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.
Since you mention the TV, it seems there's a big factor missing in both the article and the discussion here. Namely, that sauna time is for many people the only time they ever take to be in silence, without the countless distractions otherwise bombarding our nervous systems. I.e. it's basically a form of informal meditation, which is known to have a lot of benefic impacts on body and mind. So maybe skip the TV part?...
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.
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.
This question is dead from the beginning. Exercise is good for the heart, the muscles, metabolism. You do need muscle contractions above certain level of intensity and duration for this to happen.
My current guess is that you get much or most of the benefits, but not all (by both value and number). If you look at the actual changes in the body during both of these activities, most are the same as exercise, but not all.
For example: body temp increases, heart rate increases, and we sweat. But the muscles aren't "engaged", consuming stuff (glycogen, etc.) while doing sauna.
There could also be sauna benefits that exercise does not impart, or is less likely to do so: sweating greater than exercise could lead to excess excretion of plastics, carcinogens, etc.
Running in mild/cold temps we do little sweating (unless long duration exercise), whereas every darn sauna at sufficiently high temps we are going to be sweating.
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 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.
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'm being slightly snarky, but good luck watching a TV if you're doing an intense/valuable sauna session.
When I'm in my dry sauna and really pushing myself with the heat and steam off the hot rocks, I basically have to mediate to stay in beyond 15 minutes because every part of my mind starts telling me to get out and cool down.
Even more likely is those using saunas and tracking metrics with wearables are self-selected to be healthier/more active/etc. Correlation and causation...
From the article:
"..promotes sweating and therefore the elimination of toxins,.."
That false statement really makes me unsure about the quality of the article. And I'm saying this as someone who uses sauna daily, when possible (I have one at home, and I grew up with saunas).
"De-toxification" by sweating is a myth. Sweat glands are very simple organs (think salt on one side, which results in pressure, i.e. osmosis) and can't do anything of the sort. You'll be much better off peeing.
Saunas probably have good health effects. I'm certainly happy as a sauna user. But there's no de-toxification in this.
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?
- 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.
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.
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?
As someone with access to both Japanese ofuro and sauna, they are quite different in some respects. And similar in others. One thing which a sauna could do for me when the ofuro could not, was to fix a problem I had with coughing. Something which plauged me for a long time, and which the doctors couldn't find any reason for, but I had such painful daily coughs that it really bothered me. Couldn't sleep on my back either. Then I noticed that if I used the sauna daily, and carefully breathed hot air, the symptoms lessened. And after going for the daily sauna regime (instead of occasionally) for some time, the coughing problem I had for years finally disappeared. The hot baths did nothing for this (but was good for other things, e.g. muscle pains. And essential for being able to sleep at cold winter nights in non-insulated Japanese homes.. heating up the body with a very long very hot bath does wonders)
A lot of people go to sauna after workout. I rarely go to sauna without workout so not sure if the combination is helping me or exercise or the sauna. How to control for that?
Just because your heart rate is lower does it mean you’re any healthier however. This is just ridiculous measurement it means nothing.
The sauna might be acting like any other drug. There are a lot of drugs that will lower nighttime heart rate. Does that mean those drugs are healthier for you?
If your resting heart rate is lower without any drugs, it indicates that your heart can cause sufficient oxygen to be delivered to your organs with less effort than if it were higher. That can be caused by a variety of things (including stroke volume, capillary dilation and general obstruction (or not) of blood vessels). These are all good proxies for general health.
Drugs lowering your resting heart rate do not indicate this in the same way.
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.
That's funny, I find it much easier to fall asleep in a cold environment. Then again, I also like to use a heavy blanket, so maybe it's the weight more than the cold that's helping me.
Hot shower heats up your body, which causes it to direct blood away from the core to cool it down so it doesn't overheat. Dropping core temp triggers the brain to ramp up melatonin production. Or so I heard.
Conversely, when the temperature drops, your body directs blood away from your hands and legs because core has higher priority for survival
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.
