Data: daily records from wearable users who logged sauna sessions via connected apps. Within-person design — each user is their own control, comparing their own sauna-day nights against their own non-sauna-day nights. No cross-user comparisons.

Stats: paired t-tests, FDR-corrected p < 0.05, Cohen's d > 0.2 threshold for "meaningful effect." Anything below d=0.2 we don't report as a finding.

What we measured: minimum nighttime HR, max and average HR, HRV, activity minutes and distance, menstrual cycle phase (for female subset).

What we found: - On sauna days, minimum nighttime HR drops ~3 bpm (~5%) vs. the same user's non-sauna days. - Effect survives controlling for activity level. It's not "sauna users just exercised more that day." - Strongest hypothesis: elevated parasympathetic tone from the post-sauna cooling phase carries into sleep. Consistent with heat-stress physiology literature. - Sex difference: for women, the nighttime HR effect only crosses the d > 0.2 threshold during the luteal phase. No meaningful effect during the follicular phase. We didn't expect this; worth replicating.

What we can't control for: - Sauna type (dry / infrared / steam), duration, temperature. Not captured. - Dose-response. We don't know session length per user. - Timing of sauna relative to sleep. - Reverse causation: people may sauna on days they already feel recovered. - Selection: wearable users who bother logging sauna are a health-conscious cohort.

What surprised us: the effect is larger than what we see for comparable-intensity exercise days. If you treat nighttime HR as a parasympathetic recovery signal, sauna beats a moderate workout on the same user. Not what I'd have predicted.

The 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.

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.

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.

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.

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