Story · Heat

Meet the 2,315 Finnish men behind the sauna longevity headlines.

The best-known sauna study followed men from one Finnish town for more than twenty years.Source 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 ↗ Its numbers now turn up on podcasts and on the product pages of sauna brands. Scroll through the cohort one ember at a time to see where they come from.

By Adam BognarSep 24, 20266 min read

Scroll to meet them ↓

Kuopio, 1984

A heart study in eastern Finland asked 2,327 men how often they took a sauna

Researchers recruited middle-aged men from Kuopio and the surrounding countryside between 1984 and 1989, and each man filled in a questionnaire about his sauna habits.Source 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 ↗ Every point of light on this page is one of those men.

The non-users

Twelve men never took saunas, so the study left them out

That left 2,315 men and no comparison group of people who avoid the sauna. Every result from here compares frequent bathers with men who went once a week.Source 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 ↗

Three habits

The men split into three groups by how often they went

601 went once a week and 1,513 went two or three times. The group behind the famous numbers, 201 men, went four to seven times a week.Source 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 ↗

1984 to 2011

The researchers followed every man through national death records

Scroll slowly. Each ember goes out when a man in its group dies.

The totals at the end come from the paper. How the deaths spread across the years is our illustration, because the paper reports only the totals.Source 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 ↗

By 2011

Half the weekly bathers had died, and under a third of the most frequent ones

Deaths ran at 49% in the once-a-week group, 38% in the middle group and 31% in the top group.Source 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 ↗

After adjustment for age, fitness, smoking and socioeconomic status, among other things, the hazard of death in the top group was 40% lower. That figure is the one that reached the headlines.

Before the study began

The most frequent bathers started out healthier

They were younger and fitter than the weekly bathers, and fewer of them smoked: 20% against 36%.Source 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 ↗ Statistical adjustment corrects for the differences a study measures, and a questionnaire from 1984 left plenty unmeasured.

Sudden cardiac death

The famous 63% drop in sudden cardiac death rests on ten men

Ten of the 201 frequent bathers died suddenly of heart problems, against 61 of the 601 weekly bathers. With numbers that small a ratio can swing a long way, which is why its confidence interval runs from 0.18 to 0.75.Source 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 ↗

Fitness

Fit men who rarely took saunas did better than unfit men who went often

A 2018 analysis split 2,291 of the men by measured fitness as well as by sauna habit. Sudden cardiac deaths ran at 5.5% among fitter men who took two or fewer saunas a week, and at 11.0% among less fit men who took three to seven.Source 2 · Cohort studyCombined Effect of Sauna Bathing and Cardiorespiratory Fitness on the Risk of Sudden Cardiac Deaths in Caucasian Men: A Long-term Prospective Cohort StudyLaukkanen JA, Laukkanen T, Khan H, et al.. Progress in Cardiovascular Diseases, 2018.Read the paper ↗PubMed ↗

Once fitness entered the model, the sauna association lost statistical significance.

Followed to 2018

With longer follow-up the gap narrowed to 14%

A 2022 analysis of 2,575 men followed the cohort to 2018 and drew the line at three sessions a week. The frequent group's hazard of death came out 14% lower.Source 3 · 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 ↗

By then 56% of the men who took three to seven saunas a week had died, against 65% of the rest.Source 4 · Cohort studyFrequent sauna bathing offsets the increased risk of death due to low socioeconomic status: A prospective cohort study of middle-aged and older menKunutsor SK, Jae SY, Laukkanen JA. Experimental Gerontology, 2022.Read the paper ↗PubMed ↗

Women

Women joined in 1998, and the link didn't show up for them

In a later sample of 1,688 men and women, the association with fewer heart deaths came from the men. Women who went two or three times a week did no better than women who went once.Source 5 · 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 ↗

The 73 women in the top group had no heart deaths at all, which left too few events to estimate their risk.

The study shows an association in one group of Finnish men

The Finnish men who took the most saunas did die less often, and the association held after the researchers accounted for fitness, smoking, blood pressure and socioeconomic status. It comes from one cohort of middle-aged men. With longer follow-up it shrank, and in the fittest men it disappeared.Source 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 ↗Source 3 · 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 ↗Source 6 · 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 ↗ No trial has tested sauna against death.

Sauna looks like a habit with a plausible upside for the heart. Exercise predicted survival more strongly in the same men.Source 6 · 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 ↗ The numbers behind the other heart claims sit on the claims page.

36°H

Likely

Heat

“Regular sauna use helps you live longer.”

One Finnish cohort ties frequent sauna use to fewer deaths. With longer follow-up the gap shrank from 40% to about 14%, and it disappeared in the fittest men and in women's heart deaths.

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