A delta of 3 bpm on sauna days corresponds to around 4% delta if the baseline is 72 bpm. I've gone from a resting heart rate over a 7-day average of 64 bpm to 58 bpm by jumping 15 min. of rope a day, 4 times a week. I've lost weight, body fat, and I feel like my body is more efficient with corresponding lower heart rates throughout my active day. I like saunas for recovery and aches, they put me in a relaxed state after, and I believe the dilation is flushing my system. Like anything else, moderation. Perhaps I will add sauna to my weekly routine 1x per week or less.
PSA: if you like saunas but don't have easy access to one, those IR sauna bags you can buy online work great.
Some people find it gross to basically sweat inside a powered sleeping bag, but if you don't mind that you can get the same effects of a sauna while lying on your (covered) couch and watching YouTube.
Wow, they look really quite dangerous. I wouldn’t want to pass out in one. Yeah you can pass out in a sauna too, but it feels easier to lurch for the door than to fight with a sleeping bag.
TLDR: regular sauna seems to have no effect on my resting HR. Extended high HR cardio definitely does.
I became a huge fan of sauna time (15-20 minutes at approx 175F/80C... I would prefer a bit warmer, but I had no control). It was like shower time, or meditation time (which I never took time for). Great thinking time. I'd use it after a workout, but I would also use it on days without a workout.
I've been tracking some stats via my Garmin watch for a few years, and I've identified some patterns - particularly regarding resting HR.
The most significant reducer of resting heart rate for me is running (5k). Periods where my training includes regular 5k runs cause my resting HR to drop by 5-8 bpm.
Most of my training is resistance, although in the last 6 months I've added in a lot more cardio. Stairs and rowing do not seem to noticeably reduce my resting HR. Running definitely does. But to be fair, maybe it's not the running but rather the active HR I'm sustaining. Despite trying to stay in the aerobic zone, running always pushes me to zones 4 and 5. So 50% of my 30 minutes of exercise will be in my max zone. With stairs or rowing, I can keep my HR in aerobic and threshold.
Some stats:
When I'm off my fitness routine, living life as a typical person, my resting HR is 65. When I'm on a resistance fitness routine, my resting HR is 58. When I'm also running, the rHR is 51.
If I eat a heavy meal too close to bedtime, my rHR is +15. If I drink a lot of alcohol before sleeping, rHR can be +20! Food + alcohol = WTF. Probably not good.
Can anyone suggest why after covid I can't do Finnish sauna anymore? Prior to that I used to do 1-2x a week a sequence of 5x(10 minutes in sauna + 5 minutes cold water immersion + 10 minutes rest) which was absolutely great for both stress reduction and blood flow. Now if I do 5 minutes in sauna I feel like my skin was burning and I am about to die, and I need to recover for 1 hour from that to be able to just walk away from sauna.
I'm a big fan of soaking in hot water and have noticed that cardiac function seems to have a massive effect on heat tolerance as measured vs body temperature.
For example, if I've been totally sedentary for the whole day (and my feet are chilly+blue), a body temperature as low as 101F is unbearable. But if I've been actively moving around all day (and my feet are warm and pink), I only start getting uncomfortable at a body temperature around 103.5F-104F.
This also seems to correlate over a longer timespan re: exercise habits, consumption habits, sickness, etc.
Shot in the dark, but has your actual stove changed? When have you last changed the stones? Is the circulation of air worse?
If your skin feels hot my guess would be that the steaming effect might be disrupted by the water getting evaporated faster than before, and the circulation of air also affects the skin feel (that’s why a certain seating position can make sauna unbearable). You could also try to just turn it on at the lowest setting and see if it changes anything. Maybe the stones have gotten so old that old heat settings have sneakily turned unbearable.
Did it happen suddenly? Or did you go for a long time without using a sauna, and noticed the change only when you resumed? Did anything else about your body change, such as weight loss (perhaps from a GLP-1)?
It's possible that Covid had nothing to do with it, and your body is simply changing with age. It's depressing, but it happens!
