Author here. Methodology upfront because I'd ask the same things:
Data: daily records from wearable users who logged sauna sessions via connected apps. Within-person design — each user is their own control, comparing their own sauna-day nights against their own non-sauna-day nights. No cross-user comparisons.
Stats: paired t-tests, FDR-corrected p < 0.05, Cohen's d > 0.2 threshold for "meaningful effect." Anything below d=0.2 we don't report as a finding.
What we measured: minimum nighttime HR, max and average HR, HRV, activity minutes and distance, menstrual cycle phase (for female subset).
What we found:
- On sauna days, minimum nighttime HR drops ~3 bpm (~5%) vs. the same user's non-sauna days.
- Effect survives controlling for activity level. It's not "sauna users just exercised more that day."
- Strongest hypothesis: elevated parasympathetic tone from the post-sauna cooling phase carries into sleep. Consistent with heat-stress physiology literature.
- Sex difference: for women, the nighttime HR effect only crosses the d > 0.2 threshold during the luteal phase. No meaningful effect during the follicular phase. We didn't expect this; worth replicating.
What we can't control for:
- Sauna type (dry / infrared / steam), duration, temperature. Not captured.
- Dose-response. We don't know session length per user.
- Timing of sauna relative to sleep.
- Reverse causation: people may sauna on days they already feel recovered.
- Selection: wearable users who bother logging sauna are a health-conscious cohort.
What surprised us: the effect is larger than what we see for comparable-intensity exercise days. If you treat nighttime HR as a parasympathetic recovery signal, sauna beats a moderate workout on the same user. Not what I'd have predicted.
The most important thing you didn't measure: does this affect long term health in the same way exercise it known to. That is can I put a TV in my sauna and watch that for an hour every day instead of getting out and exercising - yet get the same better long term health outcomes?
My current guess is no. That is this improves a marker for good health without improving health. However this is a guess by someone who isn't in the medical field and so could be wrong.
I recently listened to a podcast about the benefits of sauna or deliberate heat exposure and the gist is that if you get your core temperature at about 39 degrees celsius your cardiovascular system is working comparably hard to light exercise.
My take is that your heart and lungs are working out, even if your body is not. Do you get the same benefits as going for a run or bike ride for a comparable amount of time? no, since your limbs don't get fit, but your heart and lungs do.
Cardiac hypertrophy is not necessarily a bad thing, it can be the result of positive adaptation, such as exercising.
Eccentric hypertrophy (athlete's heart) is the positive adaptation resulting from training the heart. The heart has a lower resting rate and is more efficient at pumping blood. It returns to normal size if training stops.
You'll never reach a state of hypertrophic cardiomyopathy (the bad kind of hypertrophy) with exercise. Its cause is usually genetic.
Not true. You can't really train your muscles to use less oxygen for the same energy output (what "oxygen-efficiency" would imply). You rather increase their capacity to take up oxygen from the blood and burn it. They will use more oxygen to output more energy.
That additional oxygen needs to come from somewhere. Endurance training at the same time trains the heart to deliver more oxygen to the periphery; the primary mechanism is increased cardiac stroke volume.
This is why I hate health science. Informed people can have the same information and come to opposite conclusions. The entire field is made up of contradictory explanations and principles, to the extent that it’s unknowable what’s true or not.
This is terribly uniformed. Do not listen to this.
Cardiac hypertrophy isn't a "bad thing". This is completely contextual. What you don't want, for example, is pathological hypertrophy from things like hypertension, or exclusive left ventricular hypertrophy without associated increase in chamber size.
The heart is very complex. You 100% should exercise it.
This feels like a false dichotomy. Even if sauna doesn't impact long term health in a way that can replace exercise, that doesn't mean that it doesn't improve health.
> That is this improves a marker for good health without improving health
There is a substantial body of existing research to peruse about the impact of regular sauna use on health outcomes, much of it from Finland given the prevalence of sauna usage there allowing for larger sample sizes. It's a body of evidence rather than one knock-out experimental design.
Much of that body of evidence relies on self-reported and self-assigned sauna usage rather than actual randomized trials, and also the papers show massive risk reductions that do not really fit with the country-level data (e.g., if saunas are that good for cardiovascular health and finns use them that much, why do they have similar rates of CV disease as neighboring countries that don't use that much sauna?)
