Heat-retention effects of hydrogen-rich water bath assessed by thermography for humans.

Abstract

A thermographic clinical trial involving 24 healthy participants compared heat retention after hydrogen-rich water bathing (hydrogen concentration 185–548 μg/L; oxidation-reduction potential −167 to −91 mV) versus ordinary water bathing under identical conditions (41°C, 10 minutes). Infrared imaging at 30 and 60 minutes post-bath revealed greater surface temperature maintenance in the hydrogen-rich group across multiple body regions, ranked in descending order: abdomen, upper legs, arms, hands, and feet. Fingertip capillary thickness measurements indicated vascular dilation was more pronounced after hydrogen-rich bathing, pointing to a circulatory-promoting effect beyond simple thermal retention. Heat retention showed weak-to-moderate positive correlations with subcutaneous fat, total body fat, and BMI, and an inverse correlation with skeletal muscle ratio, while basal metabolic rate showed little association. These findings suggest hydrogen-rich water bathing enhances post-bath warmth across diverse body regions through blood flow promotion reflected by capillary expansion.

Mechanism

Hydrogen-rich water bathing appears to dilate peripheral capillaries and enhance blood circulation, producing post-bath heat retention that exceeds what thermal effects alone would predict.