“Using a sauna four to seven times a week halves your risk of dying from heart disease.”

The research found this

The halving comes from the Kuopio Ischaemic Heart Disease study, which followed 2,315 middle-aged men from eastern Finland for a median of 20.7 years.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 ↗ Of the 601 men who took one sauna a week, 134 died of heart or blood vessel disease. Among the 201 men who went four to seven times a week, 24 did, which works out to about 12% against 22%.

The researchers adjusted for age, fitness, smoking, blood pressure, cholesterol, alcohol and socioeconomic status, among other factors. The most frequent bathers then had a hazard of fatal cardiovascular disease 50% lower than weekly bathers and a hazard of fatal coronary heart disease 48% lower.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 ↗ Sudden cardiac death had the lowest hazard ratio of all at 0.37, though only 10 men in the top group died that way.

Later papers cut the same cohort differently and followed it for longer. With deaths counted to 2014 and the men split at three sessions a week, frequent bathers had a 26% lower hazard of cardiovascular death, while high measured fitness went with a 49% lower hazard.2Source 2 · 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 ↗ Among the fitter half of the cohort, sauna frequency no longer showed a clear link. A 2023 analysis that ran to 2018 found a 24% higher hazard of cardiovascular death in men who went twice a week or less than in men who went three to seven times.3Source 3 · Cohort studyThe Interplay between Systolic Blood Pressure, Sauna Bathing, and Cardiovascular Mortality in Middle-Aged and Older Finnish Men: A Cohort StudyLaukkanen JA, Jae S, Kauhanen J, et al.. The Journal of nutrition, health and aging, 2023.Read the paper ↗PubMed ↗

Women joined the study at a 1998 to 2001 examination. Among women, two or three sessions a week carried a hazard ratio of 1.00 for cardiovascular death against one session, and none of the 73 women in the top group died of cardiovascular disease, which left nothing to estimate.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 ↗

Outside Finland, the closest evidence comes from Japan. Among 30,076 adults followed from 1990 to 2009, people who took a hot bath almost every day had a 35% lower hazard of coronary heart disease 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 ↗ Japanese baths typically run at 40–42°C, so the result speaks to regular heat more than to saunas.