Finnish sauna bathing does not increase or decrease the risk of cancer in men: A prospective cohort study

Abstract Introduction Evidence suggests that heat therapy can be used to prevent and treat cancer; anecdotal reports suggest passive heat therapies may increase cancer risk. Finnish sauna bathing has been linked to a reduced risk of chronic diseases, but its association with cancer risk is unknown. We aimed to assess the prospective association between frequency of sauna bathing and the risk of all-cause and site-specific cancers using the Kuopio Ischemic Heart Disease prospective cohort. Methods Baseline sauna bathing habits were assessed in 2173 men aged 42–61 years with no history of cancer. Hazard ratios (HRs) with 95% confidence intervals (CIs) for cancer were calculated using Cox proportional hazard models. We corrected for within-person variability in sauna bathing habits using data from repeat assessments taken 11 years apart. Results During a median follow-up of 24.3 years, 588 (27.1%) all-cause cancer cases were recorded. The age-adjusted regression dilution ratio of sauna bathing frequency was 0.69 (0.62–0.76). In multivariable-adjusted analyses, the HRs (95% CIs) of all-cause cancer were 0.92 (0.76–1.11) and 0.92 (0.66–1.27) for men who had 2-3 and ≥4 sauna sessions per week, respectively, compared with men who had ≤1 sauna session per week. The non-significant findings were consistent for prostate, gastrointestinal and lung cancers on multivariate adjustment. Conclusion Frequent Finnish sauna bathing is not associated with the risk of cancer in a middle-aged male Caucasian population. Further studies are required to confirm or refute these findings, particularly in women and other age groups.