand individuals, men and women. And people are followed for 20 years or so and a variety of different diseases are looked at. So a study was published a few years ago in the Journal of American Medicine, JAMA, Internal Medicine, sorry. And what that study looked at was, in this specific case, it was men, about 2,300 men, that had at least one risk factor for cardiovascular disease. And it looked at sauna bathing and its overall effect on longevity, as well as a variety of different cardiovascular related diseases. And what it found is that, Sudden cardiac death, so looking at sudden cardiac death, men that use the sauna two to three times a week had 22% lower sudden cardiac death compared to men that use the sauna one time a week. Men that use the sauna four to seven times a week had a 63% lower sudden cardiac death compared to men that use the sauna one time a week. So there was a dose-dependent effect in terms of frequency.
(someone): What temperature should the sauna be? How long should we stay in it? How often should we use it? So really excited to jump into this, but I want to give you a brief introduction first. You have a PhD in biomedical science. You're published in a variety of reputable journals, including an excellent recent publication on saunas. That was very comprehensive. And you're the co-founder of a popular website and YouTube channel called Found My Fitness. Dr. Patrick, welcome back to the show.
Rhonda Patrick: Thank you, Kyle. I'm really excited to be here. And thank you for that very kind introduction.
(someone): I look forward to getting into as many details as possible about both the benefits and how we can effectively use saunas. But first, if you only had a couple minutes with someone who was totally new to saunas, how would you briefly summarize the benefits?
Rhonda Patrick: Well, I would start with a lot of the studies that have come out of Finland, which have been, you know, very, very large population-based studies. These are observational studies where an association has been made. And there have been quite a few that have found that frequent sauna use is associated with a lower risk of death from cardiovascular disease, a lower risk of sudden cardiac death, a lower risk of coronary heart disease, a lower risk of stroke, a lower risk of dementia, of Alzheimer's disease. And when I say a lower risk, it occurs in a dose-dependent manner. So what that means is the more frequent the sauna bathing, the more robust the health benefits are.
Rhonda Patrick: So, you know, if you can do something that lowers your risk by, you know, 50%, I mean, that's very significant. What do you think...I have my own sort of, you know, I've done some reading on how the sauna affects in different vascular functions, but you're a cardiologist, so do you have some sort of...do you speculate on some of the mechanisms by which using the sauna can improve cardiovascular health?
(someone): Yeah, we have been studying also these mechanisms, which can be explained to our findings. And one of the most important is the blood pressure, because sauna use, long-term sauna use, can decrease blood pressure level. Actually, we have studied in the same population and found that there is a reduction of incident hypertension among those who are using more sauna compared to those who have only, let's say, one session per week. And so blood pressure is one of the most important factor which can explain the findings.
Rhonda Patrick: And do you know why sauna lowers blood pressure?
(someone): There may be many reasons. We know that it can balance autonomic nervous system as well and also it can improve the vessel function.
Rhonda Patrick: Endothelial cells?
(someone): Yeah, endothelial cells. And another thing is that sauna may have some effect on arterial stiffness and compliance of arteries can improve after a long-term sauna use.
Rhonda Patrick: Wow. So a lot of these parameters that you just described are also known to be affected by cardiovascular exercise, right? Aerobic exercise. So I have to mention that, like, you know, as a
Rhonda Patrick: I look forward to that. The other one, which I won't get into too much detail because I don't want to talk so much, but it affects endorphins. So sauna releases endorphins. Endorphins make you feel better.
(someone): feel better, yeah. It is relaxation, yeah. Also in Finland, I think quite many youth for that purpose, they want some relaxation, you know, after working day and so on. It's like a happy to end your day and go to sauna and after that you feel more relaxed.
Rhonda Patrick: Do you think that may also have something to do with the improved longevity? Because stress is also linked to longevity, and so if it's something that's lowering stress and making you more relaxed, then that seems like it goes hand-in-hand with longevity as well.
(someone): Yeah, can be. And there are studies showing the role of autonomic nervous system and cardiovascular diseases, how they are related together. And also in our study we want to explore how the sauna may have effect on heart rate and heart rate variability, which is one of the measures which can be used to assess the autonomic nervous system and its function.