Once in a while as I get sick I have to retrain myself to going to sauna (e.g. taking lowest level, even skipping the Aufguss, German infusion where temperature is raised gradually etc.)
Also IMO your body fat/water/lean muscle ratio may play a role. I once lost 5 kg due to Influenza A and all my sport achievements as well as sauna endurance were gone
anecdotal -but- it took me 6 months after covid for my breathing rate to go back to normal, and to be able to do consistent max our efforts of >190BPM for >5 seconds like previously
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.
This would not pass peer review for a journal as written.
Maybe the conclusion is correct, or maybe not, but as written the methodology is under specified, statistics are not supported, and there too many confounders not addressed. One should not take anything from this without a better write up. Just misunderstanding what n= means is a huge flag.
Since the author is here, I have to ask: Why a blog post and not an actual paper? Why spray this onto the internet without validating the work? Or, conversely, why not caveat the work as exploratory data science?
I try to do 180 minutes a week of cardio. Mostly Zone 2. Biking, elliptical, tKD. But once in a while my legs feel too tired, so I complete my weekly minutes going to the steam room. It makes sense to me since it raises your heart rate.
Also, my samsung watch can measure stress (whatever it means). It always shows the very, very minimal stress for me. The only time that I have been stressed was the day that I spent a bit too much on the steam room.
FWIW, most of the studies on improvements in blood plasma volume from passive heat are usually done on saunas with temperatures > 150 degrees F (60 C). Steam rooms usually only get up to 120F (~49C) even though the humidity probably makes it feel warmer.
This is contested by a significant number of contemporary running coaches (see, for example "Training for Uphill Athletes" by Steve Johnson or any of the life work of Phil Maffetone.
HIIT is quite effective at something; it's not clear that it is effective at all possible exercise goals (including, but not limited to, endurance running).
Johnson in particular says that unless you've already narrowed the gap between your "first" and "second" (anaerobic) threshold to 5%, HIIT really doesn't make much sense because you're "aerobically challenged" and need to work on that first, which he believes (with significant evidence) is best done almost entirely in zone 2.
He also notes that someone like Eliud Kipchoge can spend 2 hours running 4:30 min/mile pace, so that is clearly within his aerobic range, but that Kipchoge would never and should never spend much time training at that pace because of the load it would put on his system. So the zones that are used for training purposes depend significantly on the current fitness level of the athlete.
I have used HIIT effectively to get myself out of certain fitness/training "ruts", but I think that the zone 2 folks have somevery cogent and coherent observations and advice.
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.
No, immediately lowering heart rate isn't a goal of exercise. The reason it's a meaningful measure at all is because a lower resting heart rate, not overnight in response to a stimulus, but a permanently lower resting heart rate, is a sign that your overall cardiorespiratory system has become more efficient in terms of how much blood it can deliver per beat, how much oxygen it can deliver per unit of blood, and how much energy can be generated per unit of oxygen in your mitochondria. When those efficiencies improve, fewer beats per minute results in the same level of work done in your cells. Thus, resting heart acts as a proxy measure of aerobic fitness, not a goal in and of itself. All of those are long-term adaptations. Conversely, there are many ways to acutely lower heart rate that are clearly not healthy. Death, obviously, but taking opioids or many other kinds of depressants, not moving ever, sleeping 23 hours a day, will all lower your average heart rate immediately without making you fitter or healthier.
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.
General advice: citing absolute HR numbers is pretty meaningless for a broad audience, because they are not intepretable. Express them as percentages of your current max HR to be meaningful to others.
Potentially, but likely much less effective and less studied, and you likely need longer sessions for effective dosage.
Most of the studies I've seen on improvements in blood plasma volume from passive heat are usually done with sessions in saunas with temperatures > 150 degrees F (60 C). Steam rooms usually only get up to 120F (~49C) even though the humidity probably makes it feel warmer.
Copying and pasting some of my reply to another comment above
Sweating is one the main triggers for an increase in blood plasma volume, and the humidity level of a steam room causes vastly higher rates of sweating than most saunas do. You can lose significant body heat by sweating in a dry environment, but much less in high humidity. Consequently, your body needs to sweat much more rapidly even though the absolute temperature may be lower.
