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kyriakosel 1 days 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.
bluGill 1 days ago [-]
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.
nsbk 1 days ago [-]
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.
shmel 23 hours ago [-]
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.
asdfman123 21 hours ago [-]
Athletes already know the answer from years of cultural knowledge, research, and firsthand experience. No, it doesn't make your cardio fitness meaningfully better. If you did sauna training for years and then tried to ramp up for a marathon, you'd be hopelessly out of shape.
Endurance athletes obsessively track VO2 max, basically your body's ability to consume oxygen during workouts, and it certainly doesn't improve with sauna training.
It's like asking "if you only did puzzles, would you be smarter?" Well, in a way, yes, but if you actually want to compete with someone with a good education you have to read.
Same with physical exercise. It puts a lot of different stresses on your body that saunas don't. The question isn't "do saunas make you physically fit," because they don't. The question is "for people who don't want to exercise, does sauna training alone meaningfully extend your healthspan?" I'm guessing the answer is "a little but not enough," but I'm not sure.
monkpit 20 hours ago [-]
You’ve honed in specifically on VO2 but what about cardio health in general? Like light treadmill, not like a demanding marathon.
asdfman123 20 hours ago [-]
Cardio of course is short for "cardiovascular system," which consists of a whole lot of moving parts. Saunas improve some parts of it but certainly not all of it.
Will fixing up your radiator fix your car? Maybe, if the radiator was the problem, but there's a lot of other stuff inside a car to work on, too.
Your body evolved under the expectation that it would be stressed in numerous different ways, but those stressors can all be avoided in the modern era. If you want to most reliably recreate those stresses you need to do cardio and resistance training.
barnabyjones 12 hours ago [-]
Without exercise, you won't burn ATP and thus won't increase mitochondrial count.
nradov 19 hours ago [-]
A light treadmill session won't do much to improve your cardiovascular system health either. I mean it's better than nothing but don't expect too much.
xtracto 22 hours ago [-]
Moreover, I'm from a very hot and humid tropical region. Its normal to ne 40°C with 80% humidity there. And you dont see people having better health or longevity (Yucatan peninsula) .
smileysteve 21 hours ago [-]
40° internal body temperature is not the same as 40° weather.
Yucatan is not the same as Dubai in Summer.
Your body is under heat shock trying to keep up in a Sauna (that isn't considered warm until 60°). Versus a healthy body CAN keep up in 40°.
The Yucatan equivalent of a Sauna is more like doing hard labor on a roof on a sunny day with no breeze.
Tor3 13 hours ago [-]
Right, it's just that a sauna at 60 degrees is not warm, it's cold. Take a shower, go into the sauna at 60 degrees C, and it'll feel cold. Nothing happens in a sauna until you're getting near 80, and it's much better if you go somewhat higher (90 or more for active users). 60 is when a sauna will be closed off in public baths because there's a technical problem somewhere.
Insanity 22 hours ago [-]
The great but not super healthy Mexican diet might offset the potential heat exposure benefits! Although I’m basing that on the diet of my Monterrey-based in-laws, not sure how different Yucatan is.
xtracto 21 hours ago [-]
LOL, Monterrey diet is healthy compared to the diet in the Yucatan peninsula.
Tamales, Cochinita (roasted pork with herbs), salbutes, trancas. Everything of course cooked in Lard. With CocaCola on the side.
So yeah, that's a strong point.
cpursley 14 hours ago [-]
Lard is fine as is pork, it’s the sugar and carbs.
actionfromafar 22 hours ago [-]
But that would be like exercise all the time which may not be optimal. (Not saying the theory holds that sauna equals exercise, but if it does, sauna all the time may not be great. Plus, there may be other confounding factors with living in various locations.)
mminer237 24 hours ago [-]
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.
kiritanpo 23 hours ago [-]
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.
kazga 23 hours ago [-]
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.
gf000 21 hours ago [-]
I would assume that another factor is that the technique for a given exercise on the other hand can be improved, and that can help with decreasing the necessary energy - would that be a correct statement? And as a follow up, depending on activity type this may or may not be significant?
frocodillo 20 hours ago [-]
Yes, definitely. Technique is partly about efficient mechanical movement, sending the various parts of your body in the right direction(s) and not waste effort on movement that doesn’t contribute to propelling you forwards. But for endurance sports, it’s really about minimizing energy cost at a given speed. To use running as an example, you can improve biomechanical efficiency through better timing, correct loading of tendons, tendon stiffness, elastic energy use, and more.
bluGill 23 hours ago [-]
You kind of can - the muscles can use aerobic or anaerobic processes. When you develop brute strength you are training those anaerobic processes. That isn't what OP was talking about, and overall it is much less energy efficient, but it does produce a large burst of energy when needed and you can train your muscles that way.