Zero shot you'd make it an hour in a proper sauna for an hour. People have this idea that saunas are always enjoyable. I sauna daily, and its nice up to a point. For me thats like 10-12mins in. From then on, its tough.
When it doesn't feel enjoyable anymore, you're supposed to get out of the sauna and cool down - preferably in a lake. Then repeat as many times as you like.
I generally make it about 30 seconds in a sauna (I rarely even bother trying when I have access). Should I tough it out for 10-12 like you? Should you be toughing it out for the full hour I suggested (a random time I pulled out of my head)? Or is this all nonsense and I'm just fine ignoring the whole thing?
My take is probably too nuanced here, but the reality is that we don't know. People living in areas with longevity (blue zones), didn't really excercise (as in sports) or take multivitamins. For all we know, it might even come out that regular, gym-style excercise is even worse for longevity.
Nordic people tend to live a long life even though they historically didn't have access to fresh vegetables or fruit and brutal winters (and darkness) prohibited excercise.
ps. I'm not arguing that excercise is unhealthy, it's just that its contribution to eventual longevity, is currently unknown. Whereas anectodal evidence of saunas (being around longer than "excercise"), seems to work.
I do wonder what the correlation is: is it only because of excercise, or at least partially also due to the fact those who can set aside time and effort (and often, money) to exercise, have a "better" life than those who don't?
For example, high life expectancy in Madrid, and Switzerland are often attributed to having broad access to great healthcare and stress-free lifestyle(both), despite living a relatively "unhealthy" lifestyle, at least in Madrid. Eating fried food everyday, little exercize among elderly (at least if you don't count walking to the bar). Those 85 year+ Madrileños probably had their last formal exercise when they had to do their military service back in the day.
As in the case of top athletes, in your second article, is their longevity due to heavy exercise, or kind of, "despite it", and at least partially due to their accumulated wealth, health-conscious mindset plus the ability to afford a stress-free life?
> People living in areas with longevity (blue zones), didn't really excercise (as in sports)
Not exercising as in sports and not exercising, period, are very different. If you look at the American blue zone, those people are certainly exercising; daily nature walks are baked into their theology.
Problem is sauna use and genetic factors corrolate too strongly to make any conclusion to the broader population. If you live in/near Finland you likely sauna often, as have all your ancestors for thousands of years. If you don't live there both are false. Thus we can't know if Sauna is helpful for the general population who isn't of a Finish background.
Japan has a +4 years lead of life expectancy over Finland; Norway almost +3 years on Finland. I am not saying this is conclusive per se, but to me the sauna-people-live-forever is not backed up by the data. I would instead reason that, e. g. weight correlates a lot more here.
Nobody is claiming they live forever. The claim is sauna use increases lifespan. There are other factors than just sauna use in lifespan though. The question is would the Japanese live even longer if they were using a sauna?
I looked into Saunas in detail sometime back as a replacement/complement to exercise. There is a lot of research out there which says Saunas are as beneficial - but at the end of it I reached a similar conclusion - exercise is just better understood, so no point experimenting when something can go wrong.
I think that if you have one hour or more of free time and live in an area where you have easy access to a sauna, that would result in significant better health on it's own. Even if you choose to not use the sauna.
That seems like a very strong statement. Isn’t there evidence that Heat Shock Proteins are produced in response to time in the sauna, which have beneficial effects on muscle growth and repair?
How did you control for activity level? Do you have similar BPM plots for the different situations (sauna+exercise, sauna+no exercise, no sauna + exercise, no sauna + no exercise) for a visual representation?
> minimum nighttime HR drops ~3 bpm (~5%)
What wearables were used? These devices don't usually have enough precision to reliably detect ~3bpm changes. Also, the measurements are sensitive to skin, blood flow changes and temperature. How do you know the difference doesn't come from different sensor behavior after sauna?
How would this play out over time? Will sauna see a 3bpm drop below baseline on days it’s used, while keeping the same baseline?
Exercise, over time, should lower the baseline (to a point). I’d think this would have the more desirable long term benefits.
One can do both, of course, but when people see headlines like this they often jump to the conclusion that sauna can replace exercise, because that’s what they want to believe.
Due to lots of long distance running my rest heart rate is below 40. I am highly skeptical I would experience a 3bpm lower heart rate after sauna. Maybe this benefit applies after infrequent activity or less intense activity only.
- Is the wearable accurate enough to be sure that 3bpm is not a measurement fluke?
