Safety of inhaled hydrogen gas in healthy mice
Cole AR, Raza A, Ahmed H, Polizzotti BD, Padera RF, Andrews N, Kheir JN. · Medical Gas Research. 2019;9(3):133–138.
Study at a glance
Preclinical
Healthy ten-week-old female CD-1 mice exposed continuously in a gas-tight chamber.
Continuous chamber exposure to hydrogen diluted in medical air for 72 hours, with food and water available. · Source gas contained 3.2% H₂, 21% O₂ and balance N₂ and was titrated toward 2.4% chamber H₂. Mean measured exhaust concentration was 2.27% (95% CI 2.26–2.29%) and mean H₂-group total gas flow was 6.5±0.3 L/min.
Continuous 72-hour exposure.
All mice survived. Body weight, total SHIRPA score, blood tests, blood gases and major-organ histology did not differ materially. Spontaneous locomotor activity fell in the H₂ group (p<0.0001), and two exposed mice had more prominent respiratory-epithelial secretory vesicles without structural injury; the authors considered the locomotor finding potentially artifactual but did not dismiss it.
Female mice only, one concentration and duration, bloodwork in only five animals per group, many endpoints and unequal total gas flow between H₂ and control chambers. The authors calculated an 86% chance of at least one statistically significant result across the many endpoints. American Heart Association, NIH-supported core facilities and philanthropic donations funded the work; authors declared no related conflicts.
What kind of evidence is this?
Preclinical
Controlled blinded safety-screening experiment
Other molecular hydrogen research
Inhaled H₂
Information not yet classified
Some editorial classification fields are still pending. The source-reported outcomes and result are shown below; Hydrogenology does not infer a positive or negative signal from prose automatically.
Methods
Healthy ten-week-old female CD-1 mice exposed continuously in a gas-tight chamber.
50 mice: H₂ group n=25 and medical-air control n=25; blood tests and electron microscopy used smaller subsets of n=5 per group.
Continuous 72-hour exposure.
Continuous chamber exposure to hydrogen diluted in medical air for 72 hours, with food and water available.
H₂ alone diluted in medical air — not Brown's gas.
Source gas contained 3.2% H₂, 21% O₂ and balance N₂ and was titrated toward 2.4% chamber H₂. Mean measured exhaust concentration was 2.27% (95% CI 2.26–2.29%) and mean H₂-group total gas flow was 6.5±0.3 L/min.
Approximately 148 mL/min H₂, calculated from the reported mean 6,500 mL/min total flow × mean measured 2.27% chamber H₂ concentration.
Approximately 21% O₂ in the medical-air carrier; approximately 1,365 mL/min O₂ calculated from 6,500 mL/min × 21%.
Medical air at 3.0 L/min for the same 72-hour chamber exposure.
Outcomes and reported result
Survival, body weight, blinded SHIRPA neurobehavioral testing, spontaneous locomotor activity, complete blood count, serum chemistry, arterial blood gases, light microscopy of major organs and electron microscopy of airway epithelium.
All mice survived. Body weight, total SHIRPA score, blood tests, blood gases and major-organ histology did not differ materially. Spontaneous locomotor activity fell in the H₂ group (p<0.0001), and two exposed mice had more prominent respiratory-epithelial secretory vesicles without structural injury; the authors considered the locomotor finding potentially artifactual but did not dismiss it.
The complete free article, source and measured gas concentrations, total flows, full safety panel, positive and null findings, limitations, funding and conflict statement were checked.
A reported association, difference or mechanism is not automatically a clinical benefit.
Limitations and applicability
Female mice only, one concentration and duration, bloodwork in only five animals per group, many endpoints and unequal total gas flow between H₂ and control chambers. The authors calculated an 86% chance of at least one statistically significant result across the many endpoints. American Heart Association, NIH-supported core facilities and philanthropic donations funded the work; authors declared no related conflicts.
A preclinical safety screen in healthy mice; it cannot establish long-term or patient safety, higher-dose safety or therapeutic benefit.
No single-study GRADE certainty rating is assigned. Read how records and evidence assessments are prepared.
Sources and record status
PMID: 31552876 · DOI: 10.4103/2045-9912.266988
Open-access PubMed Central article.
Complete PubMed Central article and PubMed metadata; full-text extraction checked 9 August 2026.
10 August 2026
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