“Regular sauna use helps you live longer.”

The research found this

Between 1984 and 1989, researchers recruited 2,682 men from Kuopio in eastern Finland for a heart study called KIHD. The men were 42 to 60 years old. In 2015 the team linked the sauna habits of 2,315 of them 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, and only 12 men in the whole study 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. The figure was 38% among men who went two or three times a week and 31% among 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 then accounted for age, fitness, smoking, blood pressure, cholesterol, alcohol, diabetes and socioeconomic status. After those adjustments, the most frequent bathers had a 40% lower risk of death than weekly bathers and a 50% lower risk of dying from cardiovascular disease.

Later papers on the same men split 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 risk of death 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 men, frequent sauna use showed no clear link with death from any cause, and 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 an examination round between 1998 and 2001. In that sample, the link with fewer heart deaths came from the men. For women, two or three sessions a week made no difference 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. Researchers there followed 30,076 adults for about 20 years, and 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 finding is about regular heat in general and says less about saunas.