Caffeine could offer some relief for those who suffer with dry eye syndrome—in particular a subset of people with genetic variations in two genes, Japanese researchers say. Apart from knowing that caffeine increases the secretion of saliva and digestive juices, the team was aware that individuals respond differently to caffeine.

The researchers analyzed DNA samples of the participants for two genetic variations that are known to play a role in metabolizing caffeine. Their study results showed that participants with genetic variations in the ADORA2A and CYP1A2 genes had greater tear production after caffeine consumption.

Arita R, Yanagi Y, Honda N, et al. Caffeine increases tear volume depending on polymorphisms within the adenosine A2a receptor gene and cytochrome P450 1A2. Ophthalmol. 2012 May;119(5):972-8.