A crossover trial measured what happens to eye pressure when healthy adults drink 1,260 millilitres of hydrogen-rich water in 15 minutes. Pressure went up by an average of 2.7 millimetres of mercury[1].
Before that number gets used to argue that hydrogen water is bad for your eyes, here is the rest of it. The same people, on a different day, drank the same volume of hydrogen-free water and their eye pressure went up too. The difference between the two conditions was not statistically significant[1].
The pressure rise is mostly about drinking 1.26 litres of anything in a quarter of an hour. But the study did find one thing that separated the two, and it is the part that matters if you have glaucoma.
What the study did
Twenty-four healthy volunteers, 5 men and 19 women, aged between 20 and 33, took part. One eye of each subject was measured. The design was prospective, randomized, double-blind and crossover, so each person completed both conditions on separate days in random order[1].
In each part, 1,260 millilitres of hydrogen-rich water or hydrogen-free placebo was administered over 15 minutes in three doses. Intraocular pressure and central corneal thickness were measured before intake and over the following 75 minutes[1].
Central corneal thickness was included for a good reason. Corneal thickness affects how accurately pressure readings come out, so a change in the cornea could produce an apparent pressure change that is not real. It did not change significantly during the experiment[1], which means the pressure readings reflect actual pressure.
What it found
Both drinks caused a significant increase in intraocular pressure relative to baseline. The maximum increase was 2.7 millimetres of mercury plus or minus 2.0 at minute 25 after hydrogen-rich water, and 1.4 millimetres of mercury plus or minus 2.0 at minute 35 after placebo[1].
The values did not differ significantly between the two conditions. But there were significantly more clinically significant individual pressure increases after hydrogen-rich water, in 58 percent of subjects, than after placebo, in 25 percent[1].
Those two sentences have to be read together, because they say different things. On average, the two drinks were not distinguishable. Counting how many individual people crossed a clinically meaningful threshold, they were.
With 24 people, that pattern is what you would expect either from a real but modest effect that the average washes out, or from chance in a small sample. The study cannot tell you which. The authors’ conclusion is appropriately hedged: the results indicate that acute intake of hydrogen-rich water may pose a higher risk than placebo in terms of intraocular pressure[1].
Why plain water raises eye pressure too
This is well established, and it has a name. The water drinking test is a clinical provocative test used in glaucoma care, in which a patient drinks a large volume of water quickly and their eye pressure is measured repeatedly afterwards to reveal pressure peaks that a single office reading would miss[2].
It is a real diagnostic procedure, not a curiosity. One study of it followed 99 patients treated for primary open-angle glaucoma across two sessions, examining how reproducibly the pressure peaks occurred[2]. The test exists precisely because drinking a lot of fluid quickly reliably pushes eye pressure up.
So the headline finding of the hydrogen study is, in one sense, the expected result. The volume did what volume does. The genuine question the study raises is whether the hydrogen added anything on top, and the honest answer is that the average said no and the individual-response count said maybe.
Where the hydrogen might come in
There is no established mechanism by which molecular hydrogen would raise eye pressure. Hydrogen’s documented action is reacting selectively with hydroxyl radical while leaving useful signalling radicals alone[3], and the research interest in it has been overwhelmingly as a protective agent[4].
Hydrogen-rich water also differs from plain water in ways beyond the dissolved gas, depending on how it is made. Water produced by dissolving magnesium tablets carries magnesium and a raised pH; water from an electrolysis device has its own profile. This study does not identify which component, if any, was responsible, and with a non-significant between-group difference there may be no component to identify.
The reasonable position is that this is a single small study reporting a signal that did not reach significance on its primary comparison, with no mechanism behind it, and it should be treated as a question rather than a finding.
Who was not studied
Twenty-four healthy people aged 20 to 33, mostly women. Nobody in that group has glaucoma, ocular hypertension, or the aged drainage structures that make eye pressure clinically consequential.
That is the mismatch at the centre of this page. Intraocular pressure matters because sustained elevation damages the optic nerve and causes glaucoma, and glaucoma is a disease of older adults. The people for whom a 2.7 millimetre rise could plausibly matter were not in this study.
The authors say so directly, writing that in risk groups such as subjects with glaucoma, ocular hypertension or suspected glaucoma, it is necessary to verify this conclusion by further studies[1]. That work has not been published.
What to actually do with this
If you have healthy eyes and no glaucoma risk, this study does not give you a reason to change anything. A transient pressure rise of a couple of millimetres of mercury after drinking a large volume of fluid is a normal physiological response in a healthy eye, and it settles.
If you have glaucoma, ocular hypertension, or have been told you are a glaucoma suspect, there is a genuinely useful and cost-free precaution here, and it applies to all fluids rather than to hydrogen water specifically: do not drink large volumes quickly. Spread your intake through the day. That advice long predates hydrogen water and comes straight from the fact that the water drinking test works at all[2].
The specific pattern to avoid is the one the study modelled: over a litre in under 15 minutes. Someone drinking hydrogen water from a tablet often drinks a full bottle fast, because tablet instructions typically say to drink promptly once the tablet has dissolved, so hydrogen levels are highest. That instruction is about hydrogen concentration and it happens to encourage exactly the drinking pattern that raises pressure most.
If you use hydrogen water and have any glaucoma diagnosis or suspicion, mention it to your ophthalmologist. It is a small thing to raise, and they can measure your response directly rather than relying on a 24-person study of healthy twenty-somethings.
The bottom line
In a randomized, double-blind crossover study of 24 healthy young adults, drinking 1,260 millilitres of hydrogen-rich water over 15 minutes raised intraocular pressure by up to 2.7 millimetres of mercury, and drinking the same volume of hydrogen-free water raised it by up to 1.4. The difference between conditions was not statistically significant, though significantly more individuals crossed a clinically significant threshold on hydrogen-rich water, at 58 percent versus 25 percent[1].
The dominant factor is the volume and the speed, not the hydrogen. That is a known effect used deliberately as a clinical test in glaucoma[2].
Whether hydrogen adds anything on top is unresolved, was not shown on the primary comparison, and has not been studied in the people it would matter to. The practical takeaway is about pacing your fluid intake rather than avoiding hydrogen water.
References
- Effect of acute hydrogen-rich water intake on intraocular pressure in healthy subjects. Ceska a Slovenska Oftalmologie, 2023
- Reproducibility of the Time of Intraocular Pressure Peaks During Water-drinking Test in Patients Treated for Open-angle Glaucoma. Journal of Ophthalmic and Vision Research, 2024
- Hydrogen acts as a therapeutic antioxidant by selectively reducing cytotoxic oxygen radicals. Nature Medicine, 2007
- Molecular hydrogen as an emerging therapeutic medical gas for neurodegenerative and other diseases. Oxidative Medicine and Cellular Longevity, 2012
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.
