Joint associations of sauna bathing and cardiorespiratory fitness on cardiovascular and all-cause mortality risk: a long-term prospective cohort study

PURPOSE: We aimed to evaluate the joint impact of cardiorespiratory fitness (CRF) and frequency of sauna bathing (FSB) on the risk of cardiovascular and all-cause mortality.

DESIGN: CRF measured by respiratory gas analyses and sauna exposure were assessed at baseline in a prospective study of 2,277 men. CRF was categorized as low and high (median cutoffs) and FSB as low and high (≤ 2 and 3-7 sessions/week respectively).

RESULTS: During a median follow-up of 26.1 years, 520 cardiovascular and 1,124 all-cause deaths occurred. Comparing high vs low CRF, the multivariate-adjusted hazard ratios (HRs) 95% CIs for cardiovascular and all-cause mortality were 0.51 (0.41-0.63) and 0.65 (0.57-0.75) respectively. Comparing high vs low FSB, the corresponding HRs were 0.74 (0.59-0.94) and 0.84 (0.72-0.97) respectively. Compared to low CRF & low FSB, the HRs of CVD mortality for high CRF & high FSB; high CRF & low FSB; and low CRF & high FSB were 0.42 (0.28-0.62), 0.50 (0.39-0.63), and 0.72 (0.54-0.97) respectively. For all-cause mortality, the corresponding HRs were 0.60 (0.48-0.76), 0.63 (0.54-0.74), and 0.78 (0.64-0.96) respectively.

CONCLUSION: A combination of high CRF and frequent sauna bathing confers stronger long-term protection on mortality outcomes compared with high CRF or high FSB alone.