“Regular sauna use helps you live longer.”

The research found this

Researchers recruited 2,682 men aged 42 to 60 from Kuopio in eastern Finland between 1984 and 1989 for a heart study called KIHD. In 2015 they linked the sauna habits of 2,315 of those men to national death records.1Source 1 · Cohort studyAssociation Between Sauna Bathing and Fatal Cardiovascular and All-Cause Mortality EventsLaukkanen T, Khan H, Zaccardi F, et al.. JAMA Internal Medicine, 2015.Read the paper ↗PubMed ↗ Nearly everyone in the region took saunas. Only 12 men in the whole cohort said they never did, so the study compared men who went once a week with men who went more often.

Over a median of 20.7 years, 49% of the once-a-week men died, against 38% of the men who went two or three times a week and 31% of those who went four to seven times.1Source 1 · Cohort studyAssociation Between Sauna Bathing and Fatal Cardiovascular and All-Cause Mortality EventsLaukkanen T, Khan H, Zaccardi F, et al.. JAMA Internal Medicine, 2015.Read the paper ↗PubMed ↗ The researchers adjusted for age, fitness, smoking, blood pressure, cholesterol, alcohol, diabetes and socioeconomic status. After that, the most frequent bathers had a hazard of death 40% lower than weekly bathers and a hazard of fatal cardiovascular disease 50% lower.

Later papers on the same men cut the groups differently and followed them for longer. With deaths counted through 2018, men who went three to seven times a week had a 14% lower hazard than men who went twice or less.2Source 2 · Cohort studyInflammation, sauna bathing, and all-cause mortality in middle-aged and older Finnish men: a cohort studyKunutsor SK, Jae SY, Kurl S, et al.. European Journal of Epidemiology, 2022.Read the paper ↗PubMed ↗ Among the fitter half of the cohort, frequent sauna use showed no clear link with death from any cause, while fitness itself predicted survival far more strongly.3Source 3 · Cohort studyJoint associations of sauna bathing and cardiorespiratory fitness on cardiovascular and all-cause mortality risk: a long-term prospective cohort studyKunutsor SK, Khan H, Laukkanen T, et al.. Annals of Medicine, 2018.Read the paper ↗PubMed ↗

Women joined the study at a 1998 to 2001 examination. In that sample the link with fewer heart deaths came from the men. Two or three sessions a week made no difference for women compared with one, and the 73 women who went four to seven times had no heart deaths at all.4Source 4 · Cohort studySauna bathing is associated with reduced cardiovascular mortality and improves risk prediction in men and women: a prospective cohort studyLaukkanen T, Kunutsor SK, Khan H, et al.. BMC Medicine, 2018.Read the paper ↗PubMed ↗ That left too few events to estimate their risk.

The closest evidence from outside Finland comes from Japan, where 30,076 adults were followed for about 20 years. People who soaked in a hot tub almost every day had a 28% lower rate of heart disease and stroke than people who bathed twice a week or less.5Source 5 · Cohort studyHabitual tub bathing and risks of incident coronary heart disease and strokeUkai T, Iso H, Yamagishi K, et al.. Heart, 2020.Read the paper ↗PubMed ↗ A Japanese tub runs at around 40°C, so the result speaks to regular heat in general more than to saunas.