Non-acute effects of passive heating interventions on cardiometabolic risk and vascular health: systematic review and meta-analysis of randomized controlled trials.

BACKGROUNDS: Passive heating practices, such as hot water immersion and Finnish sauna bathing, have been associated with reduced cardiovascular disease (CVD) risk in observational studies. This systematic review and meta-analysis aimed to comprehensively evaluate the present literature about non-acute effects of passive heating interventions on cardiometabolic and vascular health in randomized controlled trials (RCTs). METHODS AND RESULTS: A comprehensive search was conducted in PubMed, Embase, and Cochrane Central Register of Controlled Trials up to November 4, 2024. We included RCTs that assessed the effects of passive heating interventions of at least one week duration on cardiometabolic and vascular outcomes in adults. Twenty RCTs that tested interventions such as hot water bathing, saunas, hot yoga, and local heating were included in the present review, with durations ranging from 2 to 15 weeks. Our analysis found no significant pooled effects for majority of outcomes, including flow-mediated dilation, pulse wave velocity, resting heart rate, heart rate variability, fasting glucose, HbA1c, total/HDL/LDL cholesterol, triglycerides, and C-reactive protein. For systolic blood pressure (SBP), the overall pooled estimate was not statistically significant (-2.46 mmHg [95 % CI: 5.02 to 0.10]; I²=60.3 %). However, subgroup analyses indicated a significant SBP reduction was confined to systemic (whole-body) heating interventions (-4.11 mmHg [-7.36, -0.86]) and in populations with underlying coronary risk or CVD (-2.52 mmHg [-4.26, -0.79]). CONCLUSIONS: Current evidence from RCTs indicates that passive heating interventions may not improve most of the cardiometabolic or vascular health markers. While a potential reduction in SBP was observed with systemic heating and among adults with coronary risk, this finding should be interpreted with caution due to high heterogeneity and limitations in the included studies.This systematic review is registered at PROSPERO (registration number: CRD42024621600).