“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 in eastern Finland. Researchers there followed 2,315 middle-aged men 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. So did 24 of the 201 men who went four to seven times a week. That's about 12% of the frequent bathers, compared with 22% of the weekly ones.

The researchers adjusted for age, fitness, smoking, blood pressure, cholesterol, alcohol and socioeconomic status, among other factors. After that, the most frequent bathers had a 50% lower hazard of fatal cardiovascular disease than weekly bathers and a 48% lower hazard of fatal coronary heart disease.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 (a ratio of 1 means no difference), though only 10 men in the top group died that way.

Later papers split the same men into different groups and followed them for longer. One counted deaths through 2014 and drew the line at three sessions a week. In that paper, frequent bathers had a 26% lower hazard of cardiovascular death, and men with high measured fitness had a 49% lower one.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 men, sauna frequency showed no clear link. A 2023 analysis followed the men to 2018. Those who went twice a week or less had a 24% higher hazard of cardiovascular death than 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 an examination that ran from 1998 to 2001. Among women, the hazard ratio for cardiovascular death at two or three sessions a week against one was 1.00, so the extra sessions made no difference. With no cardiovascular deaths among the 73 women in the top group, there was 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. Researchers there followed 30,076 adults 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 says more about regular heat than about saunas.