Sauna and fitness: what a joint analysis found
Being fit and using the sauna often were each linked to lower mortality in a long Finnish study, and men with both had the lowest rates of all. Here’s what that comparison can, and can’t, tell us.
The short version
Researchers in the same eastern Finland cohort as our heart-health article measured cardiorespiratory fitness directly and asked how often 2,277 men used a sauna, then tracked deaths for a median of 26.1 years. Men with both high fitness and frequent sauna use had the lowest death rates in this group. But high fitness alone came with a somewhat higher rate too, and the groups’ confidence intervals overlap. The comparison cannot show that sauna adds a separate benefit once fitness is accounted for, and nobody’s habits were changed for the study.
Keep in mind
An observational comparison of groups, not a test of whether sauna adds a benefit beyond fitness. The “combined” group’s death rates overlapped closely with the high-fitness group alone.
What they found
Men high in both fitness and sauna frequency had the lowest cardiovascular and all-cause death rates of the four groups: hazard ratios of 0.42 (95% CI 0.28–0.62) for cardiovascular mortality and 0.60 (0.48–0.76) for death from any cause, compared with men low on both.
Men with high fitness but low sauna frequency had similar rates: 0.50 (0.39–0.63) and 0.63 (0.54–0.74). Men with low fitness but high sauna frequency had smaller differences: 0.72 (0.54–0.97) and 0.78 (0.64–0.96).
In plain terms, fitness was linked to a bigger difference in this comparison than sauna frequency was, and the “both high” group’s confidence intervals overlap substantially with the “high fitness only” group. The study did not report a formal statistical test of whether the two factors added up to more than their separate effects.
What this means for your practice
This is a reason to see sauna and exercise as separate, both-worthwhile habits rather than one replacing the other. It is not evidence that adding sauna sessions multiplies the benefit of being fit.
This does not establish a sauna routine to follow, or a target fitness level, and it is not evidence for the effects of any particular KUUME ritual.
Methods and limitations
What the researchers did
This analysis uses the same eastern Finland cohort as our heart-health article, this time in 2,277 men who had a cardiorespiratory fitness test at baseline as well as reporting their sauna habits. Deaths were tracked through national registers for a median of 26.1 years.
The researchers split the men into high or low cardiorespiratory fitness (from an exercise test, split at the group’s midpoint) and high or low sauna frequency (three to seven sessions a week counted as high, two or fewer as low), then compared all four combinations against men who were low on both.
This is observational: nobody’s fitness or sauna habits were assigned or changed for the study.
How much can this tell us?
The study measured fitness directly, with an exercise test, which is a real strength over relying on self-reported activity. But it is still observational, and it is the same men as our heart-health article, sharing the same strengths and limitations.
The four comparison groups are of different sizes, and the confidence intervals for the “both high” and “high fitness only” groups overlap a great deal. That makes it hard to say sauna adds a distinguishable benefit on top of fitness from this comparison alone, even though the point estimate is lowest for the combined group.
Only men took part, both measurements were taken once, and men who were both fit and frequent sauna users may have differed from others in ways the statistics could not fully capture.
What makes it useful
- Fitness measured directly with an exercise test, not self-report
- A long follow-up: a median of 26.1 years
- Compares four combinations of fitness and sauna habits
What limits it
- Observational: cannot show sauna adds a benefit beyond fitness
- The same men as our heart-health article
- Confidence intervals for the top two groups overlap substantially
- Only men, and both habits measured once, at the start
Where this study fits
Where this study fits
We score claims, not single studies. This one is part of the evidence for:
Regular sauna helps you live longer. Some support
Low certaintySmall effectIllness and death
Death from any cause, frequent sauna with low fitness 22% fewer
Likely 4% to 36%
Fewer cases than the comparison group. The bar is the best estimate, the band behind it the likely range.
Sauna can stand in for exercise. Not supported
Low certaintyNo effect foundIllness and death
From the same participant group as 7 other articles in The Study, so we count them as one group of people.
Read the original
Kunutsor 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. Ann Med. 2018;50(2):139-146.
DOI 10.1080/07853890.2017.1387927 · PubMed 28972808