Hydration, Water Intake and Dry Eye

Key takeaways

• The evidence for drinking more water to help dry eye is much thinner than the advice suggests. The international dry eye nutrition report states that "increased water intake has not been directly tied to improved dry eye or ocular surface outcomes".
• Two respected US bodies disagree in public. The National Eye Institute tells people to drink 8 to 10 glasses a day for dry eye. The American Academy of Ophthalmology's dry eye advice does not mention drinking water at all.
• The largest study, in more than 51,000 people, found no protective association. If anything it pointed slightly the other way.
• Dry air is far better established as a dry eye factor than low body water. They are different mechanisms and get confused constantly.
• Caffeine is not a dry eye risk factor in population data. Alcohol is associated with higher risk in women.

Why this page is not just "yes, drink more water"

Drinking more water is the most repeated piece of dry eye advice there is. It is free, it sounds obviously right, and nobody is harmed by hearing it. So it gets passed along without anyone checking.

We went and checked. What follows is not an argument against drinking water. It is an honest account of how much is actually known, because customers deserve to know which advice is well established and which is a reasonable guess.

What the research actually found

The largest study on this question looked at more than 51,000 people in the Dutch Lifelines cohort, measuring total water intake from diet questionnaires and checking it against 24-hour urine volume. It did not find that drinking more water was associated with less dry eye. The association ran very slightly in the opposite direction.

That needs reading carefully. It is a cross-sectional study, meaning it photographs a population at one moment and cannot establish cause. A slight positive association could easily mean that people with dry eye have been told to drink more and are doing so. It is not evidence that water is bad for your eyes. What it does do is remove the easy assumption that the benefit is large and obvious, because in a study that size a large obvious benefit would have shown up.

The summary judgement from the field's own workshop is the clearest statement available. The TFOS Lifestyle report on nutrition and the ocular surface says:

"Drinking more water for dry eye has been used as an adjunct management strategy for patients and may also be recommended by some clinicians. However, based on the current limited studies, increased water intake has not been directly tied to improved dry eye or ocular surface outcomes. Future longitudinal studies should investigate whether increasing water intake is beneficial in patients with dry eye disease."

That is not a dismissal. It is a statement that the question has not been properly tested.

The mechanism people assume, and what has been measured

The reasoning behind the advice is intuitive: if your body is short of water, your tears will be saltier, and salty tears are what dry eye is partly measured by. Tear osmolarity is a real clinical measure and a real part of the disease.

What has actually been measured in humans is narrower than the reasoning suggests. The same TFOS report describes two studies linking plasma osmolality, a marker of general hydration, to tear osmolarity. One was a hospital cross-sectional study of 111 people, which found higher plasma osmolarity in the dry eye group than in controls. The other studied 14 healthy volunteers exercising in heat with fluid restricted, and found plasma and tear osmolarity strongly correlated.

Fourteen healthy people, deliberately dehydrated by exercising in heat, is a long way from an older adult drinking a glass less than usual on a Tuesday. The link has been demonstrated at the level of group averages under deliberate dehydration. Whether it holds for an individual under everyday conditions is a different question, and one study in a field setting found tear osmolarity was not associated with common hydration measures outside the laboratory.

Two US authorities, two different answers

This is the most useful thing on the page, because it explains why you have heard this advice with such confidence.

The National Eye Institute, part of the National Institutes of Health, lists under lifestyle changes for dry eye: "Drink plenty of water — try for 8 to 10 glasses every day". No source is cited for it. Notably, dehydration does not appear in the same page's own list of dry eye risk factors.

The American Academy of Ophthalmology's consumer advice on reducing dry eye symptoms covers air filters, humidifiers, wraparound sunglasses, avoiding fans and hair dryers, avoiding smoke, screen breaks, blinking, artificial tears, bedtime gels, warm compresses and lid cleaning. Drinking water is not among them.

Neither body is being careless. They are making different judgements about advice that is harmless, plausible and untested. Knowing that is more useful than being handed one of the two answers as settled fact.

The confusion worth clearing up: dry air is not the same as low body water

If there is one reframe to take from this page, it is this one.

The evidence that a dry environment worsens dry eye is strong, and it shows up consistently across humidity, wind, air conditioning, forced-air heating, altitude and pollution studies. The evidence that being short of water in your body worsens dry eye is weak.

These are different mechanisms. One is about water evaporating off the surface of your eye faster than your tear film can cope with. The other is about the total water in your body. They get merged into a single idea about "hydration", and the merger is why the advice feels so obviously correct.

The practical consequence is that a humidifier, getting out of the path of a vent, or wraparound glasses on a windy day are addressing a better documented problem than a larger water bottle is. That is exactly where the Academy's list puts its emphasis.

Caffeine, because everyone asks

The common belief is that coffee dehydrates you and therefore worsens dry eye. The research does not support that, and some of it runs the other way.

A population study of more than 85,000 people concluded that "dietary caffeine intake does not seem to be a risk factor for DED in the general population". Before adjusting for other health conditions, higher caffeine intake was actually associated with slightly lower dry eye risk, an association that weakened once comorbidities were accounted for.

