Sixty-minute inhalation of molecular hydrogen decreases blood oxygen saturation but does not alter autonomic cardiac regulation at rest in healthy females
Grepl P et al. · Can J Physiol Pharmacol. 2026;104:1–9.
What kind of evidence is this?
Human
Randomized double-blind placebo-controlled crossover study
Cardiovascular and circulatory health
Inhaled H₂
Not reported in this record.
Not reported in this record.
Methods at a glance
Physically active healthy young women
20 participants; mean age 22.1 years
Single 60-minute session per condition with a 7-day crossover washout
99.8%-pure H₂ source gas through a nasal cannula at 300 mL/min for 60 minutes while seated at rest
H₂ alone at high source-gas purity — not Brown’s gas.
99.8% H₂ source-gas purity.
299.4 mL/min H₂, calculated as 300 mL/min source-gas flow × 99.8% H₂.
No supplemental O₂ was co-delivered. The exact trace O₂ fraction was not restated in the accessible article passages reviewed for this record.
Ambient air through a modified generator at 300 mL/min
Outcomes and reported result
Continuous oxygen saturation and time- and frequency-domain heart-rate-variability indices
Mean SpO₂ was 95.9% with H₂ versus 96.7% with placebo; authors judged the difference not clinically significant. Heart-rate-variability indices did not differ (all p≥0.32).
Methods and results checked in the free article text and open Dryad dataset record; independent appraisal remains incomplete.
A reported association, difference or mechanism is not automatically a clinical benefit. Null findings, outcome type, study design and precision all matter.
Cautions and applicability
Small acute study in healthy young women. The slight SpO₂ reduction was not considered clinically significant and autonomic cardiac regulation was unchanged. Michal Botek disclosed external consultancy to H2 Global Group.
Healthy physically active young women resting under the reported laboratory protocol.
Not reported in this record.
Not reported in this record.
Not reported in this record.
No single-study GRADE certainty rating is assigned. Certainty is assessed by important outcome across a complete eligible evidence set, not by attaching a final grade to one source.
Sources and record status
PMID: 41401441 · DOI: 10.1139/cjpp-2025-0228
The publisher marks the article as free; an open study-data record is also available.
Free publisher article, PubMed record and open Dryad study-data record.
2026-08-10