- Why did you use the minimum heart rate value (which could be a measurement glitch) and did not compare a percentile (e.g., 2.5th lowest percentile)?
- Were all assumptions for paired t-testing valid? How did you account for likely temporal correlations in the data (e.g., sauna could have an effect also on a night 2 days after it, same for exercise)?
- How can you define a "comparable-intensity exercise day" if you don't know the characteristics of the sauna?
> Is the wearable accurate enough to be sure that 3bpm is not a measurement fluke
If the statistical tests show significance (and are valid), the answer to this question is yes. If you have enough data you can make strong conclusions even witwith imperfect hardware.
Just as a discussion point: how do you think these effects would translate (if at all) to regularly practicing hot yoga, say around 100-105F? Intuitively, it would combine the effort + recovery, but probably not enough time elapsed in the same session for the sweat benefit during muscle repair?
I'm equally confused as the other person above. Why not just ask participants to report what type of sauna they used? Sure humidity/duration/temp would be awesome to have, but at the very minimum knowing if a dry sauna would get the same results as a traditional steam sauna.
> Motivated to understand the immediate physiological response to saunas, we looked at the same-day effects across ~59,000 daily records from 256 users.
Anecdotal, of course, but the biggest change I ever made in my life was right before bed: take a screaming hot shower with dim lighting. I'd say 95% of the time, I get in bed and just pass out and have no real memory of time passing before falling asleep.
Increasing skin temperature is known to induce sleep (can't find a source currently, sorry). Something about your skin being warmer allowing your body to cool more effectively, I think.
So a hot shower before bed is actually great for sleep, because you get the increased skin temp, relaxed muscles from the warm water, and general relaxation because showers are (for many people) relaxing.
I know that for myself exercise increases my resting heart rate in the short term. It only decreases after a day or two, sometimes more depending on how fatigued I am.
I thought that was common, with recovery times obviously decreasing the fitter ones gets.
n= traditionally refers to the number of participants, not the number of data points.
The headline claim is very misleading for anyone who thought there were 59,000 people in this data set.
The absolute difference is also small. Small enough that the effect might be attributable to something secondary, such as sauna users consuming more water in recovery and being more hydrated. Heart rate has a relationship with hydration status.
Not to be glib, but being dead lowers your night time heart rate more then exercise as well.
Is having a lower night time heart rate the core goal of exercise? Is it even a goal at all? Or is it just an indicator of other goals being reached? I'm genuinely curious, I wasn't aware that the number mattered, more than what that number actually represents.
N=1, but I started rowing (indoor, on an erg) an hour a day -- not hard, generally 120-140 bpm -- every day starting February 28, after rowing inconsistently for a year or more before that. My resting (not sleep) pulse has dropped by 10% over the past ~7 weeks, from 60 to 54.
Seems to me what we now know about neural networks, we should maybe weighted sum of inputs, that fire off the desired output. The human body/brain process all kinds of stimulus at once, and might only react to a combination of inputs.
Sumo wrestlers in Japan have a life expectancy
between 60-65 years or so - significantly lower than
the other japanese.
I am not saying that sauna has no positive effect
at all, but I would reason that the number one risk
factor is ... weight. And I'd also still say that
exercise is correlated here, if only secondary, e. g.
you may be able to maintain better bodily functions
if you exercise, if you can avoid injury. I do not
think that going into the sauna rather than e. g.
light running for 5 to 10 minutes or so, is anywhere
near on the same level.
"Saunas are a hot, dry environment used to stimulate our cardiovascular system."
That does not sound like a sauna to me. A sauna involves something heating up rocks, and then water being poured upon those rocks - which of course immediately becomes steam.
All of which means that a sauna is humid, and not at all dry. That's why, here in Finland, saunas are considered wet-spaces. Complete with floor drain - though i grant you that is also used for scrubbing them down and cleanup now and again.
Some people have boxes with infra-red heaters, and they pretend they are saunas, but they absolutely are not. They're a different thing, though I don't know what the point of them is.
> In a typical Finnish sauna, the temperature of the air, the room, and the benches are above the dew point even when water is thrown on the hot stones and vaporized. Thus, they remain dry. In contrast, the sauna bathers are at about 60–80 °C (140–176 °F), which is below the dew point, so that water is condensed on the bathers' skin. This process releases heat and makes the steam feel hot.