SJMG 23 hours ago [-]
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 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.
robrenaud 23 hours ago [-]
The flat earthers are why I hate astronomy.
Afaict, the grand parent poster is just very wrong. You do want to cause acute stresses to your heart (cardiovascular exercise) to get it work better.
groundzeros2015 23 hours ago [-]
It’s not really about this particular claim. It’s that I can read a comment that has a reasonable chain of logic and I don’t know if it’s true. This topic is just not easily studied and theories are hard to falsify.
groundzeros2015 19 hours ago [-]
Claims about flat earth are falsifiable with at-home experiment.
rhyperior 24 hours ago [-]
That seems… misguided.
Sources?
jagged-chisel 23 hours ago [-]
Your heart is also a muscle.
PaulDavisThe1st 15 hours ago [-]
... about the size of your fist. Keep loving, keep fighting.
(attributed to Bertolt Brecht)
bluecalm 21 hours ago [-]
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.
PaulDavisThe1st 15 hours ago [-]
and specifically, to be clear, plasma volume.
pegasus 22 hours ago [-]
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?...
willnz 15 hours ago [-]
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.
kyriakosel 1 days ago [-]
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
lfuller 24 hours ago [-]
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.
HelloMcFly 24 hours ago [-]
> 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.
gjulianm 23 hours ago [-]
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?)
HelloMcFly 17 hours ago [-]
Much of it is, sure, but certainly not all of it! On your comparison to Sweden, be cautious! Finns generally have a higher risk and incidence of cardiovascular disease compared to native Swedes - in fact, they have some of the highest risk in the world!
Research from Earric Lee and/or Jari Laukkanen from this past decade will have clinical trials with controlled groups rather than just long-term population tracking. There are within-Finland studies comparing high-risk Finns who use the sauna 4 to 7 times a week against high-risk Finns who use it only once a week, showing a clear effect (https://pubmed.ncbi.nlm.nih.gov/25705824/). Here is a non-randomized experiment showing a dose-response (https://pubmed.ncbi.nlm.nih.gov/29048215/).
Those are just indications of information available. I would also argue that while of course randomized experiments are ideal, it is a mistake to dismiss all other forms of evidence so readily, especially with such preponderance of it.
gjulianm 16 hours ago [-]
The first study shows a 0.37 hazard ratio for frequent sauna use. That’s better than a lot of the HRs reported for physical activity. It’s even better than not smoking. It just doesn’t really fit.
Also, the fact that there are practically no sauna related studies outside of Nordic populations is suspicious too. I bet that with those hazards ratios a lot of people have tried to study the effects more, it’s suspicious there’s practically nothing out there.
HelloMcFly 13 hours ago [-]
There's more research for you to explore if you're interested, but you sound more closed than curious if I'm honest. Maybe looking more into it will change your mind, maybe not!
gjulianm 6 hours ago [-]
I explored quite a bit because I was curious to see how it was possible that sauna had these great effects and why no one used it outside of Finland. But to this point I haven’t seen anything that really supports the idea that sauna is such a massive health protector as claimed. It’s probably beneficial, yes, but the real benefits are probably far lower than claimed.
nyjah 24 hours ago [-]
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.
tuukkah 23 hours ago [-]
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.
Tor3 13 hours ago [-]
Yep. A problem with public saunas (outside Finland, at least) is that they lower the temperature (to, say below 80) in the misguided belief that this will make it easier for more people to stay longer inside.. which is the wrong way to use a sauna. A sauna should be hot enough that you'll go out when it starts feeling too hot (or hard), not so cold that you'll go outside when you're getting bored. With a hot sauna small children can leave after one or two minutes, some people leave after five, others after ten, and in any case go outside and cool down with a showre (or a lake..), then go back in.
iammjm 23 hours ago [-]
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
httpsterio 23 hours ago [-]
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.
Tor3 13 hours ago [-]
At which temperature?
bluGill 23 hours ago [-]
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?
Tor3 13 hours ago [-]
Don't "tough it out" in a sauna. Stay until it feels uncomfortable, or, if you're not sure, keep track of your heart rate and get out if it increases too much. You'll get used to the sauna after frequenting it for some time, which usually results in being able to stay longer before it feels uncomfortable. Your ability to sweat will improve, for example, including being able to sweat on body parts where you may initially be unable to (it took a long time before my wife's calves "learned" to sweat, for example).
MyHonestOpinon 21 hours ago [-]
IMHO. 10-20 mins is good enough. I wouldn't try to stay for an hour.
