Background: Regular heat exposure is gaining recognition as a potential lifestyle intervention to improve cardiovascular health. Observational data from Finnish and Japanese cohort studies show that frequent sauna use or hot water bathing is associated with a significantly lower risk of cardiovascular events and mortality. These associations remained robust after adjustment for confounders and included adults with cardiovascular risk factors, including type 2 diabetes. While these findings support a potential cardioprotective role for heat therapy, causal relationships have yet to be confirmed. The leading hypothesis is that regular heat exposure enhances vascular health, but this remains to be validated in clinical populations through well-controlled trials.
Objective: This work provides an overview of two studies testing the hypothesis that passive heat exposure improves markers of macrovascular and microvascular function, as well as blood pressure, in adults with either stable coronary artery disease (Study 1) or type 2 diabetes (Study 2).
Methods: In study 1, 41 adults (62 ± 6 years, 29.0 ± 4.3 kg/m2, 33 men/8 women) with stable coronary artery disease were randomized to 8 weeks of Finnish sauna use (n=21, 4 sessions/week, 20-30 min/session) or control intervention (lifestyle maintenance, n=20). In study 2, 18 adults (66 ± 9 years, 28.2 ± 5.4 kg/m2, 11men / 7women) living with type 2 diabetes were randomized to a 12-week home-based heat therapy (leg immersion in 42°C water, n=10) or sham (leg immersion in 36°C water, n=8) intervention (3-5/week, 45-60min/session). In both studies, peripheral endothelial function (brachial artery flow-mediated dilation, baFMD), microvascular reactivity (post-occlusive reactive hyperemia), and blood pressure, were measured before and after the intervention.
Results: In Study 1, no significant differences were observed between interventions for changes in baFMD ( p for interaction = 0.82), systolic (p = 0.951), or diastolic (p = 0.292) blood pressure. However, changes in total (p = 0.031) and peak (p = 0.024) reactive hyperemia differed between interventions, driven by a nonsignificant decrease following sauna use and an increase in the control group. In Study 2, preliminary findings indicate that baFMD increased by 1.50% [95% CI: 0.39; 2.62] with heat therapy, compared to 0.16% [–1.08; 1.41] with the sham intervention. Changes in peak and total reactive hyperemia and in blood pressure did not differ between groups.
Conclusion: These results show that 8 weeks of Finnish sauna bathing did not improve markers of endothelial function, microvascular function or blood pressure in older adults with stable coronary artery disease (study 1). In contrast, preliminary results suggest that 12 weeks of home-based lower leg hot water immersion may improve endothelial function in adults with type 2 diabetes (study 2).
Significance: This project may identify a novel lifestyle intervention that improves markers of vascular health in adults living with type 2 diabetes.