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.
Its a cloudflare gateway timeout, so not working for anyone on any browser right now. Seems like a contradiction if cloudflare cant cache what is presumably a static site.
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.
> Motivated to understand the immediate physiological response to saunas, we looked at the same-day effects across ~59,000 daily records from 256 users.
> 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.
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.
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Since you mention the TV, it seems there's a big factor missing in both the article and the discussion here. Namely, that sauna time is for many people the only time they ever take to be in silence, without the countless distractions otherwise bombarding our nervous systems. I.e. it's basically a form of informal meditation, which is known to have a lot of benefic impacts on body and mind. So maybe skip the TV part?...
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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.
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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.
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This question is dead from the beginning. Exercise is good for the heart, the muscles, metabolism. You do need muscle contractions above certain level of intensity and duration for this to happen.
My current guess is that you get much or most of the benefits, but not all (by both value and number). If you look at the actual changes in the body during both of these activities, most are the same as exercise, but not all.
For example: body temp increases, heart rate increases, and we sweat. But the muscles aren't "engaged", consuming stuff (glycogen, etc.) while doing sauna.
There could also be sauna benefits that exercise does not impart, or is less likely to do so: sweating greater than exercise could lead to excess excretion of plastics, carcinogens, etc.
Running in mild/cold temps we do little sweating (unless long duration exercise), whereas every darn sauna at sufficiently high temps we are going to be sweating.
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.
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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.
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.
A sauna will do nothing for muscular-skeletal health.
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I'm being slightly snarky, but good luck watching a TV if you're doing an intense/valuable sauna session.
When I'm in my dry sauna and really pushing myself with the heat and steam off the hot rocks, I basically have to mediate to stay in beyond 15 minutes because every part of my mind starts telling me to get out and cool down.
I don’t think the TV in the sauna will have long term health outcomes.
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One hour in sauna? :O
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Even more likely is those using saunas and tracking metrics with wearables are self-selected to be healthier/more active/etc. Correlation and causation...
If you're watching TV in a sauna you haven't turned the sauna on.
From the article: "..promotes sweating and therefore the elimination of toxins,.."
That false statement really makes me unsure about the quality of the article. And I'm saying this as someone who uses sauna daily, when possible (I have one at home, and I grew up with saunas).
"De-toxification" by sweating is a myth. Sweat glands are very simple organs (think salt on one side, which results in pressure, i.e. osmosis) and can't do anything of the sort. You'll be much better off peeing.
Saunas probably have good health effects. I'm certainly happy as a sauna user. But there's no de-toxification in this.
> 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.
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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
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.
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> Sauna days are more active, which fits how people actually use saunas, often as a post‑workout routine
WAT? As far I as know there is no such connection between workouts and saunas in Finland, nor in Japan
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 :)
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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.
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?
Also not controlled: Maybe on Sauna days they drank more water before bed? Or less alcohol?
Would a hot tub session (say at 100 - 105 F) be comparable or yield similar results?
As someone with access to both Japanese ofuro and sauna, they are quite different in some respects. And similar in others. One thing which a sauna could do for me when the ofuro could not, was to fix a problem I had with coughing. Something which plauged me for a long time, and which the doctors couldn't find any reason for, but I had such painful daily coughs that it really bothered me. Couldn't sleep on my back either. Then I noticed that if I used the sauna daily, and carefully breathed hot air, the symptoms lessened. And after going for the daily sauna regime (instead of occasionally) for some time, the coughing problem I had for years finally disappeared. The hot baths did nothing for this (but was good for other things, e.g. muscle pains. And essential for being able to sleep at cold winter nights in non-insulated Japanese homes.. heating up the body with a very long very hot bath does wonders)
Dr. Rhonda Patrick has been beating the drum for saunas for a long time, and she's reported that a hot tub can be equivalent or better: https://x.com/foundmyfitness/status/1955294334535995850?lang...