If 10mins feels too much, do less.
theshrike79 20 hours ago [-]
30 seconds? What kind of torture room of a sauna are you going in?
marssaxman 19 hours ago [-]
Heat tolerance varies. For some of us, all saunas feel like torture rooms!
trklausss 23 hours ago [-]
You are clearly not Finn (/s)
nyjah 20 hours ago [-]
lol, this is true. Wish I could tolerate it longer like a proper Finn. I’ll go 25 mins occasionally but mostly I do 15 mins, break, another 5-10 mins..
jampekka 20 hours ago [-]
Finns don't do it that long. It's typically 5-15 minutes per sitting, with 2-4 sittings per session.
nyjah 17 hours ago [-]
My answer was sarcastic back, fwiw, I follow the 'proper' finnish ritual or similar...
jjallen 22 hours ago [-]
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.
ricardobayes 24 hours ago [-]
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.
You're saying that crime leads to longevity? Big if true.
taeric 22 hours ago [-]
I think the claim is more that if you provide financial support for X without solid record keeping to verify X, expect that you will get more self reported people in that description.
Put differently, relying on self reporting for any sort of status from people is just not a reliable methodology.
yxhuvud 22 hours ago [-]
No, he is saying bad record keeping means misreporting identity has a bigger chance of happening.
projektfu 22 hours ago [-]
Fraud leads to people officially living beyond their natural death, yes.
RankingMember 24 hours ago [-]
> 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.:
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?
brushfoot 24 hours ago [-]
> 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.
trklausss 23 hours ago [-]
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.
15 hours ago [-]
bluGill 24 hours ago [-]
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.
shevy-java 23 hours ago [-]
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.
Tor3 13 hours ago [-]
Saunas are common in Norway, even if not to the same degree as in Finland.
The reason Finland has had a lower life expectancy than Norway is believed to be due to the difference in diet (cardivascular issues). Note that the diet in Finland has changed quite a lot over the last decades and these differences will presumably level out, statistically.
smileysteve 20 hours ago [-]
Your comparison reads to suggest that Japan doesn't have Onsen culture or that sauna does not exist in Norway.
That's to say, many cultures from around the globe have developed similar activities that heat the body.
bluGill 23 hours ago [-]
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?
gonzalohm 23 hours ago [-]
A lot of Mediterranean countries also have high life expectancy and are the opposite of a sauna culture.
kyriakosel 23 hours ago [-]
Cyprus summers are like 45C and its almost like a sauna :)
GordonS 23 hours ago [-]
Maybe eating a lot of fish, rather than meat, has an impact too.
bwestergard 24 hours ago [-]
The "blue-zone" studies are flawed, so we shouldn't infer too much from lifestyle generalizations about people in them.
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.
havella 11 hours ago [-]
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.
sonink 24 hours ago [-]
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.
Jtarii 24 hours ago [-]
A sauna will do nothing for muscular-skeletal health.
derektank 24 hours ago [-]
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?
Jtarii 19 hours ago [-]
>which have beneficial effects on muscle growth and repair?
Repair from what?
testing22321 1 days ago [-]
I don’t think the TV in the sauna will have long term health outcomes.
Filligree 24 hours ago [-]
It will certainly affect the health of the TV.
jmdeon 21 hours ago [-]
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.
tester756 23 hours ago [-]
One hour in sauna? :O
bluGill 23 hours ago [-]
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)
throwaway-blaze 19 hours ago [-]
Even more likely is those using saunas and tracking metrics with wearables are self-selected to be healthier/more active/etc. Correlation and causation...
iso1631 20 hours ago [-]
If you're watching TV in a sauna you haven't turned the sauna on.
Tor3 13 hours ago [-]
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.
Ey7NFZ3P0nzAe 9 hours ago [-]
> 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.
Tor3 8 hours ago [-]
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).
majkinetor 5 hours ago [-]
Actually, this is why one shouldn't believe HN comments about medicine. The quality is this low.
This is simply laughable and very easily checked out. Here is one random study:
> Sweating deserves consideration for toxic element detoxification.
Its even observable directly - just go next to the heavy smoker during exercise.
While it might be less than dedicated organs, the skin is the largest organ by far.
Ofc, the topic is debated like every single thing in medicine, but calling it a myth is nonsence.
Tor3 1 hours ago [-]
First, you don't need to go through any kind of "detox" regime. That's myth 1. The liver is where natural detoxing occurs, and the kidneys filters the rest. Don't focus on detox, instead focus on keeping your liver healthy (alcohol, fat..)
