Dry eye is one of the few conditions where molecular hydrogen has been tested in people as well as in animals. A 2021 study from the ophthalmology department at Keio University in Tokyo gave volunteers a hydrogen-generating supplement and measured their tear film over the following hour [1]. The headline result was positive, but what was measured, in whom, and for how long matters more than the headline.
What the Study Tested
The human arm was a randomized crossover trial in 10 Japanese adult volunteers aged 29 to 41. On one day each person drank 500 mL of mineral water alone. On another day, one to three days apart and in random order, they drank the same water with 10 capsules of SUPER H2, which the authors describe as a persistent hydrogen-generating supplement [1]. Measurements were taken before the dose and at 10, 30 and 60 minutes afterward.
This was not a trial in people with diagnosed dry eye. Anyone using prescription eye drops was excluded, and the authors say only that some participants may have had mild dry eye because several reported symptoms [1]. The investigators taking the measurements were not blinded to which day was which.
What Changed in the Hour After the Dose
Exhaled hydrogen was higher 30 minutes after the capsules than after water alone (p = 0.006), which confirms the supplement delivered hydrogen [1]. Tear film breakup time, how long the tear layer stays intact between blinks, was longer at 30 minutes than after water (p = 0.00041). Tear meniscus height, a measure of how much tear fluid sits along the lower lid, was higher at 30 and 60 minutes (p = 0.042 at both).
Symptoms were rated on a simple 0 to 100 scale for three items. Eye fatigue was lower 30 minutes after the capsules than after water (p = 0.014), and dry eye sensation was lower at 30 minutes (p = 0.049), just under the usual cutoff for significance. Foreign body sensation did not differ, and no side effects were reported [1].
Those ratings are not the questionnaires clinicians use to diagnose dry eye. The 2025 TFOS DEWS III diagnostic report recommends screening with the OSDI-6 questionnaire and confirming with tests such as a non-invasive breakup time under 10 seconds [2]. The Keio trial used a dye-based breakup time and its own three-item scale, so its numbers say nothing about moving anyone into or out of a dry eye diagnosis.
The Mouse Data Behind the Human Result
The paper also ran two mouse experiments with five mice per group [1]. In healthy mice, the supplement increased tear secretion from 10 minutes after dosing, and the difference lasted up to 60 minutes. In a stress-induced dry eye model, mice were restrained in a tube under a stream of air for four hours a day over four days. Hydrogen limited the drop in tear secretion seen in untreated mice (p = 0.007) and lowered reactive oxygen species in the tear gland.
The authors are careful about what this shows. They write that most human dry eye comes from chronic disease and cannot be compared with an acute mouse model like this one [1]. They also say the fast rise in tears in healthy mice may come from a mechanism that does not involve oxidative stress, and that the mechanism still has to be worked out. So the study does not establish that hydrogen helps dry eye by acting as an antioxidant.
How to Read the Sample Size and Design
Ten people is an exploratory sample. The authors list it as a limitation, say other effects could have been missed because of it, and call for a larger study [1]. The crossover design helps, since each person is compared with themselves, but it does not replace a bigger trial.
Two other limits matter for anyone thinking about hydrogen for dry eye. Each person got one dose, and outcomes were tracked for one hour. The authors note that exhaled hydrogen was already falling after 30 minutes and that repeated dosing still needs to be studied [1]. Nothing in the paper tells you whether daily use changes the tear film over weeks or months.
The study also has a commercial tie. The senior author is the CEO of Tsubota Laboratory, a company developing dry eye products, which provided the participants’ rewards; the disclosure states that this author had a role in designing and writing the study [1]. That does not make the result wrong, but it is a reason to wait for independent replication. The trial is listed in Japan’s UMIN registry as UMIN000037169.
Where This Fits Among Dry Eye Treatments
Established dry eye care rests on a different evidence base. The 2025 TFOS DEWS III management report describes first-line care as replenishing, conserving and stimulating the tear film, with ocular supplements such as tear replacements as the cornerstone [3]. Meibomian gland dysfunction is typically treated with warm compresses and in-office eyelid treatments, and some forms of dry eye benefit from anti-inflammatory therapy.
The report also covers blinking habits, diet and changes to the environment [3]. Hydrogen is not part of that framework. The Keio trial is a reason to watch for larger, independent trials, not a reason to swap any of these treatments for a supplement.
Dry eye has several distinct drivers, from low tear volume to eyelid gland problems, and the right treatment depends on which ones you have [2][3]. If symptoms affect your daily life, an eye care provider’s diagnosis matters more than any single supplement.
Practical Takeaway
In a small, unblinded crossover trial, one dose of a hydrogen-generating supplement lengthened tear film breakup time and modestly reduced eye fatigue and dry eye sensation over the following hour in 10 adult volunteers who were not selected for diagnosed dry eye [1]. Mouse experiments in the same paper showed more tear secretion, and less tear loss under stress.
That is an early signal, not evidence of a treatment. Nobody has yet shown what happens with daily use, in people with confirmed dry eye, in a larger trial without a commercial sponsor. If dry eye is a real problem for you, it is worth mentioning to your eye doctor, alongside proven treatments rather than instead of them.
References
- Randomized, crossover clinical efficacy trial in humans and mice on tear secretion promotion and lacrimal gland protection by molecular hydrogen. Scientific Reports, 2021
- TFOS DEWS III: Diagnostic Methodology. American Journal of Ophthalmology, 2025
- TFOS DEWS III: Management and Therapy. American Journal of Ophthalmology, 2025
These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure, or prevent any disease. Content is for informational purposes only and is not medical advice; consult a qualified healthcare provider before starting any supplement. As an Amazon Associate we earn from qualifying purchases.
