Does Heat Thermotherapy Improve Cardiovascular and Cardiometabolic Health? A Systematic Review and Narrative Synthesis of the Literature

Objective: To assess the efficacy of heat thermotherapy to improve cardiovascular and cardiometabolic health, and to compare potential heat thermotherapy moderating factors. Design: Systematic review and narrative synthesis. Data Sources Electronic databases (MEDLINE, EMBASE and Web of Science) were searched up to 6th February 2020. Eligibility criteria for selecting studies Journal articles with adult participants, a controlled trial study design, and a passive heating stimulus with a cardiovascular or cardiometabolic health outcome were included. Results: From 1036 articles, 39 articles met the inclusion criteria. Heat thermotherapy was delivered acutely (one bout; n=19), short term (2-15 bouts; n=6) and chronically (>15 bouts; n=14), via either hot water immersion (n=26; water temperature 38-43 °C) or heated air exposure (n=11; air temperature 31-90 °C), or water perfused suit/handheld device (n=2). Heat exposure ranged from 10 to 240 minutes. Cardiovascular and cardiometabolic measurement techniques varied across studies, alongside participant age (≤35 years, n=376; >35 ≤60 years, n=335 and >60 years, n=350) and health status. 21/27 studies measuring cardiovascular outcomes reported positive health benefits, including increased flow-mediated dilation (1.3-5.3%) and lower systolic blood pressure (4-16 mm Hg). 15/22 studies measuring cardiometabolic outcomes reported positive health benefits, including reduced postprandial glucose (-0.89 to -0.5 mmol.L -1 ) and C-reactive protein concentrations (-0.9 to -10.94 mg.L -1 ). Conclusion: Overall, 29/39 studies demonstrated significant positive cardiovascular or cardiometabolic health benefits from heat thermotherapy across various population demographics, despite varied study design and modality. Heat thermotherapy is an efficacious treatment for cardiovascular disease alongside pharmaceutical and exercise-based interventions.