Secondly, the sweat glands don't have any kind of functionality outside of pressing water out of the body. The water may happen (depending on how small the molecule is) to bring other stuff with it, but that's hardly "detox". Just pee instead!
The whole "detox" trend is just that - a trend, a meme. Focus on other elements of health instead, eat healthy, and don't interrupt that with some tiktok "detox" scheme.
gjulianm 23 hours ago [-]
> 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?
jampekka 23 hours ago [-]
> 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.
gjulianm 23 hours ago [-]
It does, specially if the error bars from multiple measurements show higher precision than what would be expected.
jampekka 22 hours ago [-]
I don't understand what you mean by that.
Precision (inverse of variance) of estimate of mean increases directly proportional to number of samples (given some assumptions that very likely hold here). If you have measurement standard deviation of say 10 bpm, with 100 measurements you have mean estimate standard deviation of 10/sqrt(100) = 1 bpm.
gjulianm 22 hours ago [-]
> of estimate of mean
But you can't really assume that the estimate of the mean represents the real value. For example, if the sensor is equally likely to show 80 or 81 BPM when the real heartrate is 80.7, the mean estimator will be biased.
> with 100 measurements
Also, wearables aren't taking 100 measurements of the BPM at a given point in time. I think the highest frequency they usually have is 1 second measurement interval. So they don't really have a lot of measurements for each point in time.
> mean estimate standard deviation
That's the standard deviation of the mean of the values. Doesn't imply that the standard deviation of the values themselves will go to zero.
> I don't understand what you mean by that.
That as a rule of thumb, you should not assume that repeating measurements will give you more precision than what the tool can offer. E.g., trying to measure down to milimeters with a ruler that has only 1cm marks will not really work well.
jampekka 22 hours ago [-]
> But you can't really assume that the estimate of the mean represents the real value. For example, if the sensor is equally likely to show 80 or 81 BPM when the real heartrate is 80.7, the mean estimator will be biased.
Bias is different from precision. If both conditions have the same bias, their difference is still unbiased.
> Also, wearables aren't taking 100 measurements of the BPM at a given point in time. I think the highest frequency they usually have is 1 second measurement interval. So they don't really have a lot of measurements for each point in time.
I did not mean taking multiple measurements in succession. Those are likely to have correlated noise, meaning the assumptions do not hold. But between participants measurement noise is very unlikely to be correlated.
> That as a rule of thumb, you should not assume that repeating measurements will give you more precision than what the tool can offer. E.g., trying to measure down to milimeters with a ruler that has only 1cm marks will not really work well.
If you quantize so much that you have no variance in the measurements, then sure. But watches typically have 1 bpm quantization, which is fine at the scale of variation in HR.
If you have independent error in measurements and quantization that gives you variance in measurement, you very much can assume repeating measurements will give you more precision than the tool can offer. This is how e.g. particle physics (and many many other fields of science) is done.
gjulianm 16 hours ago [-]
> Bias is different from precision. If both conditions have the same bias, their difference is still unbiased.
Not really, and I wouldn’t assume that when the condition under study can also affect how the measurement is taken.
> If you quantize so much that you have no variance in the measurements, then sure. But watches typically have 1 bpm quantization, which is fine at the scale of variation in HR.
At the scale of variation in HR in general yes, but not if the difference you’re trying to measure is in the range of 3 BPM.
> If you have independent error in measurements and quantization that gives you variance in measurement
That’s a big if. I am not confident we can claim that the errors are independent in this case, using sauna or not can affect how the sensor measures BPM.
jampekka 23 hours ago [-]
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
lccerina 24 hours ago [-]
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?
joelthelion 24 hours ago [-]
> 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.
gjulianm 24 hours ago [-]
Unless the effect they're measuring is that the wearable measures differently in sauna days.
ranguna 24 hours ago [-]
Strong conclusion that the hardware is precisely imperfect?
gamerslexus 1 days ago [-]
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...
kyriakosel 1 days ago [-]
we agree - but thats not that simple :)
methyl 24 hours ago [-]
> 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?
kyriakosel 24 hours ago [-]
i was mostly refering to humidity/duration/temperature given that most devices do not report back these values
austinthetaco 23 hours ago [-]
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.
