“Regular sauna use extends lifespan”

Sauna use tracks with longer life in one carefully followed population. Nobody has tested whether it causes it.

Almost all the mortality evidence comes from a single study: 2,315 middle-aged men in eastern Finland, first examined in the 1980s and followed for a median of about 21 years [1]. Death rates fell as sauna visits rose.

• 295 of the 601 men who went once a week died, about 49%
• 572 of the 1,513 men who went 2 to 3 times a week died, about 38%
• 62 of the 201 men who went 4 to 7 times a week died, about 31%

Deaths from heart and blood vessel disease followed the same pattern, from 22% in the once-a-week group down to 12% in the most frequent group [1]. Longer sessions looked better too, though for total deaths that difference was small enough to be chance [1].

Two things weaken the pattern. Only 201 of the 2,315 men were in the most frequent group, so that 31% rests on 62 deaths. And men who sauna often may differ from men who do not in ways nobody measured.

Where sauna looks best is alongside exercise, not instead of it. In a trial of 47 inactive adults around 49 years old who each had at least one heart disease risk factor, three groups were compared by chance over 8 weeks: exercise plus a 15-minute sauna afterwards, the same exercise alone, or neither [2]. Exercise alone improved fitness and cut fat mass but did not move blood pressure at all [2]. Adding the sauna did: the sauna group ended about 8 points lower on the top number of a blood pressure reading than the exercise-only group, with slightly better fitness and lower total cholesterol [2].

Sauna by itself did less. Forty-one adults with stable coronary artery disease, meaning narrowed heart arteries, were assigned by chance to 8 weeks of sauna four times a week with no exercise added, or to no change in routine [3]. Their bodies clearly adapted to the heat: they sweated more and sat slightly cooler at rest [3]. But blood pressure, artery stiffness and the ability of their arteries to widen did not improve against the control group [3]. One measure of small-vessel blood flow drifted the wrong way in the sauna group, though that shift was not clear-cut [3].

Both trials ran 8 weeks and measured markers in the blood and arteries. Neither followed anyone long enough to count deaths [2][3].

Who this evidence does not describe:

• women, who were absent from the Finnish mortality cohort [1]
• anyone younger than 42 or older than 60 at enrolment in that cohort [1]
• infrared saunas and steam rooms, neither of which is what these men used [1]
• people with unstable heart disease or very low blood pressure, who were not studied [2][3]

In this population, frequent sauna use went with lower death rates, and adding a short sauna after exercise lowered blood pressure over two months. Neither finding shows that sauna sessions will lengthen your own life, and whether a hot sauna is safe alongside an existing heart condition is a question for a doctor rather than for a cohort study.