Hydrogen-rich water has a positive effect on heart rate variability at rest and during orthostatic loading, but not during cycling, in healthy adults: A pilot randomized, placebo-controlled crossover trial

Hydrogen-rich water has various health benefits, such as substantially reducing lactate accumulation during high-intensity exercise. However, little is known about the effects of hydrogen-rich water on physiological responses during physical activity compared to those at rest. Therefore, we investigated the short-term effects of hydrogen-rich water on autonomic nervous system activity under static and orthostatic conditions and physiological responses during exercise. This was a double-blind, randomized, placebo-controlled crossover study (UMIN000050872). Fifty healthy adults with different fitness levels were recruited. The intervention involved the intake of hydrogen-rich water. Participants were randomly assigned (1:1) into two groups: one was administered hydrogen-rich water first, and the other was administered placebo water first. Participants consumed 290 mL of hydrogen-rich water or placebo water three times: the day before, 90 min before, and immediately before the two tests: heart rate variability test under static and orthostatic conditions, followed by a 30 min constant cycling test at 115% of the anaerobic threshold. Among all recruited participants, three individuals were excluded because of scheduling conflicts or incomplete measurement data, resulting in 47 participants (34 women, mean age 46.7 ± 10.3 years, peak VO2 22.5 ± 4.0 mL/kg/min). Hydrogen-rich water significantly increased the high-frequency, low-frequency, and coefficient of variation of the R-R interval at rest (p < 0.05). Additionally, hydrogen-rich water maintained a high coefficient of variation in the R-R interval and low frequency even in the early phase of orthostatic stress. In contrast, hydrogen-rich water had no significant effect on heart rate, blood lactate, or VO2 during exercise compared to placebo water. In conclusion, hydrogen-rich water enhanced autonomic function during orthostatic stress and at rest. This favorable effect was observed after a few intakes of hydrogen-rich water.