Laukkanen et al. 2018, Sauna and cardiovascular mortality

Finnish prospective cohort (KIHD). More frequent sauna bathing was associated with lower cardiovascular mortality in a dose-dependent pattern: 4-7 sessions per week carried about 50% lower cardiovascular mortality than one session per week. Observational, mostly Finnish men with a lifelong sauna culture, so confounding and limited generalisability apply. This is a health-association signal, not a performance or recovery finding. Limited for causation.