Longitudinal associations of sauna bathing with inflammation and oxidative stress: the KIHD prospective cohort study

Purpose: We sought to determine cross-sectional and longitudinal associations of frequency of sauna bathing with high sensitivity C-reactive protein (hsCRP), fibrinogen, leucocyte count and gamma-glutamyltransferase (GGT).Design: Baseline sauna bathing habits were assessed in 2269 men aged 42-61 years. Concentrations of hsCRP, fibrinogen, leucocyte count, and GGT were determined at baseline and 11 years later. The associations of sauna bathing frequency with baseline and 11-year hsCRP, fibrinogen, leucocyte count, and GGT levels were examined using robust multivariate regression analyses.Results: In baseline analysis, 4-7 sauna sessions/week (compared with 1 sauna session/week) was associated with -0.84mg/l (95% CI, -1.55, -0.14; p=.019) lower hsCRP; -0.07g/l (95% CI, -0.15, 0.02; p=.112) lower fibrinogen; and -0.28x10(9)/l (95% CI, -0.51, -0.06; p=.015) lower leucocyte count, after multivariable adjustment. In longitudinal analysis, the corresponding estimates were -1.66mg/l (95% CI, -3.13, -0.19; p=.027); -0.16g/l (95% CI, -0.31, -0.02; p=.031); and -0.49x10(9)/l (95% CI, -0.85, -0.14; p=.007) respectively. Sauna bathing frequency was not associated with GGT at baseline and 11 years.Conclusion: Observational evidence supports the hypothesis that reduction in inflammation may be one of the pathways linking frequent sauna bathing with decreased risk of acute and chronic disease conditions.KEY MESSAGESCross-sectional evidence or short-term studies suggest Finnish sauna bathing may exert its beneficial health effects via reduction in inflammation and oxidative stress; however, the long-term effects of sauna bathing on these outcomes are uncertain.In this population-based prospective cohort study, frequent sauna sessions significantly decreased levels of inflammatory markers at baseline and 11-year follow-up; but had no effect on oxidative stress.The health benefits of sauna bathing may in part be mediated via reduced systemic inflammation.