I mean yes it depends on your definition of humid but if your definition of humid is under 20% RH then that's not in agreement with any other humans on the planet and if it's over 50% RH then no, millions of people are not doing this because they would die. Our bedroom is at 50% RH because under that our baby's skin dries out. There's no way anyone is sitting in a 90 C 50% RH sauna for any appreciable amount of time. They would die.
Haha no, I been in 90c saunas many times. Can I stay there for a long time? Heck no. But some people can and it doesn’t kill you (maybe if you have some preexisting condition)
No, it seems saunas have very low relative humidity except for briefly after you splash the hot rocks. "Relative" is the key term there: the absolute humidity is high, but the hot air can accept much more H20 and it will suck moisture off your body. So it is a dry environment according to humans.
Yeah, I’ve taken hundreds of (Finnish) saunas (both electric and woodfired) and they all have one thing in common: they’re dry. It’s a bit more humid when you throw water on the rocks, but it generally stays between 10-40% RH. This is a good thing, as 90% RH at 90C would be uncomfortable to say the least.
I can tell you wrote the article with ChatGPT. I’m out as soon as I pick up the smell. I don’t dislike the usage of AI, I just don’t trust. It if you haven’t written it yourself.
I feel like we need an acronym for this kind of comment. I am pretty sure approximately 100% of HN posts now include at least one comment where someone, somehow, knows that an article is written by AI and resents it.
For Claude we have the ever present "you are absolutely right" and this is like it's human mirror.
Something like TLDR; but meaning "uhg, written by AI".
Author here. Methodology upfront because I'd ask the same things:
Data: daily records from wearable users who logged sauna sessions via connected apps. Within-person design — each user is their own control, comparing their own sauna-day nights against their own non-sauna-day nights. No cross-user comparisons.
Stats: paired t-tests, FDR-corrected p < 0.05, Cohen's d > 0.2 threshold for "meaningful effect." Anything below d=0.2 we don't report as a finding.
What we measured: minimum nighttime HR, max and average HR, HRV, activity minutes and distance, menstrual cycle phase (for female subset).
What we found: - On sauna days, minimum nighttime HR drops ~3 bpm (~5%) vs. the same user's non-sauna days. - Effect survives controlling for activity level. It's not "sauna users just exercised more that day." - Strongest hypothesis: elevated parasympathetic tone from the post-sauna cooling phase carries into sleep. Consistent with heat-stress physiology literature. - Sex difference: for women, the nighttime HR effect only crosses the d > 0.2 threshold during the luteal phase. No meaningful effect during the follicular phase. We didn't expect this; worth replicating.
What we can't control for: - Sauna type (dry / infrared / steam), duration, temperature. Not captured. - Dose-response. We don't know session length per user. - Timing of sauna relative to sleep. - Reverse causation: people may sauna on days they already feel recovered. - Selection: wearable users who bother logging sauna are a health-conscious cohort.
What surprised us: the effect is larger than what we see for comparable-intensity exercise days. If you treat nighttime HR as a parasympathetic recovery signal, sauna beats a moderate workout on the same user. Not what I'd have predicted.
The most important thing you didn't measure: does this affect long term health in the same way exercise it known to. That is can I put a TV in my sauna and watch that for an hour every day instead of getting out and exercising - yet get the same better long term health outcomes?
My current guess is no. That is this improves a marker for good health without improving health. However this is a guess by someone who isn't in the medical field and so could be wrong.
I recently listened to a podcast about the benefits of sauna or deliberate heat exposure and the gist is that if you get your core temperature at about 39 degrees celsius your cardiovascular system is working comparably hard to light exercise.
My take is that your heart and lungs are working out, even if your body is not. Do you get the same benefits as going for a run or bike ride for a comparable amount of time? no, since your limbs don't get fit, but your heart and lungs do.
You don't want to "work out" your heart though. Cardiac hypertrophy is a bad thing.
The benefit of exercise is that your muscles become more oxygen-efficient. Your heart endures some stress now, so that it can work less in the future.
Cardiac hypertrophy is not necessarily a bad thing, it can be the result of positive adaptation, such as exercising.
Eccentric hypertrophy (athlete's heart) is the positive adaptation resulting from training the heart. The heart has a lower resting rate and is more efficient at pumping blood. It returns to normal size if training stops.
You'll never reach a state of hypertrophic cardiomyopathy (the bad kind of hypertrophy) with exercise. Its cause is usually genetic.