An earlier crossover experiment in 78 people found significantly greater tear volume after caffeine than after placebo. Read its limits honestly: people with dry eye were specifically excluded from that study, and participants had abstained from caffeine for six days beforehand. It tells you what caffeine does to tear volume in caffeine-naive healthy people, not what it does for you.

Against that, a randomised trial found no change in Schirmer scores after oral caffeine compared with drinking water alone.

The honest position is that caffeine has not been shown to be a problem for dry eye at a population level, and there is no good reason to give up coffee on dry eye grounds alone.

Alcohol

Here the picture is clearer, and it differs by sex. A study of more than 77,000 people, adjusted for age, body mass index, smoking, education, income and 55 other health conditions, found alcohol use associated with increased risk of symptomatic dry eye in women but not in men. The authors described "a clear sex-specific effect on DED, presenting as a risk-factor only in females".

The same study found a mild apparent protective effect among male drinkers, which the authors themselves said warrants cautious interpretation given alcohol's broader health effects. We are not going to present that as a reason for anyone to drink.

So how much water should you drink?

For general health rather than for your eyes specifically, the National Academies publish total water intake figures, and the important detail is what "total" means: it includes water from food and from all beverages, not just glasses of plain water. Roughly 20 percent of most people's water intake comes from food. So the familiar eight glasses figure and the published totals are not measuring the same thing, and comparing them makes people think they are far behind when they are not.

There is also a ceiling worth mentioning, because this page is read by older adults. Drinking substantially more water is not automatically better, particularly for anyone taking diuretics or living with heart or kidney conditions. If you are thinking of significantly increasing your fluid intake and you take regular medication, that is a conversation with the doctor who prescribes it.

What we would actually suggest

Drink enough water to feel well. It is good for you for reasons that have nothing to do with your eyes, it costs nothing, and no study here gives any reason to avoid it.

Just do not expect it to be the thing that fixes your dry eye, and do not let it substitute for the measures that are better supported. If your symptoms are persistent, the productive next steps are working out what is actually driving them, which is what an eye exam is for, and addressing the environment your eyes spend their day in.

Frequently asked questions

Does drinking more water help dry eyes?

It has not been shown to. The TFOS Lifestyle nutrition report states that increased water intake has not been directly tied to improved dry eye or ocular surface outcomes, and calls for longitudinal studies to test it. The largest observational study, in more than 51,000 people, found no protective association.

Can dehydration cause dry eye?

Deliberate dehydration has been shown to raise tear osmolarity at group level in small studies, including 14 volunteers exercising in heat with fluid restricted. Whether everyday variation in how much you drink affects an individual's tear film is not established, and one field study found tear osmolarity was not associated with common hydration measures outside the laboratory.

The National Eye Institute says 8 to 10 glasses a day. Is that wrong?

It is what they publish, without a citation attached, and dehydration does not appear among the risk factors listed on the same page. The American Academy of Ophthalmology's dry eye advice does not mention drinking water at all. Two respected bodies genuinely differ here.

Does coffee make dry eye worse?

Population research concluded that dietary caffeine intake does not seem to be a risk factor for dry eye disease in the general population. An experiment in 78 caffeine-naive people without dry eye found higher tear volume after caffeine than placebo, and a randomised trial found no change in Schirmer scores.

Does alcohol make dry eye worse?

In a study of more than 77,000 people, alcohol use was associated with increased risk of symptomatic dry eye in women but not in men.

Is a humidifier better than drinking more water?

The evidence that dry air worsens dry eye is considerably stronger than the evidence about body water, and a humidifier appears on the Academy of Ophthalmology's list of remedies where drinking water does not. They address different mechanisms, and the environmental one is better documented.

Can I drink too much water?

Yes, and it matters more for some people than others. Anyone taking diuretics or managing heart or kidney conditions should raise a significant increase in fluid intake with their prescribing doctor rather than acting on general advice.

Sources

1. Markoulli M, Arcot J, et al. TFOS Lifestyle: Impact of nutrition on the ocular surface. The Ocular Surface. 2023.
2. Nguyen L, Magno MS, Utheim TP, Jansonius NM, Hammond CJ, Vehof J. The relationship between habitual water intake and dry eye disease. Acta Ophthalmologica. 2023.
3. Magno MS, Utheim TP, Morthen MK, et al. The Relationship Between Caffeine Intake and Dry Eye Disease. Cornea. 2023;42(2):186-193.
4. Magno MS, Daniel T, Morthen MK, et al. The relationship between alcohol consumption and dry eye. The Ocular Surface. 2021;21:87-95.
5. Arita R, et al. Caffeine increases tear volume depending on polymorphisms within the adenosine A2a receptor gene and cytochrome P450 1A2. Ophthalmology. 2012.
6. National Eye Institute. Dry Eye, last updated 6 August 2025.
7. American Academy of Ophthalmology. Remedies to Reduce Dry Eye Symptoms, reviewed 22 May 2024.
8. National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate.