Inhalation of molecular hydrogen increases breath acetone excretion during submaximal exercise: a randomized, single-blinded, placebo-controlled study
Hori A et al. · Med Gas Res. 2020;10(3):96–102.
Study at a glance
Human
Healthy young men
Participants breathed the test gas from a 200-L Douglas bag through a demand valve and mask. The exercise experiment used 1% H₂ from 10 minutes before cycling through 20 minutes of cycling at 60% peak oxygen uptake; the rest experiment used 35 minutes of inhalation. · 1% H₂, 21% O₂, 0% CO₂ and nitrogen balance.
Approximately 30 minutes of exposure in the exercise experiment and 35 minutes in the seated-rest experiment; crossover sessions
During exercise, the H₂ condition produced a larger rise in breath acetone and a small increase in oxygen uptake. Oxidative-stress and antioxidant measures did not differ. During seated rest, breath acetone and oxygen uptake did not differ.
Very small male-only physiological study, single blinding and short exposure. Breath acetone is an indirect metabolic measure, not a clinical or performance outcome. Authors reported no conflicts and no funding.
What kind of evidence is this?
Human
Randomized single-blind placebo-controlled crossover study with separate exercise and seated-rest experiments
Exercise and recovery
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 young men
Exercise experiment: 10 participants; seated-rest experiment: 6 participants
Approximately 30 minutes of exposure in the exercise experiment and 35 minutes in the seated-rest experiment; crossover sessions
Participants breathed the test gas from a 200-L Douglas bag through a demand valve and mask. The exercise experiment used 1% H₂ from 10 minutes before cycling through 20 minutes of cycling at 60% peak oxygen uptake; the rest experiment used 35 minutes of inhalation.
H₂ diluted in air — H₂ was the active added gas, not Brown’s gas.
1% H₂, 21% O₂, 0% CO₂ and nitrogen balance.
No fixed H₂ flow in mL/min was reported. Gas was inhaled on demand from a Douglas bag, so inspired flow varied with each participant’s ventilation.
21% O₂ in both the H₂ mixture and control gas; no supplemental O₂ was added.
Artificial air with 21% O₂, 0% CO₂ and nitrogen balance, without H₂
Outcomes and reported result
Breath acetone, oxygen uptake, respiratory and circulatory variables, oxidative stress and antioxidant activity
During exercise, the H₂ condition produced a larger rise in breath acetone and a small increase in oxygen uptake. Oxidative-stress and antioxidant measures did not differ. During seated rest, breath acetone and oxygen uptake did not differ.
Gas composition, delivery method, methods, principal results, funding and conflict statement checked in the open-access full text; independent appraisal remains incomplete.
A reported association, difference or mechanism is not automatically a clinical benefit.
Limitations and applicability
Very small male-only physiological study, single blinding and short exposure. Breath acetone is an indirect metabolic measure, not a clinical or performance outcome. Authors reported no conflicts and no funding.
Healthy young men performing the study’s submaximal cycling protocol; not patients or competitive-performance settings.
No single-study GRADE certainty rating is assigned. Read how records and evidence assessments are prepared.
Sources and record status
PMID: 33004705 · DOI: 10.4103/2045-9912.296038
Open-access full text is available through PMC.
Open-access PMC full text and PubMed bibliographic record.
10 August 2026
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