Not true. You can't really train your muscles to use less oxygen for the same energy output (what "oxygen-efficiency" would imply). You rather increase their capacity to take up oxygen from the blood and burn it. They will use more oxygen to output more energy.
That additional oxygen needs to come from somewhere. Endurance training at the same time trains the heart to deliver more oxygen to the periphery; the primary mechanism is increased cardiac stroke volume.
This is why I hate health science. Informed people can have the same information and come to opposite conclusions. The entire field is made up of contradictory explanations and principles, to the extent that it’s unknowable what’s true or not.
Wikipedia says Athlete's heart is benign: https://en.wikipedia.org/wiki/Athletic_heart_syndrome
This is terribly uniformed. Do not listen to this.
Cardiac hypertrophy isn't a "bad thing". This is completely contextual. What you don't want, for example, is pathological hypertrophy from things like hypertension, or exclusive left ventricular hypertrophy without associated increase in chamber size.
The heart is very complex. You 100% should exercise it.
That seems… misguided.
Sources?
Your heart is also a muscle.
Agreed - one is muscular/metabolic demand, the other (sauna) is thermoregulation.
Agreed on the long-term effect too: doing a study on long term health is a completely different story
This feels like a false dichotomy. Even if sauna doesn't impact long term health in a way that can replace exercise, that doesn't mean that it doesn't improve health.
> That is this improves a marker for good health without improving health
There is a substantial body of existing research to peruse about the impact of regular sauna use on health outcomes, much of it from Finland given the prevalence of sauna usage there allowing for larger sample sizes. It's a body of evidence rather than one knock-out experimental design.
Much of that body of evidence relies on self-reported and self-assigned sauna usage rather than actual randomized trials, and also the papers show massive risk reductions that do not really fit with the country-level data (e.g., if saunas are that good for cardiovascular health and finns use them that much, why do they have similar rates of CV disease as neighboring countries that don't use that much sauna?)
Zero shot you'd make it an hour in a proper sauna for an hour. People have this idea that saunas are always enjoyable. I sauna daily, and its nice up to a point. For me thats like 10-12mins in. From then on, its tough.
When it doesn't feel enjoyable anymore, you're supposed to get out of the sauna and cool down - preferably in a lake. Then repeat as many times as you like.
I go for 15 min sessions at 90 Celsius and the first 10 mins are ok, the last 5 are tough, like I have to control my breath to hang in there
I generally make it about 30 seconds in a sauna (I rarely even bother trying when I have access). Should I tough it out for 10-12 like you? Should you be toughing it out for the full hour I suggested (a random time I pulled out of my head)? Or is this all nonsense and I'm just fine ignoring the whole thing?
You are clearly not Finn (/s)
My take is probably too nuanced here, but the reality is that we don't know. People living in areas with longevity (blue zones), didn't really excercise (as in sports) or take multivitamins. For all we know, it might even come out that regular, gym-style excercise is even worse for longevity.
Nordic people tend to live a long life even though they historically didn't have access to fresh vegetables or fruit and brutal winters (and darkness) prohibited excercise.
ps. I'm not arguing that excercise is unhealthy, it's just that its contribution to eventual longevity, is currently unknown. Whereas anectodal evidence of saunas (being around longer than "excercise"), seems to work.
> I'm not arguing that excercise is unhealthy, it's just that its contribution to eventual longevity, is currently unknown
I see numerous studies indicating that exercise contributes directly to eventual longevity, e.g.:
https://www.ama-assn.org/public-health/prevention-wellness/m...
https://www.acc.org/latest-in-cardiology/articles/2025/07/02...
https://pmc.ncbi.nlm.nih.gov/articles/PMC3395188/
Thank you for the resources.
I do wonder what the correlation is: is it only because of excercise, or at least partially also due to the fact those who can set aside time and effort (and often, money) to exercise, have a "better" life than those who don't?
For example, high life expectancy in Madrid, and Switzerland are often attributed to having broad access to great healthcare and stress-free lifestyle(both), despite living a relatively "unhealthy" lifestyle, at least in Madrid. Eating fried food everyday, little exercize among elderly (at least if you don't count walking to the bar). Those 85 year+ Madrileños probably had their last formal exercise when they had to do their military service back in the day.
As in the case of top athletes, in your second article, is their longevity due to heavy exercise, or kind of, "despite it", and at least partially due to their accumulated wealth, health-conscious mindset plus the ability to afford a stress-free life?
