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

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. (C) 2019 Elsevier Ltd. All rights reserved.