Randomized, crossover clinical efficacy trial in humans and mice on tear secretion promotion and lacrimal gland protection by molecular hydrogen
Kubota M et al. · Sci Rep. 2021;11:6434.
What kind of evidence is this?
Human
Randomized two-period crossover exploratory human study with separate mouse experiments
Eye health
H₂-rich water
Not reported in this record.
Not reported in this record.
Methods at a glance
Healthy adults, some reporting dry-eye symptoms
10 human participants
Acute measurements through 60 minutes after ingestion
Ten persistent H₂-generating capsules consumed with 500 mL mineral water
Oral H₂-generating supplement — H₂ was generated after ingestion; not H₂-rich water and not Brown’s gas.
The capsule-level H₂ dose was not quantified in the article.
Not applicable — oral capsules, not gas inhalation.
No O₂ was co-delivered as part of the intervention.
500 mL mineral water without the H₂-generating capsules; 1–3 day crossover interval
Outcomes and reported result
Exhaled H₂, tear stability, tear secretion and subjective ocular symptoms
Exhaled H₂, tear stability and some dry-eye symptom measures improved after capsules. No side effects were reported; the human group was exploratory and very small.
Human intervention, methods, main results, funding and competing interests checked in the open-access full text; 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
Only 10 healthy participants, acute crossover timing, multiple ocular measures and a separate mouse model. One sponsor-author was CEO of a dry-eye product company, helped design and write the study, and the company paid participant rewards.
Healthy adults under the acute capsule protocol; not proof of treatment for diagnosed dry-eye disease.
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: 33742060 · DOI: 10.1038/s41598-021-85895-y
Open-access full text is available through PMC and the publisher.
Open-access PMC and publisher full texts plus PubMed bibliographic record.
2026-08-10