# Protective effects of hydrogen gas inhalation on radiation-induced bone marrow damage in cancer patients: a retrospective observational study.
> がん患者における放射線誘発性骨髄障害に対する水素ガス吸入の保護効果：後ろ向き観察研究


## Abstract

This retrospective observational study investigated whether 5% H2 gas inhalation for 30 minutes following each session of intensity-modulated radiation therapy (IMRT) could reduce bone marrow damage in cancer patients. Patients in the control group (n=7) received mild hyperbaric oxygen after IMRT, while those in the hydrogen group (n=16) inhaled 5% H2 gas. Peripheral blood analysis showed that white blood cell and platelet counts declined significantly in the control group, whereas the hydrogen group exhibited significantly attenuated reductions in both parameters (P=0.0011 and P=0.0275, respectively). Red blood cell counts, hemoglobin, and hematocrit were unaffected in both groups. Importantly, anti-tumor efficacy of IMRT was comparable between groups, suggesting that H2 inhalation did not interfere with radiation's therapeutic action while offering hematoprotective benefits.

### Mechanism

Molecular hydrogen is proposed to selectively neutralize hydroxyl radicals (·OH) and peroxynitrite (ONOO⁻) generated during radiation exposure, thereby reducing oxidative damage to bone marrow cells without impairing the ionizing effects on tumor tissue.

## Bibliographic

- **Authors**: Hirano S, Aoki Y, Li XM, Ichimaru N, Takahara S, Takefuji Y
- **Journal**: Med Gas Res
- **Year**: 2021
- **PMID**: [33942780](https://pubmed.ncbi.nlm.nih.gov/33942780/)
- **DOI**: [10.4103/2045-9912.314329](https://doi.org/10.4103/2045-9912.314329)
- **PMC**: [PMC8174412](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8174412/)
- **Study type**: human observational study
- **Delivery route**: inhalation
- **Effect reported**: positive
- **H2 concentration**: 5%

## 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)

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> **Cite as**: H2 Papers — PMID 33942780. https://h2-papers.org/en/papers/33942780
> **Source**: PubMed PMID [33942780](https://pubmed.ncbi.nlm.nih.gov/33942780/)