Short read
The Kuopio Ischaemic Heart Disease Risk Factor Study (KIHD) is a prospective cohort in eastern Finland with baseline examinations between 1984 and 1989. Laukkanen and colleagues analysed 2,315 men aged 42 to 60 and followed them for a median of 20.7 years. Sauna habits were grouped by frequency: 601 men went once a week, 1,513 two to three times and 201 four to seven times. Only 12 reported no sauna use at all.
After adjustment for cardiovascular risk factors, men with four to seven sessions a week had a 63 % lower relative risk of sudden cardiac death than men who went once a week, a hazard ratio of 0.37. Against the same once-a-week group, the relative risk was 48 % lower for fatal coronary heart disease, 50 % lower for fatal cardiovascular disease and 40 % lower for death from any cause. Session length was also associated with risk: more than 19 minutes per session compared favourably with less than 11 minutes.
The reference group is the detail most citations drop. Because almost every man in the cohort used the sauna, every figure compares frequent use with weekly use, never with no sauna at all. The study is observational and cannot show cause and effect. It covers only men, only eastern Finland and only the traditional Finnish sauna at around 79 degrees. Three published letters pointed to possible spurious correlation: frequent users may have more free time, less strain and better baseline health.
The direction was consistent across all four endpoints. The authors discuss improved endothelial function, lower blood pressure and a shift in autonomic balance as possible mechanisms. None of this defines a dose for an individual, and the findings do not carry over to women or to other forms of heat without further data.