# Molecular hydrogen inhalation modulates resting metabolism in healthy females: findings from a randomized, double-blind, placebo-controlled crossover study.
> 水素ガス吸入が安静時代謝に与える影響：健康な女性を対象とした無作為化二重盲検プラセボ対照クロスオーバー試験


## Abstract

This randomized, double-blind, placebo-controlled crossover study enrolled 20 physically active healthy females (mean age 22.1 ± 1.6 years) at Palacký University Olomouc between September 2022 and March 2023. Participants inhaled either molecular hydrogen or ambient air via nasal cannula at 300 mL/min for 60 minutes at rest. Indirect calorimetry was used to assess metabolic responses, with breath-by-breath data averaged across four 15-minute intervals. Compared with the placebo condition, hydrogen inhalation produced significant reductions in both the respiratory exchange ratio and ventilation across all intervals. A negative correlation between the change in respiratory exchange ratio and body fat percentage emerged from 30 minutes onward, indicating that individuals with greater adiposity experienced more pronounced increases in fat oxidation during hydrogen inhalation.

### Mechanism

Inhalation of molecular hydrogen reduced the respiratory exchange ratio, indicating a shift toward greater fat oxidation at rest. The magnitude of this metabolic shift correlated negatively with body fat percentage, suggesting that hydrogen's selective antioxidant properties may modulate substrate utilization, particularly in individuals with higher adiposity.

## Bibliographic

- **Authors**: Grepl P, Botek M, Krejčí J, McKune A
- **Journal**: Med Gas Res
- **Year**: 2025 (2025-09-01)
- **PMID**: [39923133](https://pubmed.ncbi.nlm.nih.gov/39923133/)
- **DOI**: [10.4103/mgr.MEDGASRES-D-24-00085](https://doi.org/10.4103/mgr.MEDGASRES-D-24-00085)
- **PMC**: [PMC12054672](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12054672/)
- **Study type**: human randomized controlled trial
- **Delivery route**: inhalation
- **Effect reported**: positive

## Delivery context

For inhalation applications of molecular hydrogen, the lower flammability limit (LFL) deserves careful handling. The classical 4% figure applies to closed-system mixtures; the practical inhalation-environment threshold is 10%. Even pure-hydrogen output (the UFL 75% paradox) passes through the flammable range at the air–gas boundary. High-concentration (66% / 100%) inhalers are documented in the Japanese Consumer Affairs Agency accident-information database and are not recommended.

## Safety notes

For inhalation applications of molecular hydrogen, the lower flammability limit (LFL) deserves careful handling. The classical 4% figure applies to closed-system mixtures; the practical inhalation-environment threshold is 10%. Even pure-hydrogen output (the UFL 75% paradox) passes through the flammable range at the air–gas boundary. High-concentration (66% / 100%) inhalers are documented in the Japanese Consumer Affairs Agency accident-information database and are not recommended.

See also:
- [Inhalation concentration and LFL / UFL](https://h2-papers.org/en/safety-notes/inhalation-concentration)
- [Consumer Affairs Agency accident cases](https://h2-papers.org/en/safety-notes/accident-cases)
- [LFL / UFL terminology](https://h2-papers.org/en/safety-notes/lfl-ufl-explained)
- [Inhalation safety threshold lineage](https://h2-papers.org/en/safety-notes/lineage)

---

> **Cite as**: H2 Papers — PMID 39923133. https://h2-papers.org/en/papers/39923133
> **Source**: PubMed PMID [39923133](https://pubmed.ncbi.nlm.nih.gov/39923133/)