PaulDavisThe1st 15 hours ago [-]
There's quite a wide range of variation between "full dry" (no added humidity whatsoever) and "full steam" (an actual steam room, rather than a sauna). Just asking people was it dry or was it humid won't capture much of that variation. I have a steam room at home and have been a near-life-long lover of them - they are wildly different than a sauna. But I'd still rank a sauna where someone had dumped 1L or so of water over the heater to be "humid", and consider it also very different from a totally dry sauna.
gamerslexus 20 hours ago [-]
What if they jumped between saunas? And with self-reporting, the more you ask I guess the less precise the result... Sensors, however...
socalgal2 14 hours ago [-]
> 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
al_borland 23 hours ago [-]
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.
verst 23 hours ago [-]
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.
jtanderson 24 hours ago [-]
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?
oidar 22 hours ago [-]
Also not controlled: Maybe on Sauna days they drank more water before bed? Or less alcohol?
lazyant 23 hours ago [-]
Would a hot tub session (say at 100 - 105 F) be comparable or yield similar results?
Tor3 13 hours ago [-]
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)
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.
pstuart 14 hours ago [-]
Being that the recommended max temperature for hot tubs is 104F that could be an issue. Hot tubs are definitely more pleasurable than saunas, and if it comes "close enough" I'd be fine with that.
alfiedotwtf 3 hours ago [-]
Time of day could make a huge difference - if they did this close to sleeping, their body would be hot while winding down, and so would use less layers. If they fell asleep with only a sheet compared to multi-layered thick covers, their temperature would be lower for the whole night.
I know n=1, but when I started sleeping with only a sheet, my heart rate was at my lowest - my Apple Watch would ping multiple times a night because it was below 40.
Can’t comment about being cold anymore because these days I sleep on top of a spiked mat which makes my back feel like it’s on fire for the whole night.
vinni2 21 hours ago [-]
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?
marcosdumay 21 hours ago [-]
You are replying to a comment that said they log and control for time of activity.
p1anecrazy 22 hours ago [-]
Appreciate it as a regular sauna-goer. I am also struggling to wake up after sauna evenings and maybe you research explains why
Glemllksdf 23 hours ago [-]
Or the sauna is a relaxing thing like a happy place and that reduces heart rate?
11 hours ago [-]
itsthecourier 1 days ago [-]
how does this reduction in heartbeat at night affect the body?
Noaidi 23 hours ago [-]
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?
PaulDavisThe1st 15 hours ago [-]
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.
Noaidi 3 hours ago [-]
You think being n a Sauna is not a drug (effectively)?
croemer 1 days ago [-]
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?
strangescript 24 hours ago [-]
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.
Arch485 23 hours ago [-]
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.
something765478 20 hours ago [-]
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.
WastedCucumber 19 hours ago [-]
I think that's also consistent with the idea behind a hot shower. The shower doesn't help by increasing your body temperature, in fact it does the opposite. The hot shower induces the body to try to cool down, so near-skin blood vessels swell, and that dumps heat into the cold air, which reduces your core temperature, and a reduced core temperature helps you fall asleep.
I think where I read about this was Why We Sleep from Matthew Walker. But he suggests just washing your face with warm water, as opposed to a shower.
pawelduda 18 hours ago [-]
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
theshrike79 3 hours ago [-]
One trick I've heard is doing squats just before getting into bed. Just body weight.
It increases blood flow in your legs, which lowers your blood pressure -> lights out faster.
sva_ 23 hours ago [-]
It makes your body cool down, which is desirable for sleep.
Aurornis 1 days ago [-]
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.
eggy 23 hours ago [-]
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.
asdfman123 20 hours ago [-]
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.
sd9 15 hours ago [-]
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.
jrussino 19 hours ago [-]
> 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?
theshrike79 3 hours ago [-]
Correct me if I'm wrong, but I thought HRV (Heart Rate Variability) is a bigger positive correlation for health than low heart rate?
YmiYugy 23 hours ago [-]
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.
storus 23 hours ago [-]
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.
rags2riches 4 hours ago [-]
Is the stove radiating too much heat? You want it to heat the air, not fry your skin! I once got a stove glowing hot because I had failed to get a high enough temperature going on the day before. It was the first time I tried a wood fired sauna myself. As long as the stove was glowing hot, I just couldn't enjoy the sauna.
mcv 23 hours ago [-]
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.
storus 23 hours ago [-]
The usual 95"C, nothing extraordinary. Sweating after covid got impaired, I might have some thermoregulation issue.
mcv 22 hours ago [-]
95 is pretty hot. At commercial spas I see them start at 70, and rarely above 90.
storus 22 hours ago [-]
95 is normal where I live for Finnish saunas. Then there are other types of saunas that start lower, but Finnish are always around 95.
jampekka 21 hours ago [-]
95 is high for Finnish saunas in Finland at least. Public saunas are very rarely so hot here, and few like it that hot.
Edit: to put it into some numbers, per one study[1] Finnish sauna sessions were on average at 75.9°C with SD 9.9°C. If we assume normal distribution, that means that more than 97 % of sauna sessions are at < 95°C.
