Fitness predicted Finnish men's survival more strongly than sauna use did
In 2,277 Kuopio men, this 2018 Annals of Medicine paper weighed sauna habits against measured fitness and counted deaths over 26 years.
The paper
Joint associations of sauna bathing and cardiorespiratory fitness on cardiovascular and all-cause mortality risk: a long-term prospective cohort study
Kunutsor SK, Khan H, Laukkanen T, Laukkanen JA. Annals of Medicine, 2018;50(2):139-146.
See the study at a glance
- Design
- Prospective cohort study
- People
- 2,277 men
- Who they were
- Men aged 42 to 61 from the Kuopio study had their fitness measured on an exercise test when they joined in the 1980s.
- What they did
- The researchers compared two or fewer sauna sessions a week with three to seven. For fitness they split the men at the median VO2max of 30.03 mL/kg/min. VO2max is the most oxygen the body can use during hard exercise.
- How long
- Median 26.1 years
These numbers came out of it
0.51
Fitter men had this hazard ratio for cardiovascular death compared with less fit men. It works out to about half the risk.
0.74
Three to seven sauna sessions a week, compared with two or fewer, went with this hazard ratio for cardiovascular death.
0.84
Among the fitter men, frequent sauna use had this hazard ratio, and its plausible range included no effect.
0.42
Men who were both fit and frequent bathers had this hazard ratio for cardiovascular death compared with men who were neither.
Hazard ratio for cardiovascular death with 95% confidence interval
Fit men who also bathed often had the lowest risk of cardiovascular death
The model adjusted for age, body mass index, smoking, systolic blood pressure, total and HDL cholesterol, type 2 diabetes, coronary heart disease, alcohol, socioeconomic status and C-reactive protein (a marker of inflammation). Physical activity doesn't appear in any of the listed models.
The researchers did this
Frequent bathers in Kuopio were fitter than weekly bathers.Source 2 · 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 ↗ That left open whether fitness explained the sauna findings. This paper tested the idea in the 2,277 men whose maximal oxygen uptake had been measured on an exercise test at the start.Source 1 · 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 ↗
Over a median of 26.1 years, 520 men died of cardiovascular disease and 1,124 died of any cause. Compared with twice a week or less, three to seven sauna sessions a week went with a hazard ratio of 0.74 for cardiovascular death. Fitter men had a hazard ratio of 0.51 against less fit men, and the authors concluded that fitness remained the strongest indicator.Source 1 · 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 ↗
A joint analysis compared everyone with men who were less fit and bathed infrequently. Against that group, fitness alone went with a hazard ratio of 0.50 and frequent sauna use alone with 0.72. Men who had both came out at 0.42. Within the fitter half, frequent sauna use showed no clear link with cardiovascular death, and its hazard ratio of 0.84 had a plausible range from 0.56 to 1.27.Source 1 · 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 authors calculated that four men would need to be both fit and frequent bathers over the follow-up to prevent one cardiovascular death. That calculation assumes cause and effect, and a study that watches people over time can't establish it.
The study can't tell you these things
- Sauna habits and fitness were each measured once in the 1980s.
- This paper drew its sauna line at three sessions a week, and the 2015 paper used four, so the two sets of results don't line up exactly.Source 2 · 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 adjustments listed in the paper leave out physical activity.
- Every participant was a man. The Kuopio study's one analysis of heart deaths in women found no link at two or three sessions a week.Source 3 · 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 ↗
People quote it like this
Later reviews by the same group cite the joint result in support of sauna plus exercise.Source 4 · ReviewCardiovascular and Other Health Benefits of Sauna Bathing: A Review of the EvidenceLaukkanen JA, Laukkanen T, Kunutsor SK. Mayo Clinic Proceedings, 2018.Read the paper ↗PubMed ↗Source 5 · ReviewDoes the Combination of Finnish Sauna Bathing and Other Lifestyle Factors Confer Additional Health Benefits? A Review of the EvidenceKunutsor SK, Laukkanen JA. Mayo Clinic Proceedings, 2023.Read the paper ↗PubMed ↗ In the paper's own data, fitness is the stronger predictor, and among fit men sauna frequency showed no clear link.
We cited these sources
- 01Kunutsor SK, Khan H, Laukkanen T, Laukkanen JA. Joint associations of sauna bathing and cardiorespiratory fitness on cardiovascular and all-cause mortality risk: a long-term prospective cohort study. Annals of Medicine. 2018;50(2):139-146. doi:10.1080/07853890.2017.1387927 PMID 28972808
- 02Laukkanen T, Khan H, Zaccardi F, Laukkanen JA. Association Between Sauna Bathing and Fatal Cardiovascular and All-Cause Mortality Events. JAMA Internal Medicine. 2015;175(4):542-548. doi:10.1001/jamainternmed.2014.8187 PMID 25705824
- 03Laukkanen T, Kunutsor SK, Khan H, Willeit P, Zaccardi F, Laukkanen JA. Sauna bathing is associated with reduced cardiovascular mortality and improves risk prediction in men and women: a prospective cohort study. BMC Medicine. 2018;16(1):219. doi:10.1186/s12916-018-1198-0 PMID 30486813
- 04Laukkanen JA, Laukkanen T, Kunutsor SK. Cardiovascular and Other Health Benefits of Sauna Bathing: A Review of the Evidence. Mayo Clinic Proceedings. 2018;93(8):1111-1121. doi:10.1016/j.mayocp.2018.04.008 PMID 30077204
- 05Kunutsor SK, Laukkanen JA. Does the Combination of Finnish Sauna Bathing and Other Lifestyle Factors Confer Additional Health Benefits? A Review of the Evidence. Mayo Clinic Proceedings. 2023;98(6):915-926. doi:10.1016/j.mayocp.2023.01.008 PMID 37270272