Sauna bathing, renal function and chronic kidney disease: Cross-sectional and longitudinal findings from the KIHD study.

BACKGROUND: It is uncertain if passive heat therapies are associated with adverse renal outcomes. We sought to evaluate the cross-sectional and longitudinal associations of the frequency of sauna bathing with renal function measures and chronic kidney disease (CKD). MATERIALS AND METHODS: Baseline self-reported sauna bathing habits were assessed in 2071 men aged 42-61 years with normal kidney function. Baseline estimated glomerular filtration rate (GFR) and serum levels of creatinine, potassium (K) and sodium (Na) were measured, with only 11-year measurements of K and Na 11 years in a random subset of participants due to logistical reasons. Study participants were followed up for CKD diagnosed using KDOQI guidelines, which were collected from the National Hospital Discharge Registry. The associations of frequency of sauna bathing with renal function measures were evaluated using regression analyses. Hazard ratios (HRs; 95% CIs) were estimated for CKD. RESULTS: There were no significant changes in baseline levels of estimated GFR, creatinine and Na comparing 4-7 sauna sessions/week versus 1 sauna session/week; there was a slight increase in K .05 mmoL/L (95% CI, .00, .10; p = .033). There were no significant changes in levels of serum K and Na at 11 years. After 25.7 years overall median follow-up, 188 CKD cases were recorded. Comparing 4-7 sauna sessions/week with 1 sauna session/week, there was no evidence of an association with CKD .84 (95% CI, .46-1.53; p = .56). CONCLUSIONS: Cross-sectional and longitudinal observational evidence suggests that frequent sauna bathing is not associated with impaired renal function or the future risk of CKD.