It may indeed be that there is some extremely nuanced sweet spot

Wednesday, January 26th, 2022

Among 14,000 Finnish people who were tracked for 40 years, those who used saunas frequently were way less likely to develop dementia:

Big if true. And that’s an impressively huge study! But let’s start peeling back the layers.

First of all, it wasn’t every sauna enthusiast who reaped the supposed protective effect against dementia; it was specifically those who used a sauna 9-12 times a month. Sauna bathers who hit the wooden bench 5-8 times a month — sorry, no effect. And those who went more than 12 times a month — again, no luck.

That should raise a caution flag in your head. When only a very specific subpopulation in a study experiences a benefit, it may indeed be that there is some extremely nuanced sweet spot. But it is more likely that the researchers collected a lot of data, which in turn allowed them to analyze many different correlations between sauna use and dementia; the more different analyses they can do, the more likely some of those analyses will generate false positives, just by statistical chance. And then, of course, those titillating positive results are the ones that end up at the top of the paper, and in the press release.

The protection against dementia for that 9-12-times-per-month set was big over the first 20 years of the study, and then faded later, so now we’re slicing and dicing data not only by sauna-frequency, but by time. And then there’s temperature. The Finns who saunaed in temperatures hotter than 100°C (212°F) actually had a higher risk of dementia than those who sauna-and-chilled below 80°C (176°F).

So if you want to prevent dementia, hit the sauna precisely 9-12 times a month at below 80°C — and, unfortunately, expect the protective effect to diminish in the future. Whew!


  1. Sam J. says:

    I suspect there’s something wrong with this study “if” you consider the working mechanism to be “only” that specific use of saunas.

    Maybe people who do this have a certain lifestyle.

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