Sauna and Cardiovascular Mortality: The Kuopio Ischemic Heart Disease Risk Factor Study
This is an excerpt from a piece that was written to be persuasive, but more covertly compared to the next piece on neurodegenerative disease.
Cardiovascular disease remains the leading cause of death worldwide, accounting for approximately one in four deaths in the United States. Despite advances in pharmacologic and interventional therapies, population-level prevention strategies capable of meaningfully reducing cardiovascular mortality remain limited. Emerging epidemiologic data suggest that regular sauna use may represent a significant, non-pharmacologic intervention associated with improved cardiovascular outcomes.
The Kuopio Ischemic Heart Disease Risk Factor Study
The relationship between regular sauna use and cardiovascular health was systematically evaluated using data from the Kuopio Ischemic Heart Disease Risk Factor Study (KIHD), a prospective, population-based cohort study conducted in eastern Finland. Initiated in 1984, this ongoing epidemiological study has followed nearly 3,000 middle-aged Finnish men and women over multiple decades to identify risk factors for cardiovascular disease and other age-related conditions.¹
Finland is particularly well suited to this study design due to comprehensive national health registers and the use of a personal identification code assigned to citizens at birth. It is also uniquely suited to studying long-term sauna use, as saunas are an integral part of Finnish culture. There are nearly as many saunas in Finland as there are people—approximately 3.3 million saunas for a population of 5.5 million.
Study Design and Population
The KIHD study enrolled participants aged 42–60 years at baseline, collecting comprehensive data on lifestyle factors, health behaviors, and physiological parameters. Sauna use frequency and duration were assessed at baseline. Participants were stratified into three groups based on frequency: infrequent users (≤1 session per week), moderate users (2–3 sessions per week), and frequent users (≥4 sessions per week). Participants were followed for over 20 years, allowing for long-term outcome assessment.
Cardiovascular Mortality Outcomes
Researchers found substantial differences in cardiovascular outcomes across sauna-use categories. In an initial cohort of 2,315 men, frequent sauna users had a 63% lower risk of fatal cardiovascular events compared to infrequent users (hazard ratio [HR] 0.37, 95% CI 0.18–0.75). All-cause mortality was reduced by 38% in the frequent user group (HR 0.62, 95% CI 0.43–0.90).⁴
In a subsequent cohort including both men and women, frequent sauna users demonstrated a 64% reduction in cardiovascular mortality. When analyzed by total sauna duration rather than frequency, participants reporting more than 45 minutes per week had a 43% lower cardiovascular mortality risk compared to those spending less than 15 minutes weekly, supporting the findings through a different exposure metric.⁵
Comparison with Cardiorespiratory Fitness
To put the magnitude of this effect into context, researchers compared sauna use with cardiorespiratory fitness (CRF), one of the strongest known predictors of cardiovascular health. Participants were categorized into high and low CRF groups based on measured maximal oxygen uptake (VO₂ max).
After 26 years of follow-up, participants with high CRF had a 52% lower incidence of sudden cardiac death compared to those with low CRF. When sauna use was similarly divided into high-frequency (≥3 sessions per week) and low-frequency (0–2 sessions per week) groups, frequent sauna users had a 33% lower risk of sudden cardiac death.⁶
Participants who had both high CRF and frequent sauna use experienced a 69% lower incidence of sudden cardiac death compared to those low in both factors.⁶ This risk reduction exceeded that of either factor alone, suggesting additive cardioprotective effects.
The finding that frequent sauna use is associated with reductions in cardiac mortality comparable to those seen with cardiorespiratory fitness suggests a potential role for sauna use in individuals who wish to improve cardiovascular health but may have limited ability to exercise due to musculoskeletal, respiratory, or other health conditions.
Implications
These findings are compelling. It must be considered that this is a non-randomized, observational cohort study, and thus vulnerable to confounding factors. While the authors did report controlling for potentially confounding variables, cohorts are partticularly vulnerable to these. Also that habits may also change over decades of follow-up, and, the homogeneous Finnish population and cultural context may limit generalizability to populations where sauna use is less prevalent or practiced differently. Randomized controlled trials would be required to establish causality and determine optimal protocols.
Despite these limitations, the study demonstrates substantial reductions in cardiovascular and all-cause mortality associated with sauna use, comparable to the protection seen with cardiorespiratory fitness. The biological mechanisms underlying the associations are well described: heat exposure improves endothelial function, reduces arterial stiffness, enhances autonomic regulation, and decreases inflammation. These mechanisms and the results found support sauna use as a potential adjunctive strategy for cardiovascular risk reduction, particularly in individuals who have limited ability to exercise due to musculoskeletal, respiratory, or other health conditions.
