Sauna: How Many Times a Week for Health and Longevity? What the Research Says

Sauna is one of the few 'biohacking' practices backed by years of data from a large cohort and not only by mechanistic hypotheses. That is why it comes up so often in conversations about longevity. At the same time, the figures that circulate in the media ('sauna lowers the risk of death by 40%') usually lose the context: who was studied, what they were compared with, how long they were followed and how uncertain the confidence intervals are. In this article we focus on one question: what frequency and session length appear in the data and what really follows from that for you.

We do not repeat topics covered separately: the effect of sauna on blood pressure in randomised trials, the differences between traditional and infrared saunas, and the effects on haematocrit, haemoglobin or testosterone. A broader discussion of sauna as an intervention is in our entry on sauna, and on blood pressure in our entry on hypertension.

At first glance the result is impressive: the group using the sauna most often had more than half the proportion of sudden cardiac deaths (5.0% versus 10.1%). But the details need a careful look. First, the crude percentages do not account for differences in age, smoking, blood pressure or other factors; only the adjusted hazard ratio is a fair comparison, and for the highest group it was 0.37 with a wide confidence interval (0.18-0.75), reflecting the small size of that group (201 people). Second, the confidence interval for the group with 2-3 sessions a week (0.57-1.07) included the value 1.0, so that result is not statistically significant.

Third, and this is crucial, the reference group was sauna once a week, not no sauna. So we are talking about the difference between 'once' and 'often', not between 'never' and 'regularly'. That narrows the interpretation: the data do not say what happens to people who never use a sauna. Finally, in Finland sauna is part of everyday life, so people who use it rarely may differ from the rest in ways the data do not describe.

A session in a Finnish sauna (usually 80-100°C) triggers an acute heat response: body temperature rises, skin vessels dilate, heart rate speeds up, often to values similar to moderate exercise, and diastolic pressure falls. Repeated exposure may, according to reviews, improve endothelial function, reduce arterial stiffness and modulate the autonomic nervous system, which biologically resembles some of the effects of endurance training. Heat shock proteins and an anti-inflammatory adaptation are also added to the hypotheses.

It is worth separating mechanism from clinical proof, though. The phenomena above are physiologically real, but that something is biologically plausible does not mean it causes the observed difference in deaths. The only way to settle it would be a large randomised trial with hard endpoints (deaths, heart attacks, strokes), and no such trial has been done: a sauna is difficult to blind and follow-up would have to last many years.

A 'the more often, the better' graph is tempting, which is why it is often described as a 'dose effect'. The observed gradient (1 session, then 2-3, then 4-7 a week) really is consistent with the idea of a dose. But the gradient is also consistent with many other explanations. People who go to the sauna several times a week may be more physically active, have better social support, less stress, more stable health, and may also have a sauna at home, which is usually linked with higher socioeconomic status. The authors adjusted the results for many factors, but in observational studies there is always a risk of unaccounted factors.

On top of that comes reverse causation: people who are developing heart or lung disease or circulatory problems may give up or reduce sauna bathing. In that case lower sauna frequency would be a consequence of approaching illness, not its cause. In studies with long follow-up such an effect is hard to exclude completely. Another matter is the homogeneity of the cohort: the participants are middle-aged men from one region of Finland, so the results need not apply to women, older people or populations with a different culture and lifestyle.

A similar pattern has been described in other analyses of the same cohort. In a study of 1,628 people aged 53-74 (men and women), followed for a median of 14.9 years, 4-7 sessions a week were associated with a hazard ratio for stroke of 0.39 (95% CI 0.18-0.83) versus one session a week, and the result held after adjustment for physical activity and socioeconomic status (0.38). The authors note that the relationship was similar for ischaemic stroke and weaker for haemorrhagic stroke, which may have been due to the small number of events (34).

In an analysis of 2,315 men followed for a median of 20.7 years there were 204 cases of dementia and 123 cases of Alzheimer's disease. Versus one session a week, the hazard ratio for dementia was 0.78 (0.57-1.06) with 2-3 sessions and 0.34 (0.16-0.71) with 4-7 sessions; for Alzheimer's disease 0.80 (0.53-1.20) and 0.35 (0.14-0.90) respectively. With such small numbers in the highest group the confidence intervals are wide, so they should be read as a signal and not a precise estimate.

The cohort data describe sessions in a Finnish sauna, usually at around 80-100°C, often made up of several rounds. A literature review indicates that in experimental studies a sauna lasted usually 5-20 minutes and was repeated 1-3 times during one visit. In the 2015 study, sessions longer than 19 minutes were associated with lower risk than those shorter than 11 minutes, but that effect did not extend to all-cause mortality. This does not mean you must sit for 20 minutes at all costs; it is merely a description of which sessions were typically associated with benefit in this population.

A reasonable approach for a healthy person who is just starting: 1-2 sessions a week of 5-10 minutes, gradually lengthening to 10-20 minutes and 2-3 times a week while watching how you feel. If after a session you get dizziness, palpitations, marked weakness or a headache, that is a signal to shorten the time, lower the temperature or skip it. Entering and leaving should be gradual, not abrupt: after a session it is good to rest for a few minutes sitting before standing up and stepping into a shower.

There is no evidence that increasing frequency above 4-7 times a week gives extra benefits, or that a daily sauna is safe for everyone. In the studies such a high frequency was reported by a small group (201 of 2,315 people), so there are not enough data to assess safety and effectiveness in a wider population.

In clinical reviews, sauna is well tolerated by most healthy adults. Contraindications described include unstable angina, recent heart attack and severe aortic stenosis. People with stable coronary disease or well-controlled hypertension can usually use a sauna, but should discuss it with a doctor, because heat burdens the circulation and blood-pressure-lowering drugs increase the risk of a drop in pressure on standing.

Combining a sauna with alcohol is especially dangerous. A clinical review noted that drinking alcohol in the sauna increases the risk of hypotension, arrhythmia and sudden death and should be avoided. Dehydration adds to this: a session means loss of sweat, so fluids must be replaced afterwards; people taking diuretics are particularly exposed. In pregnancy, sauna in uncomplicated cases in healthy women has not been described as harmful in studies, but because of the risk of overheating it is definitely better to consult the treating doctor beforehand.

A good comparison is the Mediterranean diet or physical activity: there too cohort data point to benefits, but they were gathered in much larger and more varied populations and supplemented with interventional studies. For sauna that level of certainty has not yet been reached, which is why it is sensible to treat it as a pleasant, probably safe for healthy people practice that supports recovery, and not as a proven way to a longer life.

In summary, sauna is one of the better-documented 'longevity' practices in terms of population data, but the level of evidence is moderate, not high. For a healthy person it is most often a safe way to recover and relax that probably supports cardiovascular health; the important thing is not to overrate the promises and not to treat it as a replacement for proven actions such as exercise, blood pressure control, a good diet and sleep.

If you like the sauna, have access to one and are healthy, 2-3 sessions a week of a dozen or so minutes is a reasonable, well-documented pattern that falls within the range observed in studies and does not require extreme practices. There is no basis, however, for buying a home sauna solely in hope of a longer life or for replacing training, hypertension treatment or lipid control with it. Treat it as a pleasant addition to solid foundations and not as a substitute for them.