Rhonda Patrick: Having been in Finland now for a few days and having the privilege of going to the Finnish sauna society and also hanging out with some other friends here in Finland, I've had a chance to experience the sauna culture, the traditional smoke saunas and also the other dry saunas and the loulu. But what I also noticed is that almost 100% of the Finnish people that use the sauna after the sauna, like to go run into and jump into a cold lake or the Baltic or something cold, very, very cold.
Rhonda Patrick: Aerobic exercise. So I have to mention that, like, you know, as a someone that uses the sauna, when you sit in the sauna for, you know, a long enough period of time, your heart rate starts to elevate as if you were doing cardiovascular work. In fact, I think it's something like 100... 120 or 150 maybe.
(someone): 150 beats per minute? Yeah. It is quite high, actually. It is something like the moderate level of physical activity.
Rhonda Patrick: So you mentioned the duration, the time people spent in the sauna also was an important factor on the robustness of lowering cardiovascular-related mortality. So people that stayed in the sauna, I believe it was longer than 19 minutes had the most robust effect compared to men that stayed in less than 11 minutes.
(someone): Something... Yeah. The risk reduction can be seen among those who were more than 20 minutes per session in sauna. There was a risk reduction among those men.
Rhonda Patrick: Yeah. I'm always sort of hesitant to tell people, They ask, you know, well, how long should I stay in the sauna? Because on the one hand, you don't want to stay in too long, but you also don't want to not stay long enough to get these important benefits, these cardiovascular benefits. So do you have any sort of parameters or guide that, you know, someone that's trying to figure out how long to stay in the sauna in order to get this sort of benefit, how long they should stay in? Probably depends on temperature as well.
Rhonda Patrick: I don't. That's something that I probably should read up on.
(someone): Because they don't get quite that hot, but there's a lot of long time in a very hot water environment.
Rhonda Patrick: Right. And so I think this is a good opportunity to mention that there's other modalities for increasing your core body temperature, not just a finished sauna or a dry sauna or infrared sauna. There's steam showers, there's hot baths. And there's been studies comparing hot bath to a dry sauna in terms of some of the endocrine effects. The sauna has profound effects on the endocrine system. And those effects are very similar in terms of a hot bath versus a sauna. So I mean, for me, I'll take hot baths at home, but it's so easy for me to stick my legs out or my arms out. And so I'm not getting, it's better if you can stay submerged under the water. You want the benefit of that heat stress. When you start to cool certain parts of your body off, it's not working quite as well. So I find for me, getting myself in the box where I can't escape anything works best. But I absolutely think that the hot baths have similar effects. Any other questions? Oh, yes, of course.
(someone): So, um, is there an age limit on the saunas, like for children? One question. And then the other question is, do you have like a quick rundown of some of the other tools for the increasing your health span that you were possibly going to speak about earlier?
(someone): One question. And then the other question is, do you have like a quick rundown of some of the other tools for the increasing your health span that you were possibly going to speak about earlier?
Rhonda Patrick: So the question about age limit in the sauna, of course in Finland the sauna is ubiquitous and many age groups are using it, children, adults. For the children there seems to be a limit in terms of time, so it's like much shorter duration, I mean like maybe like five minutes versus an adult that will sit in there for 20 minutes. I do have some scientific resources on my website, foundmyfitness.com. There's a topic page on the sauna, and it talks all about special populations, elderly, children. It talks about people with various heart-related conditions, as well as pregnancy. It's something to consider when you're talking about using something like the sauna as elderly people and children. That was a great question. And so your second question is some of the other topics that, some of the other tools that I think can help improve healthspan. So typically, I would say that there's a few things that I think have the biggest bang for your buck kind of thing. And I think that one of those is time-restricted eating. I think that time-restricted eating refers to eating all your food within a certain time window. and not eating outside of that time window. And that time window typically is anywhere between six to, I would say, 11 hours. You want to eat all your food within that time window and fast for the remaining time. The reason I say that is because, one, it's a lot easier for people to do that.
