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Comment by thih9 | Hacker News Reader

> Whereas the risk for sudden cardiac death was 22% lower for men using the sauna 2–3 times per week, the risk was 63% lower for men who used the sauna 4–7 times per week (…)

Aren’t patients with cardiac problems generally discouraged from using sauna? Wouldn’t that be a significant factor in this correlation?

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It’s from a prospective study [1] so the hope is No, as long as the study follows people and their habits for long enough.

Edit: the first men in this study were enrolled in the mid 80s. I always have lots of respect for scientists starting such very long run initiatives. I would imagine it to be boring at times, but hard work begets hard data.

[1] https://clinicaltrials.gov/ct2/show/NCT03221127#:~:text=STUD....

Ideally they would exclude from the study's analysis data any time in which a person was under such advisement to avoid the sauna for cardio reasons.

ideally they would include them and account for them in the analysis, as exclusion presents a confounding variable.

"Accounting for" using e.g. regression techniques is complex guesswork and leaves room for residual confounding. (Just try to imagine how exactly you'd do it in this case!)

There is no perfect solution, but simply excluding problematic data is often the least confounding option.

in this case, the data are not merely problematic, but actually relevant to the study's conclusion. excluding those data is certainly more confounding than including them, because those data are relevant to the conclusion of the study.

Imagine if you did a study on whether air bags in automobiles reduced fatalities, and excluded 'problematic' data involving cases where the occupants were injured by the air bag.

I'm not saying to exclude the event where the person got heart disease. I'm saying to exclude the data after the diagnosis, where the person is avoiding the sauna under doctor's advice.

This isn't difficult to do in a longitudinal study and would indeed be standard in many such studies. You wouldn't want to include data where the arrow of causation is known to run opposite to what you are trying to test for.

In theory these studies keep fixed populations, this is at times surreal as in long term pharmaceutical studies with smaller sample sizes it can happen that the control group ends up taking more of the studied drug than the non-control group.

> 22% lower for men using the sauna 2–3 times per week, the risk was 63% lower for men who used the sauna 4–7 times per week

Extrapolating further, going to the sauna 10-14 times a week would make you immortal.

Checking with my slide ruler, can confirm your calculations are correct.

Extrapolating further, staying in the sauna indefinitely will age you down.

::accidentally falls asleep in the sauna::

::comes out 12 years old::

“Ahh crap!”

Only against sudden cardiac death. You could still get hit by a car.

This is a good point, and was brought up in a response to a study from Laukkanen: https://sci-hub.se/10.1001/jamainternmed.2015.3432

> heart rate increases up to 100 beats/min during sauna sessions at moderate temperatures and up to 150 beats/min during hotter saunas. Although not an issue for healthy individuals, such a cardiac challenge may feel uncomfortable for participants with poor cardiorespiratory fitness and pre-existing disease. Simple adjustment for disease vs no disease may not entirely solve this problem since reverse causation bias (ie, health status affects the likelihood of a sauna session) operates within disease groups; the more severe the disease, the greater the fear of cardiac challenge... A more robust finding at reduced risk of reverse causation bias would be a graded association between number of sauna sessions and mortality in an initially healthy, cardiorespiratory fit population, but this was not observed.

Laukkanen responded with

> ...we did observe graded inverse associations with sudden cardiac death (SCD), fatal coronary heart disease (CHD), and cardiovascular disease (CVD) events, which are the characteristics of a true inverse association between sauna bathing and outcomes. Furthermore, results were carefully adjusted for socioeconomic status (SES), physical activity, and cardiorespiratory fitness...

Notably Laukkanen didn't say that the graded association was in an "initially healthy" population, as the first reply specified.

> Aren’t patients with cardiac problems generally discouraged from using sauna?

If so, I've never heard about it. In Finland, sauna is usually promoted as something that improves cardiovascular health. Associated activities like rolling in the snow or winter bathing is a completely different matter, but it's perfectly possible to enjoy sauna without those.

I'm not a health professional, though, so check with your doctor first if you have heart problems.

This was also my experience in Finland. There were warning signs in some rented sauna’s for jumping into the snow or water after a sauna for people suffering from cardiac problems.

No note about sauna use in general.

In US they basically discourage or warn people not to use sauna if they have any kind of condition, including being pregnant or have been consuming alcohol.

In Finland most pregnant women have always gone to sauna and they haven’t observed any kind of birth defects any more than elsewhere.

Common sense applies and usually expected from adults in Finland. If you start to feel light headed or otherwise bad, you should leave the sauna and drink water or cool off.

ok please describe in detail or advise where I can get the full ritual of sauna in Finland, that sounds like blast.

The participants that suddenly dropped dead during the study were omitted from the results to avoid bias.

Not generally, as far as I know. But of course, you have to be way more careful and conscious if you have a condition.

So maybe not use the hottest sauna and push your limits and maybe no more sauna competitions. (Who can stay the longest, there used to be a world championship in this, but not anymore after one of the finalists - died).

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