There is some evidence suggesting that "blue zones" are largely about pension fraud. https://fortune.com/europe/2024/12/14/are-blue-zones-myth-ex...
You're saying that crime leads to longevity? Big if true.
> People living in areas with longevity (blue zones), didn't really excercise (as in sports)
Not exercising as in sports and not exercising, period, are very different. If you look at the American blue zone, those people are certainly exercising; daily nature walks are baked into their theology.
For all we know, there is a link between cardiac/circulatory problems and arteriosclerosis (that is, loss of elasticity of the vessels).
So it could be that exercise helps keep this elasticity, the same way maybe sauna does? Also antioxidants from vegetables etc.
So it could be that it is a _factor_, but definitely needs way more study.
I am also not in the medical field, but I think arteriosclerosis is a well known link for cardiovascular disease.
The "blue-zone" studies are flawed, so we shouldn't infer too much from lifestyle generalizations about people in them.
https://www.science.org/content/article/do-blue-zones-suppos...
Problem is sauna use and genetic factors corrolate too strongly to make any conclusion to the broader population. If you live in/near Finland you likely sauna often, as have all your ancestors for thousands of years. If you don't live there both are false. Thus we can't know if Sauna is helpful for the general population who isn't of a Finish background.
Japan has a +4 years lead of life expectancy over Finland; Norway almost +3 years on Finland. I am not saying this is conclusive per se, but to me the sauna-people-live-forever is not backed up by the data. I would instead reason that, e. g. weight correlates a lot more here.
Nobody is claiming they live forever. The claim is sauna use increases lifespan. There are other factors than just sauna use in lifespan though. The question is would the Japanese live even longer if they were using a sauna?
A lot of Mediterranean countries also have high life expectancy and are the opposite of a sauna culture.
Cyprus summers are like 45C and its almost like a sauna :)
Maybe eating a lot of fish, rather than meat, has an impact too.
I looked into Saunas in detail sometime back as a replacement/complement to exercise. There is a lot of research out there which says Saunas are as beneficial - but at the end of it I reached a similar conclusion - exercise is just better understood, so no point experimenting when something can go wrong.
I think that if you have one hour or more of free time and live in an area where you have easy access to a sauna, that would result in significant better health on it's own. Even if you choose to not use the sauna.
One hour in sauna? :O
A random time I pulled out of my head. If this is real the next question is what is the optimal time. (also temperature and humidity levels)
A sauna will do nothing for muscular-skeletal health.
That seems like a very strong statement. Isn’t there evidence that Heat Shock Proteins are produced in response to time in the sauna, which have beneficial effects on muscle growth and repair?
I don’t think the TV in the sauna will have long term health outcomes.
It will certainly affect the health of the TV.
I'd like to see a bit more detailed methods.
- How was the controlling for the other factors done? A linear model?
- What were the sauna vs non-sauna baseline HRs in fig 1? Could you plot raw averages?
- Was the min HR explicitly computed during the night (in Fig 2), or was it assumed min HR occurs during the night?
- Reporting only significant results is not prudent even with multiple comparisons corrections, please report all tests made
> Effect survives controlling for activity level.
How did you control for activity level? Do you have similar BPM plots for the different situations (sauna+exercise, sauna+no exercise, no sauna + exercise, no sauna + no exercise) for a visual representation?
> minimum nighttime HR drops ~3 bpm (~5%)
What wearables were used? These devices don't usually have enough precision to reliably detect ~3bpm changes. Also, the measurements are sensitive to skin, blood flow changes and temperature. How do you know the difference doesn't come from different sensor behavior after sauna?
> What wearables were used? These devices don't usually have enough precision to reliably detect ~3bpm changes.
For large sample averages this doesn't really matter.
How would this play out over time? Will sauna see a 3bpm drop below baseline on days it’s used, while keeping the same baseline?
Exercise, over time, should lower the baseline (to a point). I’d think this would have the more desirable long term benefits.
One can do both, of course, but when people see headlines like this they often jump to the conclusion that sauna can replace exercise, because that’s what they want to believe.
Due to lots of long distance running my rest heart rate is below 40. I am highly skeptical I would experience a 3bpm lower heart rate after sauna. Maybe this benefit applies after infrequent activity or less intense activity only.
If this was a peer-reviewed paper, it won't pass.