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A lot of people go to sauna after workout. I rarely go to sauna without workout so not sure if the combination is helping me or exercise or the sauna. How to control for that?
You are replying to a comment that said they log and control for time of activity.
Appreciate it as a regular sauna-goer. I am also struggling to wake up after sauna evenings and maybe you research explains why
Or the sauna is a relaxing thing like a happy place and that reduces heart rate?
how does this reduction in heartbeat at night affect the body?
Just because your heart rate is lower does it mean you’re any healthier however. This is just ridiculous measurement it means nothing.
The sauna might be acting like any other drug. There are a lot of drugs that will lower nighttime heart rate. Does that mean those drugs are healthier for you?
If your resting heart rate is lower without any drugs, it indicates that your heart can cause sufficient oxygen to be delivered to your organs with less effort than if it were higher. That can be caused by a variety of things (including stroke volume, capillary dilation and general obstruction (or not) of blood vessels). These are all good proxies for general health.
Drugs lowering your resting heart rate do not indicate this in the same way.
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?
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.
That's funny, I find it much easier to fall asleep in a cold environment. Then again, I also like to use a heavy blanket, so maybe it's the weight more than the cold that's helping me.
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Hot shower heats up your body, which causes it to direct blood away from the core to cool it down so it doesn't overheat. Dropping core temp triggers the brain to ramp up melatonin production. Or so I heard.
Conversely, when the temperature drops, your body directs blood away from your hands and legs because core has higher priority for survival
It makes your body cool down, which is desirable for sleep.
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.
A delta of 3 bpm on sauna days corresponds to around 4% delta if the baseline is 72 bpm. I've gone from a resting heart rate over a 7-day average of 64 bpm to 58 bpm by jumping 15 min. of rope a day, 4 times a week. I've lost weight, body fat, and I feel like my body is more efficient with corresponding lower heart rates throughout my active day. I like saunas for recovery and aches, they put me in a relaxed state after, and I believe the dilation is flushing my system. Like anything else, moderation. Perhaps I will add sauna to my weekly routine 1x per week or less.
PSA: if you like saunas but don't have easy access to one, those IR sauna bags you can buy online work great.
Some people find it gross to basically sweat inside a powered sleeping bag, but if you don't mind that you can get the same effects of a sauna while lying on your (covered) couch and watching YouTube.
Wow, they look really quite dangerous. I wouldn’t want to pass out in one. Yeah you can pass out in a sauna too, but it feels easier to lurch for the door than to fight with a sleeping bag.
> I've gone from a resting heart rate over a 7-day average of 64 bpm to 58 bpm by jumping 15 min. of rope a day, 4 times a week.
Over how long of a time period?
My anecdotal experience:
TLDR: regular sauna seems to have no effect on my resting HR. Extended high HR cardio definitely does.
I became a huge fan of sauna time (15-20 minutes at approx 175F/80C... I would prefer a bit warmer, but I had no control). It was like shower time, or meditation time (which I never took time for). Great thinking time. I'd use it after a workout, but I would also use it on days without a workout.
I've been tracking some stats via my Garmin watch for a few years, and I've identified some patterns - particularly regarding resting HR.
The most significant reducer of resting heart rate for me is running (5k). Periods where my training includes regular 5k runs cause my resting HR to drop by 5-8 bpm.
Most of my training is resistance, although in the last 6 months I've added in a lot more cardio. Stairs and rowing do not seem to noticeably reduce my resting HR. Running definitely does. But to be fair, maybe it's not the running but rather the active HR I'm sustaining. Despite trying to stay in the aerobic zone, running always pushes me to zones 4 and 5. So 50% of my 30 minutes of exercise will be in my max zone. With stairs or rowing, I can keep my HR in aerobic and threshold.
Some stats:
When I'm off my fitness routine, living life as a typical person, my resting HR is 65. When I'm on a resistance fitness routine, my resting HR is 58. When I'm also running, the rHR is 51.
If I eat a heavy meal too close to bedtime, my rHR is +15. If I drink a lot of alcohol before sleeping, rHR can be +20! Food + alcohol = WTF. Probably not good.