I actually like them that hot. I look for 90+ saunas, and once was in one that claimed to be over 100. Although I have no idea how accurate that is. They're very bearable to me. But if they're not bearable, of course you should look for a sauna that's not quite as hot. Or at least stay low; the higher you sit, the hotter it is.
jampekka 9 hours ago [-]
You can have over 100°C. The amount of steam is a crucial factor. Even over 100°C doesn't feel that hot if it's dry, but at higher temperatures the "löyly profile" often becomes quite harsh.
xkcd-sucks 21 hours ago [-]
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.
originalvichy 18 hours ago [-]
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.
sowbug 19 hours ago [-]
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!
p1anecrazy 22 hours ago [-]
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
kyriakosel 17 hours ago [-]
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
Ylpertnodi 23 hours ago [-]
After covid I've found i cannot stand the cold. A friend of mine can't stand alcohol since.
SCdF 24 hours ago [-]
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.
asdfman123 20 hours ago [-]
The goal is improving cardiovascular fitness, and a low heart rate means your cardiovascular system is operating efficiently.
SJMG 23 hours ago [-]
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.
nonameiguess 22 hours ago [-]
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.
manapause 9 hours ago [-]
As an amateur sauna evangelist, I can say my experience sauna usage 1-2 times a week has greatly improved my life and quality of sleep!
chris_va 23 hours ago [-]
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?
kp988 15 hours ago [-]
I use the sauna every day and highly recommend it to everyone, it's great for your health and for stress
MyHonestOpinon 21 hours ago [-]
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.
dtran 16 hours ago [-]
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.
asdfman123 21 hours ago [-]
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.
PaulDavisThe1st 15 hours ago [-]
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.
mchusma 13 hours ago [-]
I think one issue I have with Zone 2 proponents is that it makes sense that if you can do a lot more stuff at Zone 2 than you can at less. For most endurance athletes, the volume of running beats everything else in terms of efficacy. However, most of us don't have unlimited time.
For example, if I do a week of 3x30 minute swssions at Zone 2, my fitness is going to plummet. But if I do one at Zone 2, one at tempo, and one set of intervals, I'm at least maintaining fitness.
Would 5 hours at zone 2 be better? Absolutely. But I dont always have the time.
dilyevsky 13 hours ago [-]
Only z2 is for complete noobs. UA actually recommends 80/20 split between z1 and upper z3
9 hours ago [-]
vitto_gioda 21 hours ago [-]
I also recommend reading about the effects on microplastics studied by Blueprint:
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.
gcanyon 24 hours ago [-]
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.
PaulDavisThe1st 15 hours ago [-]
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.
gcanyon 12 hours ago [-]
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.
1 days ago [-]
amazingamazing 24 hours ago [-]
N=256
redeux 23 hours ago [-]
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?
atum47 20 hours ago [-]
Should I assume a steam room has the same effect? I prefer it over sauna
kyriakosel 2 hours ago [-]
that would be interesting to study - let me follow up on this
dtran 16 hours ago [-]
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
PaulDavisThe1st 15 hours ago [-]
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.
dtran 14 hours ago [-]
To my understanding, while sweating is important to heat adaptation and blood plasma volume adaptations, thermal load and cardiovascular strain are likely bigger factors (and more important for the health benefits mentioned in this study). Overall thermal load is still higher in a hotter dry sauna than in a steam room
PaulDavisThe1st 14 hours ago [-]
That's not my understanding, but my understanding is somehwere between 3rd and 6th hand, so it's likely not worth much.
ckrapu 1 days ago [-]
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.
flippyhead 1 days ago [-]
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".
thundergolfer 24 hours ago [-]
This article is a brilliant skewering of the 'em dash means LLM' heuristic as a broken trick deployed by those too-clever-by-half.
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.
eudamoniac 23 hours ago [-]
AI;DR
WaltPurvis 22 hours ago [-]
We don't need an acronym; people just need to stop posting these utterly worthless comments.
smm11 21 hours ago [-]
I feel better after sitting in a steam room two or three times a week. That's proof enough for me.
dukeofdoom 23 hours ago [-]
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.
iwontberude 24 hours ago [-]
Website doesn’t load, it times out. Anyone have tl;dr?
kyriakosel 24 hours ago [-]
it works for me - what browser are you using?
cpncrunch 21 hours ago [-]
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.
kyriakosel 18 hours ago [-]
indeed - fixed now, let me know if you can see it!
cpncrunch 6 hours ago [-]
Yes working now.
kyriakosel 2 hours ago [-]
great
shevy-java 24 hours ago [-]
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.
chasebank 14 hours ago [-]
News at 9, shorter people on average live longer than taller people...
movie_fan25 13 hours ago [-]
Unless you are from Norway or Finland, evidently.
sva_ 1 days ago [-]
> 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
kyriakosel 24 hours ago [-]
Fair flag: 256 users, 59k days
deviation 23 hours ago [-]
@dang can fix this right up, I believe
stevekemp 1 days ago [-]
[flagged]
gaoshan 23 hours ago [-]
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.
