This is the question that separates sauna from most wellness claims, and the answer is unusually good: the long-term outcome data exists.
A 2018 study in BMC Medicine followed 1,688 adults, just over half of them women, for a median of 15 years. Compared with one sauna session per week, the risk of dying from cardiovascular disease was 29% lower with two to three sessions and 70% lower with four to seven sessions, after adjusting for age and sex. The relationship was linear, with no threshold beyond which more sessions stopped helping.
The Finnish Kuopio Ischaemic Heart Disease cohort pushed the follow-up further. Tracking 2,575 men for a median of 27.8 years, a 2023 analysis found that men with high systolic blood pressure who bathed infrequently had 1.81 times the cardiovascular mortality risk of men with normal blood pressure who bathed frequently. Frequent bathing did not erase the risk carried by high blood pressure, but it measurably softened it.
A word of caution about all of it: these are observational cohorts. People who sauna four times a week in Finland may differ from people who sauna once in ways no statistical adjustment fully captures.
What makes the case hold together is the combination. The randomised trials establish that the blood pressure effect is real; the cohorts suggest it translates into outcomes. Neither alone would be convincing. Together they are why cardiology journals now publish reviews on heat therapy as cardiovascular management, including a 2025 review in Frontiers in Cardiovascular Medicine covering sauna use in peripheral arterial disease.