Comment by kyriakosel
18 hours ago
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.
Not saying you are wrong, but I'd like to see some evidence on that. Just because your heart is pumping faster doesn't mean your cardio fitness is getting better. Otherwise we could all just snort cocaine and skip the gym. Alcohol does that too, anyone with a fitness tracker can check that.
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Edit: I posted this accidentally when editing without noticing. Hypertrophy isn't necessarily a bad thing. I thought I was discarding the comment cuz I realized I was out of my depth. whoops
Please ignore my comment, though I will leave it to make the below comments less confusing.
Original: 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.
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For endurance training the main benefit of heat training is raising blood volume. Lungs are not a limiter. Developing stroke volume I imagine requires much higher intensity but that's just a wild guess based on my limited understanding of physiology.
If heat training is better than another interval session remains to be seen but it seems a lot of smart people believe it's worth it nowadays.
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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?...
I recently got an outdoor sauna at home, and that's definitely a key benefit ...sitting in silence without any devices, no smart phones, watches or music for at least 15-20 minutes.
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?)
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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.
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.
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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
Huh what? I can easily sit in a sauna for an hour without breaks as long as it has some type of ventilation.
Smoke saunas a bit less, electric or wood stove saunas no issue. It's nice to take a breather once in a while but I'd honestly have no issues sitting in a 80-90 deg sauna for an hour as long as I have enough to drink with me.
One time I sat in the sauna for six hours with a few breaks between with a group of friends shooting the shit. I had a headache the next morning but I blame it on the Jallu and not the sauna.
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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?
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You are clearly not Finn (/s)
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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.
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...
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> 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/
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> 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.
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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.
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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...
Saunas have not been around longer than exercise.
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.
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?
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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.
It will certainly affect the health of the TV.
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)
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.
> You'll be much better off peeing.
Actually, the rate of blood filtration by kidney glomerulae is pretty constant and independent of the amount of urine in your bladder. Except if you overflow to the point of drowning your kidney of course.
Yes.. my point was only that to get rid of more than water you're better peeing than sweating. In any case, the liver is the only toxin-handling organ in the body (and a complex one).
> 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.
It does, specially if the error bars from multiple measurements show higher precision than what would be expected.
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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.
Unless the effect they're measuring is that the wearable measures differently in sauna days.
Strong conclusion that the hardware is precisely imperfect?
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?
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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
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...
David Roche, a notable running coach (and runner), and his co-coaching wife (and runner) Dr. Megan Roche (MD/PhD) seem to think that hot tubs need to be at least 106F to generate much of a heat shock response, which is normally what one is looking for in the context of post-exercise heat exposure. I should note, however, that they are mostly reading the same research papers as everybody else, not doing primary studies themselves.
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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?