Can anyone suggest why after covid I can't do Finnish sauna anymore? Prior to that I used to do 1-2x a week a sequence of 5x(10 minutes in sauna + 5 minutes cold water immersion + 10 minutes rest) which was absolutely great for both stress reduction and blood flow. Now if I do 5 minutes in sauna I feel like my skin was burning and I am about to die, and I need to recover for 1 hour from that to be able to just walk away from sauna.
No idea. How hot is and was your sauna? Is it possible that it's hotter than it used to be? Maybe try one that's slightly less hot?
I've got the opposite problem: saunas don't seem to be able to make me sweat anymore, so I'm looking for the hottest saunas I can find.
The usual 95"C, nothing extraordinary. Sweating after covid got impaired, I might have some thermoregulation issue.
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I'm a big fan of soaking in hot water and have noticed that cardiac function seems to have a massive effect on heat tolerance as measured vs body temperature.
For example, if I've been totally sedentary for the whole day (and my feet are chilly+blue), a body temperature as low as 101F is unbearable. But if I've been actively moving around all day (and my feet are warm and pink), I only start getting uncomfortable at a body temperature around 103.5F-104F.
This also seems to correlate over a longer timespan re: exercise habits, consumption habits, sickness, etc.
Shot in the dark, but has your actual stove changed? When have you last changed the stones? Is the circulation of air worse?
If your skin feels hot my guess would be that the steaming effect might be disrupted by the water getting evaporated faster than before, and the circulation of air also affects the skin feel (that’s why a certain seating position can make sauna unbearable). You could also try to just turn it on at the lowest setting and see if it changes anything. Maybe the stones have gotten so old that old heat settings have sneakily turned unbearable.
Did it happen suddenly? Or did you go for a long time without using a sauna, and noticed the change only when you resumed? Did anything else about your body change, such as weight loss (perhaps from a GLP-1)?
It's possible that Covid had nothing to do with it, and your body is simply changing with age. It's depressing, but it happens!
Once in a while as I get sick I have to retrain myself to going to sauna (e.g. taking lowest level, even skipping the Aufguss, German infusion where temperature is raised gradually etc.)
Also IMO your body fat/water/lean muscle ratio may play a role. I once lost 5 kg due to Influenza A and all my sport achievements as well as sauna endurance were gone
anecdotal -but- it took me 6 months after covid for my breathing rate to go back to normal, and to be able to do consistent max our efforts of >190BPM for >5 seconds like previously
After covid I've found i cannot stand the cold. A friend of mine can't stand alcohol since.
I use the sauna every day and highly recommend it to everyone, it's great for your health and for stress
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.
This would not pass peer review for a journal as written.
Maybe the conclusion is correct, or maybe not, but as written the methodology is under specified, statistics are not supported, and there too many confounders not addressed. One should not take anything from this without a better write up. Just misunderstanding what n= means is a huge flag.
Since the author is here, I have to ask: Why a blog post and not an actual paper? Why spray this onto the internet without validating the work? Or, conversely, why not caveat the work as exploratory data science?
I try to do 180 minutes a week of cardio. Mostly Zone 2. Biking, elliptical, tKD. But once in a while my legs feel too tired, so I complete my weekly minutes going to the steam room. It makes sense to me since it raises your heart rate.
Also, my samsung watch can measure stress (whatever it means). It always shows the very, very minimal stress for me. The only time that I have been stressed was the day that I spent a bit too much on the steam room.
FWIW, most of the studies on improvements in blood plasma volume from passive heat are usually done on saunas with temperatures > 150 degrees F (60 C). Steam rooms usually only get up to 120F (~49C) even though the humidity probably makes it feel warmer.
FWIW you should probably be doing some max intensity, or at least high intensity cardio.
Zone 2 is great but the best health outcomes are from people who do high intensity exercise interspersed with zone 2 exercise.
This is contested by a significant number of contemporary running coaches (see, for example "Training for Uphill Athletes" by Steve Johnson or any of the life work of Phil Maffetone.
