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 2277 men. CRF was categorized as low and high (median cut-offs) 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 1124 all-cause deaths occurred. Comparing high versus 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 versus 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.

CONCLUSIONS: 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. KEY MESSAGES Cardiorespiratory fitness (CRF) and frequency of sauna bathing are independently associated with reduced mortality risk; a combination of good CRF and frequent sauna bathing may confer additional survival benefits. In a population-based prospective cohort study, a combination of high CRF levels and frequent sauna bathing (3-7 sessions per week) was associated with a substantial risk reduction in fatal cardiovascular and all-cause mortality events compared with good CRF or frequent sauna bathing alone. A combination of good fitness levels produced by aerobic exercises and frequent sauna bathing may have added health benefits and confer more protection on the risk of mortality.