- Is the wearable accurate enough to be sure that 3bpm is not a measurement fluke? - Why did you use the minimum heart rate value (which could be a measurement glitch) and did not compare a percentile (e.g., 2.5th lowest percentile)? - Were all assumptions for paired t-testing valid? How did you account for likely temporal correlations in the data (e.g., sauna could have an effect also on a night 2 days after it, same for exercise)? - How can you define a "comparable-intensity exercise day" if you don't know the characteristics of the sauna?
> Is the wearable accurate enough to be sure that 3bpm is not a measurement fluke
If the statistical tests show significance (and are valid), the answer to this question is yes. If you have enough data you can make strong conclusions even witwith imperfect hardware.
Unless the effect they're measuring is that the wearable measures differently in sauna days.
Strong conclusion that the hardware is precisely imperfect?
Just as a discussion point: how do you think these effects would translate (if at all) to regularly practicing hot yoga, say around 100-105F? Intuitively, it would combine the effort + recovery, but probably not enough time elapsed in the same session for the sweat benefit during muscle repair?
Or the sauna is a relaxing thing like a happy place and that reduces heart rate?
It would be very interesting if lowering night heart rate only happens with certain sauna type.
> What we can't control for: - Sauna type (dry / infrared / steam), duration, temperature. Not captured
Could probably capture humidity/duration/temperature using a sensor in wearable device...
we agree - but thats not that simple :)
> who logged sauna sessions via connected apps
It seems you ask participants to log if they went to sauna. Out of curiosity, why is it not simple to also ask for a type?
i was mostly refering to humidity/duration/temperature given that most devices do not report back these values
I'm equally confused as the other person above. Why not just ask participants to report what type of sauna they used? Sure humidity/duration/temp would be awesome to have, but at the very minimum knowing if a dry sauna would get the same results as a traditional steam sauna.
Why didn't you put the methodology in the post? Also, which devices were used to record? How do you know people went to sauna?
how does this reduction in heartbeat at night affect the body?
> Motivated to understand the immediate physiological response to saunas, we looked at the same-day effects across ~59,000 daily records from 256 users.
Editorialized title is wrong. n=256
Fair flag: 256 users, 59k days
Anecdotal, of course, but the biggest change I ever made in my life was right before bed: take a screaming hot shower with dim lighting. I'd say 95% of the time, I get in bed and just pass out and have no real memory of time passing before falling asleep.
Increasing skin temperature is known to induce sleep (can't find a source currently, sorry). Something about your skin being warmer allowing your body to cool more effectively, I think.
So a hot shower before bed is actually great for sleep, because you get the increased skin temp, relaxed muscles from the warm water, and general relaxation because showers are (for many people) relaxing.
I know that for myself exercise increases my resting heart rate in the short term. It only decreases after a day or two, sometimes more depending on how fatigued I am. I thought that was common, with recovery times obviously decreasing the fitter ones gets.
n= traditionally refers to the number of participants, not the number of data points.
The headline claim is very misleading for anyone who thought there were 59,000 people in this data set.
The absolute difference is also small. Small enough that the effect might be attributable to something secondary, such as sauna users consuming more water in recovery and being more hydrated. Heart rate has a relationship with hydration status.
Not to be glib, but being dead lowers your night time heart rate more then exercise as well.
Is having a lower night time heart rate the core goal of exercise? Is it even a goal at all? Or is it just an indicator of other goals being reached? I'm genuinely curious, I wasn't aware that the number mattered, more than what that number actually represents.
It's just another measure. It's not ceteris paribus better to have a lower one.
From the author, "Strongest hypothesis: elevated parasympathetic tone from the post-sauna cooling phase carries into sleep"
AKA, they use it as a proxy to infer a deeper state of rest and improved recovery state. Says nothing about the fatigue generated from using a sauna.
N=1, but I started rowing (indoor, on an erg) an hour a day -- not hard, generally 120-140 bpm -- every day starting February 28, after rowing inconsistently for a year or more before that. My resting (not sleep) pulse has dropped by 10% over the past ~7 weeks, from 60 to 54.
Seems to me what we now know about neural networks, we should maybe weighted sum of inputs, that fire off the desired output. The human body/brain process all kinds of stimulus at once, and might only react to a combination of inputs.
N=256
Well ...
Finland life expectancy for 2023 was 81.69.
Norway life expectancy for 2025 was 83.23.
Japan life expectancy for 2025 was 85.27.
