Combined Effect of Sauna Bathing and Cardiorespiratory Fitness on the Risk of Sudden Cardiac Deaths in Caucasian Men: A Long-term Prospective Cohort Study

Abstract

Both cardiorespiratory fitness (CRF) and frequency of sauna bathing (FSB) are each strongly and independently associated with sudden cardiac death (SCD) risk. However, the combined effect of CRF and FSB on SCD risk has not been previously investigated. We evaluated the joint impact of CRF and FSB on the risk of SCD in the Kuopio Ischemic Heart Disease prospective cohort study of 2291 men aged 42-61 years at recruitment. Objectively measured CRF and self-reported sauna bathing habits were assessed at baseline. CRF was categorized as low and high (median cutoffs) and FSB as low and high (defined as ≤2 and 3-7 sessions/week respectively). Multivariable adjusted hazard ratios (HRs) with confidence intervals (CIs) were calculated for SCD. During a median follow-up of 26.1 years, 226 SCDs occurred. Comparing high vs low CRF, the HR (95% CIs) for SCD in analysis adjusted for several established risk factors was 0.48 (0.34-0.67). Comparing high vs low FSB, the corresponding HR was 0.67 (0.46-0.98). Compared to men with low CRF & low FSB, the multivariate-adjusted HRs of SCD for the following groups: high CRF & high FSB; high CRF & low FSB; and low CRF & high FSB were 0.31 (0.16-0.63), 0.49 (0.34-0.70), and 0.71 (0.45-1.10) respectively. In a general male Caucasian population, the combined effect of high aerobic fitness (as measured by CRF) and frequent sauna baths is associated with a substantially lowered risk of future SCD compared with high CRF or frequent sauna bathing alone.

Cardiovascular and Other Health Benefits of Sauna Bathing: A Review of the Evidence

“…Furthermore, our recent research evidence suggests that a combination of regular physical activity and sauna baths is associated with a substantial reduction in the risk of fatal cardiovascular and all-cause mortality events compared with each modality alone. 5,19 Our findings indicate that physical activity and sauna bathing each have independent effects on vascular disease, suggesting the likelihood that the recent finding on the beneficial effects of sauna bathing on CVD is not due to physical activity or exercise. Despite the several limitations of previous study designs, the preceding evidence may be translated into clinical improvements.…”

“…In 2 recent studies in the general Finnish male population, the combined effect of high CRF level and frequent sauna baths was found to be associated with a substantially reduced risk of future cardiovascular deaths, SCD, and allcause mortality outcomes in comparison to high CRF level or frequent sauna baths alone. 5,19 These recent findings have practical implications, which indicate that high CRF levels, which can usually be improved by regular physical activity, when combined with frequent sauna bathing sessions, can substantially reduce the risk of these adverse cardiovascular outcomes. Evidence from well-designed intervention studies are needed to confirm whether the associations between high CRF levels, sauna bathing, and CVD outcomes are causal.…”

“…Indeed, we have recently shown that a combination of good fitness levels due to aerobic exercise and frequent sauna bathing confers more protection against the risk of cardiovascular and all-cause mortality events. 5,19 Further evidence is needed to find the mechanistic pathways linking sauna exposure and its effect on nonfatal and fatal or intermediate cardiovascular outcomes as well as other health conditions with subclinical outcomes such as arterial wall changes, especially in general populations.…”

Sauna bathing is associated with reduced cardiovascular mortality and improves risk prediction in men and women: a prospective cohort study

“…Though there is a possibility that factors such as physical activity could potentially explain these finding, it is unlikely as our analysis accounted for the role of physical activity. Furthermore, our recent research evidence suggests that a combination of regular physical fitness and sauna baths is associated with a substantial reduction in the risk of fatal cardiovascular and all-cause mortality events compared with each modality alone [ 57 , 58 ]. We have shown that even participants with low fitness levels have a reduced risk of mortality when combined with frequent (3–7 sessions per week) or infrequent (≤ 2 sessions per week) sauna use.…”

Cardiorespiratory Fitness and the Risk of Serious Ventricular Arrhythmias: A Prospective Cohort Study

“…Major CVD risk factors for SCD, such as hypertension, smoking, obesity, and diabetes are also arrhythmogenic substrates. 12 Given that CHD, SCD and VAs have shared risk factors and with the established relationship between CRF and these outcomes (CHD and SCD), 13,14 we hypothesized that CRF would be linked to the risk of VAs. Despite acute coronary artery occlusion being the main trigger for VAs, 12 the pathogenesis of VAs is still poorly understood.…”