Add curing dry eyes to the list of amazing things coffee can do.
In recent years, studies have shown that drinking coffee decreases people's likelihood of developing cancer, diabetes, gallstones and Parkinson's disease.
And now it's being touted as a potential treatment for dry-eye syndrome, a problem that's painful and irritating for most sufferers and can cause vision impairment in some extreme cases.
Researchers at the University of Tokyo's School of Medicine studied 78 people with dry-eye syndrome. In one session, they gave half of them caffeine pills, and the other half placebos. In the next session, they reversed the doses.
Nobody knew which pill they were getting, and all of them abstained from caffeine and other drugs for the six days leading up to the experiment.
In both sessions, those who got the caffeine pills produced more tears than those who did not.
But it's not just the java that did the trick. It also depends on people's ability to metabolize caffeine, the researchers said.
They found the participants whose DNA showed the two genetic variations that play important roles in caffeine metabolism had greater tear production after taking the caffeine pills.
The study posits that caffeine stimulates tear glands in the same way it increase other secretions, like saliva and digestive juices.
"If confirmed by other studies, our findings on caffeine should be useful in treating dry-eye syndrome," Dr. Reiko Arita said in a press release. "At this point, though, we would advise using it selectively for patients who are most sensitive to caffeine's stimulating effects."
The study has been published in the journal Ophthalmology.