Can Coffee Treat Dry Eye Syndrome? Japanese Study Says Yes

If your eyes feel chronically dry, irritated, or even painful—especially after long screen sessions—you’re not alone. Dry eye syndrome affects millions, causing discomfort that ranges from mild grittiness to serious vision impairment. But what if something as simple as your daily coffee habit could help?

Yes, according to a controlled study by Tokyo University Medical School: patients who took caffeine pills produced significantly more tears. Out of 78 participants, those given caffeine saw measurable improvement, especially if their genetics allowed efficient caffeine metabolism.

The Tokyo University Dry Eye & Caffeine Study

Researchers at Tokyo University Medical School conducted a two-phase trial with 78 dry eye patients. In the first phase, one group received caffeine pills while the other got placebo pills. In the second phase, the groups switched treatments. No participant knew which pill they were taking. For six days prior to each phase, all avoided caffeine and other medications to control variables.

The results? Every time a patient took a caffeine pill, their tear production increased measurably. When they switched to placebo, the effect disappeared.

Why Caffeine Might Boost Tear Production

Caffeine doesn’t just wake up your brain—it stimulates your autonomic nervous system, which can trigger glands to produce more fluids. In this case, those fluids include tears, but also saliva and digestive juices. The Tokyo team found the effect wasn’t universal: individual responses depended heavily on how quickly a person metabolizes caffeine.

Genetic Factors That Change How You Process Caffeine

Not everyone reacts to caffeine the same way. Researchers identified two specific DNA variations that affect caffeine metabolism. Patients with these variants processed caffeine more efficiently—and consequently saw a stronger boost in tear production after taking caffeine pills. That means your genes play a role in whether coffee (or caffeine pills) can help your dry eyes.

Dry Eye Basics & Non-Coffee Care Tips

Dry eye syndrome can cause burning, redness, blurred vision, and eye fatigue. Common advice from experts includes staying hydrated, reducing screen time, and avoiding extended contact lens wear, since lenses can disrupt tear film and dehydrate the eye surface.

Nutrition also matters: Vitamin E (found in walnuts and peanuts) helps clear eye toxins and may prevent cataracts; Vitamin B1 (in leafy greens) supports nerve health; and green or black tea (rich in lipopolysaccharides) may improve blood production and offer mild radiation protection. Also, foods rich in Vitamin A—like the (chrysanthemum) used in traditional teas—support overall eye health, especially against dryness from overuse or screen exposure.

Frequently Asked Questions

How many dry eye patients were involved in the Tokyo University study?

The study included 78 dry eye patients. They were divided into two groups, with one group receiving caffeine pills and the other receiving placebos in the first phase, then switching during the second phase.

Did all patients see better tear production from caffeine?

No, not all patients benefited equally. Those with specific genetic variations that improved their caffeine metabolism had a stronger increase in tear production after taking caffeine pills.

What genetic factors affect how caffeine influences tear production?

Researchers found two DNA variations that alter how individuals metabolize caffeine. People with these genetic traits process caffeine more efficiently, leading to greater tear production when consuming caffeine.

Can drinking coffee have the same effect as taking caffeine pills?

The study used caffeine pills to control dosage, but it’s likely that drinking caffeinated coffee could have a similar effect—depending on your caffeine metabolism and genetics. However, exact tear-production results would vary by individual and preparation.

What are common non-caffeine tips for managing dry eye syndrome?

Experts recommend staying hydrated, reducing screen time, wearing contacts less often, and eating foods rich in Vitamins A, B1, and E. Drinks like green or black tea may also support eye health due to their antioxidant properties.

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