Sixty-minute inhalation of molecular hydrogen decreases blood oxygen saturation but does not alter autonomic cardiac regulation at rest in healthy females: a randomized, double-blind, placebo-controlled crossover study.

Abstract

This randomized, double-blind, placebo-controlled crossover study enrolled 20 physically active healthy females (mean age 22.1 ± 1.6 years) to examine how 60 minutes of molecular hydrogen inhalation affects blood oxygen saturation (SpO2) and heart rate variability (HRV) under resting conditions. Participants completed two sessions—hydrogen or ambient air placebo—separated by a 7-day washout. Continuous monitoring over the 60-minute inhalation period revealed a statistically significant reduction in SpO2 in the hydrogen condition (95.9 ± 1.0%) relative to placebo (96.7 ± 0.7%; p ≤ 0.007); however, this difference was judged to lack clinical relevance. Neither time-domain nor frequency-domain HRV indices showed significant between-condition differences (all p ≥ 0.32). The data indicate that resting autonomic cardiac regulation is unaffected by hydrogen inhalation and that the modest SpO2 decline does not disrupt homeostatic stability.

Mechanism

Dilution of inspired oxygen partial pressure by hydrogen gas may account for the modest SpO2 decline observed; no direct effect on autonomic nervous system activity was detected under resting conditions.