Frequent sauna bathing offsets the increased risk of death due to low socioeconomic status: A prospective cohort study of middle-aged and older men

Background and aim: Low socioeconomic status (SES) and frequent sauna bathing are associated with increased and decreased risk of all-cause mortality, respectively. Whether there is an interplay among SES, sauna bathing and all-cause mortality risk is not known. We aimed to evaluate the separate and joint associations of SES and frequency of sauna bathing (FSB) with all-cause mortality risk in a prospective cohort study. Methods: We employed the Kuopio Ischaemic Heart Disease Study cohort comprising of 2575 men aged 42–61 years at study entry. Self-reported SES and sauna bathing habits were assessed at baseline. Socioeconomic status was categorized as low and high (median cutoff) and FSB as low and high (defined as ≤2 and 3–7 sessions/week, respectively). Results: During a median follow-up of 27.8 years, 1618 deaths occurred. Comparing low vs high SES, the multivariable-adjusted HR (95 % CI) for all-cause mortality was 1.31 (1.18–1.45). Comparing high vs low FSB, the multivariable-adjusted HR (95 % CI) for all-cause mortality was 0.86 (0.76–0.97). Compared with high SES-low FSB, low SES-low FSB was associated with an increased risk of all-cause mortality 1.35 (1.20–1.51), without significant evidence of an association for low SES-high FSB and all-cause mortality risk 1.07 (0.89–1.29). Positive additive and multiplicative interactions were found between SES and FSB. Conclusions: There exists an interplay among SES, sauna bathing and all-cause mortality risk in a general Finnish male population. Frequent sauna baths may offset the increased overall mortality risk due to low SES.