> 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.
danlitt 24 hours ago [-]
This just means the surfaces are dry. The commenter said the air is not dry.
weird-eye-issue 23 hours ago [-]
Putting water on hot stones in a sauna does not raise the humidity nearly as much as you think it does.
barbazoo 1 days ago [-]
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.
There are different kinds of saunas. Nobody gets into a 90c humid sauna, that would just kill you.
preya2k 1 days ago [-]
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.
renewiltord 23 hours ago [-]
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.
hilariously 1 days ago [-]
I guess I am a revenant - I get into one regularly in my basement.
victorbjorklund 24 hours ago [-]
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)
KeplerBoy 24 hours ago [-]
the point is the humidity. hot saunas need to be relatively dry otherwise your sweat won't evaporate.
24 hours ago [-]
LeCompteSftware 1 days ago [-]
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.
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.
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.
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.
Endurance athletes obsessively track VO2 max, basically your body's ability to consume oxygen during workouts, and it certainly doesn't improve with sauna training.
It's like asking "if you only did puzzles, would you be smarter?" Well, in a way, yes, but if you actually want to compete with someone with a good education you have to read.
Same with physical exercise. It puts a lot of different stresses on your body that saunas don't. The question isn't "do saunas make you physically fit," because they don't. The question is "for people who don't want to exercise, does sauna training alone meaningfully extend your healthspan?" I'm guessing the answer is "a little but not enough," but I'm not sure.
Will fixing up your radiator fix your car? Maybe, if the radiator was the problem, but there's a lot of other stuff inside a car to work on, too.
Your body evolved under the expectation that it would be stressed in numerous different ways, but those stressors can all be avoided in the modern era. If you want to most reliably recreate those stresses you need to do cardio and resistance training.
Yucatan is not the same as Dubai in Summer.
Your body is under heat shock trying to keep up in a Sauna (that isn't considered warm until 60°). Versus a healthy body CAN keep up in 40°.
The Yucatan equivalent of a Sauna is more like doing hard labor on a roof on a sunny day with no breeze.
Tamales, Cochinita (roasted pork with herbs), salbutes, trancas. Everything of course cooked in Lard. With CocaCola on the side.
So yeah, that's a strong point.
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.
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.
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.
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.
Afaict, the grand parent poster is just very wrong. You do want to cause acute stresses to your heart (cardiovascular exercise) to get it work better.
Sources?
(attributed to Bertolt Brecht)
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.
Agreed on the long-term effect too: doing a study on long term health is a completely different story
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.
Research from Earric Lee and/or Jari Laukkanen from this past decade will have clinical trials with controlled groups rather than just long-term population tracking. There are within-Finland studies comparing high-risk Finns who use the sauna 4 to 7 times a week against high-risk Finns who use it only once a week, showing a clear effect (https://pubmed.ncbi.nlm.nih.gov/25705824/). Here is a non-randomized experiment showing a dose-response (https://pubmed.ncbi.nlm.nih.gov/29048215/).
Those are just indications of information available. I would also argue that while of course randomized experiments are ideal, it is a mistake to dismiss all other forms of evidence so readily, especially with such preponderance of it.
Also, the fact that there are practically no sauna related studies outside of Nordic populations is suspicious too. I bet that with those hazards ratios a lot of people have tried to study the effects more, it’s suspicious there’s practically nothing out there.
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.
If 10mins feels too much, do less.
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.
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.
Put differently, relying on self reporting for any sort of status from people is just not a reliable methodology.
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/
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?
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.
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.
That's to say, many cultures from around the globe have developed similar activities that heat the body.
https://www.science.org/content/article/do-blue-zones-suppos...
Repair from what?
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.
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.
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.
This is simply laughable and very easily checked out. Here is one random study:
https://link.springer.com/article/10.1007/s00244-010-9611-5
> Many toxic elements appeared to be preferentially excreted through sweat
Here is another quick one
https://onlinelibrary.wiley.com/doi/full/10.1155/2012/184745
> Sweating deserves consideration for toxic element detoxification.
Its even observable directly - just go next to the heavy smoker during exercise.