HIIT is quite effective at something; it's not clear that it is effective at all possible exercise goals (including, but not limited to, endurance running).
Johnson in particular says that unless you've already narrowed the gap between your "first" and "second" (anaerobic) threshold to 5%, HIIT really doesn't make much sense because you're "aerobically challenged" and need to work on that first, which he believes (with significant evidence) is best done almost entirely in zone 2.
He also notes that someone like Eliud Kipchoge can spend 2 hours running 4:30 min/mile pace, so that is clearly within his aerobic range, but that Kipchoge would never and should never spend much time training at that pace because of the load it would put on his system. So the zones that are used for training purposes depend significantly on the current fitness level of the athlete.
I have used HIIT effectively to get myself out of certain fitness/training "ruts", but I think that the zone 2 folks have somevery cogent and coherent observations and advice.
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I also recommend reading about the effects on microplastics studied by Blueprint:
https://cptsd.sites.umassd.edu/bryan-johnson-and-microplasti...
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.
The goal is improving cardiovascular fitness, and a low heart rate means your cardiovascular system is operating efficiently.
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.
No, immediately lowering heart rate isn't a goal of exercise. The reason it's a meaningful measure at all is because a lower resting heart rate, not overnight in response to a stimulus, but a permanently lower resting heart rate, is a sign that your overall cardiorespiratory system has become more efficient in terms of how much blood it can deliver per beat, how much oxygen it can deliver per unit of blood, and how much energy can be generated per unit of oxygen in your mitochondria. When those efficiencies improve, fewer beats per minute results in the same level of work done in your cells. Thus, resting heart acts as a proxy measure of aerobic fitness, not a goal in and of itself. All of those are long-term adaptations. Conversely, there are many ways to acutely lower heart rate that are clearly not healthy. Death, obviously, but taking opioids or many other kinds of depressants, not moving ever, sleeping 23 hours a day, will all lower your average heart rate immediately without making you fitter or healthier.
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.
General advice: citing absolute HR numbers is pretty meaningless for a broad audience, because they are not intepretable. Express them as percentages of your current max HR to be meaningful to others.
As I said, N=1 so the post was meaningless before I said another word :-)
For your benefit: my max is somewhere around 175, maybe 180, which is high for my age.
I'm also unusual in that even my max heart rate doesn't lead to lactic acid buildup, for what it's worth.
N=256
I didn’t see a reference to the amount of time in the sauna required to receive this effect. Was that measured as part of this research?
Should I assume a steam room has the same effect? I prefer it over sauna
Potentially, but likely much less effective and less studied, and you likely need longer sessions for effective dosage.
Most of the studies I've seen on improvements in blood plasma volume from passive heat are usually done with sessions in saunas with temperatures > 150 degrees F (60 C). Steam rooms usually only get up to 120F (~49C) even though the humidity probably makes it feel warmer.
Copying and pasting some of my reply to another comment above
Sweating is one the main triggers for an increase in blood plasma volume, and the humidity level of a steam room causes vastly higher rates of sweating than most saunas do. You can lose significant body heat by sweating in a dry environment, but much less in high humidity. Consequently, your body needs to sweat much more rapidly even though the absolute temperature may be lower.
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I feel better after sitting in a steam room two or three times a week. That's proof enough for me.
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.
Website doesn’t load, it times out. Anyone have tl;dr?
it works for me - what browser are you using?
Its a cloudflare gateway timeout, so not working for anyone on any browser right now. Seems like a contradiction if cloudflare cant cache what is presumably a static site.
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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.
News at 9, shorter people on average live longer than taller people...
Unless you are from Norway or Finland, evidently.
> 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
@dang can fix this right up, I believe
[flagged]
The delta here is your understanding of what a sauna is (or your understanding of the definitions involved), not the reality of what a sauna is.
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.
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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)
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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.
Why is this quackery front page?
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/
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AI;DR
We don't need an acronym; people just need to stop posting these utterly worthless comments.