Twenty minutes at 80–100 °C works your heart like a brisk walk. Heart rate climbs to 100–150 beats a minute, vessels open wide, and over a couple of weeks your plasma volume expands and your resting heart rate drops ¹. Those are the adaptations endurance training builds, which is why sauna gets called an exercise mimetic: same engine work, no impact.

The longevity numbers come from Finland, and they hold across endpoints. Versus once-a-week users, the four-to-seven-a-week men had half the fatal cardiovascular disease and 40% fewer deaths from any cause ², roughly 60% less stroke ³, and two-thirds less dementia ⁴. The effect is graded: two to three sessions sits in the middle. The honest catch is that this is cohort data, so healthier people also sauna more; short randomised trials on blood pressure and mood point the same way ⁵.

Most people do this at a gym, which is the realistic way in: a membership with a sauna runs $30–80 a month, and a session is about 2 hours a week door-to-door across 3 visits.

The first hit is that night. People sleep unusually deeply after an evening session, and mood lifts for a couple of hours; one deep-heat session cut depression scores for six weeks ⁵. By six to eight weeks, blood pressure settles and resting heart rate falls a few beats. Across a year, friends notice you look less wound up. Across decades, the cohort gap: the men with thirty years of regular sauna behind them reached old age with half the heart attacks and a third the dementia of their peers ². It's the slowest payoff here and the biggest.