(someone): And on the basis of this information, we have studied the association between the use of sauna and fatal cardiovascular outcomes and mortality. And in this study we found really that sauna use was inversely associated with the risk of fatal coronary heart disease events and all-cause mortality. And after adjustment for other risk factors, which have been also measured in this big population-based study, there was still significant association between the use of sauna and these outcomes.
Rhonda Patrick: Yeah, so if I remember correctly, your study showed that men that used the sauna two to three times a week had a 27% lower cardiovascular-related mortality compared to men that used it one time a week. And men that used the sauna four to seven times a week actually had a 50% lower cardiovascular-related mortality than men that used the sauna one time a week. And that is very robust. I mean, so you followed these men for 20 years?
(someone): Yeah, the total follow-up time was 20 years and we have annually measured new outcomes and we have followed carefully from baseline until the end of the follow-up. And yes, the risk reduction was really, really obvious and clear.
Rhonda Patrick: Yeah. And you said you adjusted for other risk factors, meaning like obesity, you looked for people like obesity, smoking, alcohol, cholesterol, type 2 diabetes, these sort of factors, if I remember correctly. You also looked at socioeconomic status and physical activity, which is important. So, these were all...the data is reflective really of sauna use, not, you know, because people that use the sauna tend to also exercise more. So, you know, you have to correct for all those other possible confounding factors, which you did. So, the cardiovascular rate of mortality, were there certain...like, were you measuring
Rhonda Patrick: you know, I'm not convinced. So next question, what about the duration, frequency, timing of the sauna? If it's a typical sauna, like a dry sauna or a wet sauna that's really hot, somewhere between 170 or 180 degrees Fahrenheit or 77 to 82 degrees Celsius, then a duration of around 20 to 25 minutes is really what most studies have shown to be beneficial. And I typically stay in for about 25 minutes in a really hot sauna. As for the frequency, as I mentioned previously, there's a dose-dependent effect on both all-cause mortality and on decreasing cardiovascular-related mortality. So four to seven times per week was better than using it two to three times per week. Most of the studies on endurance and muscle atrophy were in the two to three time per week range, which is, I think, for me, at least, you know, doing it three times a week is more reasonable. In terms of timing, before or after a workout, all the studies that I spoke of today were done either after a workout or on days with no workout. I tend to do both of these. Practically speaking, doing this on immediately before a workout seems just awful. Really, who wants to be drenched in sweat and exhausted before the start of a workout? So I think it's pretty common sense. What about using the sauna during muscle injury? Well, as I mentioned, rats that were exposed to a 30 minute heat treatment or. Yeah, it was a 30 minute heat treatment at around 105 degrees Fahrenheit or 41 degrees Celsius increased their muscle regrowth and their soleus muscle by 30 percent after disuse.
Rhonda Patrick: Weyon therapy, which uses far infrared dry saunas, also has been shown to improve lung function in patients with chronic pulmonary disease, also known as COPD. The temperature of far infrared saunas are significantly lower than typical Finnish saunas, so they're typically around 140 degrees Fahrenheit. Since the temperature is lower, the duration in many studies is longer, around 45 minutes, and the frequency in many studies is daily for a few weeks. One of the major differences between dry saunas or finished saunas and far-infrared saunas is that both dry and finished saunas, the heat, the ambient air, and that heat is transferred from the air to the body. But in far-infrared saunas, the thermal radiation is directly used to increase body temperature. Sauna bathing was shown to reduce the incidence of common colds in 25% participants that use the sauna one to two times per week for six months compared to 25 controls that did not. It took three months before the sauna had a protective effect. The mechanism by which frequent sauna use reduces the incidence of colds is unknown, but it could have to do with the modulation of the immune system. White blood cells, lymphocytes, and neutrophil counts were all increased in both trained and non-trained athletes after sauna use. While these findings are interesting, they're still preliminary and larger studies are needed to confirm. One of the protective adaptive responses to heat stress is the production of heat shock proteins. Heat shock proteins are a conserved class of proteins with critical roles in maintaining cellular homeostasis and in protecting the cells from stressful conditions. Heat shock proteins have been shown to be increased by approximately 50% after 30 minutes in a 163 degree Fahrenheit sauna in healthy young men and women.