Consumption of coffee can boost the eye's ability to produce tears, say researchers.
For many, dry eye syndrome is simply uncomfortable and annoying, but for others it escalates into a vision-threatening disease.
Researchers at the University of Tokyo's School of Medicine found that all of the 78 participants in the new study produced significantly more tears after consuming caffeine than after taking a placebo.
Dry eye syndrome involves malfunction of the rate of tear production, the quality of tears, and/or the rate of evaporate from the surface of the eye.
Anyone can experience dry eye, though it is more common among women. Symptoms can include gritty, scratchy or burning sensations, excessive tearing, and/or production of stringy mucus.
The research team, by Reiko Arita, MD, PhD, was motivated by an earlier study that had shown a reduced risk for dry eye in caffeine users: 13 percent of users had the syndrome compared with nearly 17 percent of non-users.
The team knew that caffeine was likely to stimulate tear glands, since it is known to increase other secretions, such as saliva and digestive juices. They also knew that people respond differently to caffeine, so they analysed study participants' DNA samples for two genetic variations that play important roles in caffeine metabolism.
Tear production proved to be higher in study subjects who had the two genetic variations.
"If confirmed by other studies, our findings on caffeine should be useful in treating dry eye syndrome. At this point, though, we would advise using it selectively for patients who are most sensitive to caffeine's stimulating effects," said Dr. Arita.
The study has been published in Ophthalmology, the journal of the American Academy of Ophthalmology.