While it might be less than dedicated organs, the skin is the largest organ by far.
Ofc, the topic is debated like every single thing in medicine, but calling it a myth is nonsence.
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?
For large sample averages this doesn't really matter.
Precision (inverse of variance) of estimate of mean increases directly proportional to number of samples (given some assumptions that very likely hold here). If you have measurement standard deviation of say 10 bpm, with 100 measurements you have mean estimate standard deviation of 10/sqrt(100) = 1 bpm.
But you can't really assume that the estimate of the mean represents the real value. For example, if the sensor is equally likely to show 80 or 81 BPM when the real heartrate is 80.7, the mean estimator will be biased.
> with 100 measurements
Also, wearables aren't taking 100 measurements of the BPM at a given point in time. I think the highest frequency they usually have is 1 second measurement interval. So they don't really have a lot of measurements for each point in time.
> mean estimate standard deviation
That's the standard deviation of the mean of the values. Doesn't imply that the standard deviation of the values themselves will go to zero.
> I don't understand what you mean by that.
That as a rule of thumb, you should not assume that repeating measurements will give you more precision than what the tool can offer. E.g., trying to measure down to milimeters with a ruler that has only 1cm marks will not really work well.
Bias is different from precision. If both conditions have the same bias, their difference is still unbiased.
> Also, wearables aren't taking 100 measurements of the BPM at a given point in time. I think the highest frequency they usually have is 1 second measurement interval. So they don't really have a lot of measurements for each point in time.
I did not mean taking multiple measurements in succession. Those are likely to have correlated noise, meaning the assumptions do not hold. But between participants measurement noise is very unlikely to be correlated.
> That as a rule of thumb, you should not assume that repeating measurements will give you more precision than what the tool can offer. E.g., trying to measure down to milimeters with a ruler that has only 1cm marks will not really work well.
If you quantize so much that you have no variance in the measurements, then sure. But watches typically have 1 bpm quantization, which is fine at the scale of variation in HR.
If you have independent error in measurements and quantization that gives you variance in measurement, you very much can assume repeating measurements will give you more precision than the tool can offer. This is how e.g. particle physics (and many many other fields of science) is done.
Not really, and I wouldn’t assume that when the condition under study can also affect how the measurement is taken.
> If you quantize so much that you have no variance in the measurements, then sure. But watches typically have 1 bpm quantization, which is fine at the scale of variation in HR.
At the scale of variation in HR in general yes, but not if the difference you’re trying to measure is in the range of 3 BPM.
> If you have independent error in measurements and quantization that gives you variance in measurement
That’s a big if. I am not confident we can claim that the errors are independent in this case, using sauna or not can affect how the sensor measures BPM.
- 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
- 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?
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.
> 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...
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?
WAT? As far I as know there is no such connection between workouts and saunas in Finland, nor in Japan
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.
I know n=1, but when I started sleeping with only a sheet, my heart rate was at my lowest - my Apple Watch would ping multiple times a night because it was below 40.
Can’t comment about being cold anymore because these days I sleep on top of a spiked mat which makes my back feel like it’s on fire for the whole night.
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?
Drugs lowering your resting heart rate do not indicate this in the same way.
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 think where I read about this was Why We Sleep from Matthew Walker. But he suggests just washing your face with warm water, as opposed to a shower.
Conversely, when the temperature drops, your body directs blood away from your hands and legs because core has higher priority for survival
It increases blood flow in your legs, which lowers your blood pressure -> lights out faster.
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.
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.
Over how long of a time period?
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.
Edit: to put it into some numbers, per one study[1] Finnish sauna sessions were on average at 75.9°C with SD 9.9°C. If we assume normal distribution, that means that more than 97 % of sauna sessions are at < 95°C.
[1] https://pmc.ncbi.nlm.nih.gov/articles/PMC6262976/
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.
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.
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!
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
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.
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.
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?
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.
Zone 2 is great but the best health outcomes are from people who do high intensity exercise interspersed with zone 2 exercise.
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.
For example, if I do a week of 3x30 minute swssions at Zone 2, my fitness is going to plummet. But if I do one at Zone 2, one at tempo, and one set of intervals, I'm at least maintaining fitness.
Would 5 hours at zone 2 be better? Absolutely. But I dont always have the time.
https://cptsd.sites.umassd.edu/bryan-johnson-and-microplasti...
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.
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.
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
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".
1. https://www.scottsmitelli.com/articles/em-dash-tool/
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.
Editorialized title is wrong. n=256
> 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.
> 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
EDIT: I guess it depends on your definition of "humid". But 90C and regular water infusions are pretty common sauna conditions.
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-...