Sumo wrestlers in Japan have a life expectancy between 60-65 years or so - significantly lower than the other japanese.
I am not saying that sauna has no positive effect at all, but I would reason that the number one risk factor is ... weight. And I'd also still say that exercise is correlated here, if only secondary, e. g. you may be able to maintain better bodily functions if you exercise, if you can avoid injury. I do not think that going into the sauna rather than e. g. light running for 5 to 10 minutes or so, is anywhere near on the same level.
Website doesn’t load, it times out. Anyone have tl;dr?
it works for me - what browser are you using?
The fine article says:
"Saunas are a hot, dry environment used to stimulate our cardiovascular system."
That does not sound like a sauna to me. A sauna involves something heating up rocks, and then water being poured upon those rocks - which of course immediately becomes steam.
All of which means that a sauna is humid, and not at all dry. That's why, here in Finland, saunas are considered wet-spaces. Complete with floor drain - though i grant you that is also used for scrubbing them down and cleanup now and again.
Some people have boxes with infra-red heaters, and they pretend they are saunas, but they absolutely are not. They're a different thing, though I don't know what the point of them is.
Downvotes have spoken though.
https://en.wikipedia.org/wiki/Sauna#Modern_saunas
> In a typical Finnish sauna, the temperature of the air, the room, and the benches are above the dew point even when water is thrown on the hot stones and vaporized. Thus, they remain dry. In contrast, the sauna bathers are at about 60–80 °C (140–176 °F), which is below the dew point, so that water is condensed on the bathers' skin. This process releases heat and makes the steam feel hot.
This just means the surfaces are dry. The commenter said the air is not dry.
Putting water on hot stones in a sauna does not raise the humidity nearly as much as you think it does.
Sounds like it doesn't have to be wet to be a sauna.
> A sauna is a room or building designed as a place to experience dry or wet heat sessions or an establishment with one or more of these facilities.
https://en.wikipedia.org/wiki/Sauna
There are different kinds of saunas. Nobody gets into a 90c humid sauna, that would just kill you.
Oh I can assure you, millions people in the northern europe do exactly this ;)
EDIT: I guess it depends on your definition of "humid". But 90C and regular water infusions are pretty common sauna conditions.
I mean yes it depends on your definition of humid but if your definition of humid is under 20% RH then that's not in agreement with any other humans on the planet and if it's over 50% RH then no, millions of people are not doing this because they would die. Our bedroom is at 50% RH because under that our baby's skin dries out. There's no way anyone is sitting in a 90 C 50% RH sauna for any appreciable amount of time. They would die.
I guess I am a revenant - I get into one regularly in my basement.
Haha no, I been in 90c saunas many times. Can I stay there for a long time? Heck no. But some people can and it doesn’t kill you (maybe if you have some preexisting condition)
the point is the humidity. hot saunas need to be relatively dry otherwise your sweat won't evaporate.
No, it seems saunas have very low relative humidity except for briefly after you splash the hot rocks. "Relative" is the key term there: the absolute humidity is high, but the hot air can accept much more H20 and it will suck moisture off your body. So it is a dry environment according to humans.
According to this company plus some sketchy math I just did, the relative humidity can swing between 15% and 40%: all over the place, but generally pretty dry. https://www.vaisala.com/en/blog/2024-12/can-you-handle-heat-...
Yeah, I’ve taken hundreds of (Finnish) saunas (both electric and woodfired) and they all have one thing in common: they’re dry. It’s a bit more humid when you throw water on the rocks, but it generally stays between 10-40% RH. This is a good thing, as 90% RH at 90C would be uncomfortable to say the least.
I can tell you wrote the article with ChatGPT. I’m out as soon as I pick up the smell. I don’t dislike the usage of AI, I just don’t trust. It if you haven’t written it yourself.
I feel like we need an acronym for this kind of comment. I am pretty sure approximately 100% of HN posts now include at least one comment where someone, somehow, knows that an article is written by AI and resents it.
For Claude we have the ever present "you are absolutely right" and this is like it's human mirror.
Something like TLDR; but meaning "uhg, written by AI".
This article is a brilliant skewering of the 'em dash means LLM' heuristic as a broken trick deployed by those too-clever-by-half.
1. https://www.scottsmitelli.com/articles/em-dash-tool/
Thank you for this. This is like finding a book where someone has written down what I've been thinking, but better than I ever could.