June 10, 2021 – People who drink a lot of caffeine have a higher risk of glaucoma, but only if their genes already make them susceptible to eye disease, researchers say.
People with a parent or sibling diagnosed with glaucoma should consider limiting caffeine to the amount of two cups of coffee per day, says Louis Pasquale, MD, professor of ophthalmology at Mount Sinai Health System in New York City.
“It’s a suggestion,” he said. “It’s not something set in stone, but if you’re looking to lower your risk of disease, it’s something I’d definitely love to entertain.”
Pascale and her colleagues reported their findings in Ophthalmology.
Glaucoma damages the optic nerve, often due to increased pressure due to a buildup of fluid inside the eye. It can cause blindness.
The disease is more common in people with close family members who have it. And researchers have identified variants in several genes that are more common in people with glaucoma.
In previous studies, people who take large doses of caffeine have had temporary increases in eye pressure. The researchers therefore wondered if consuming caffeine over a long period of time could present a risk.
To help answer this question, Pasquale and his colleagues examined the files of more than 100,000 people. The files came from UK Biobank, a large investigation conducted in the UK. The records included information about the patients’ genes, how much tea or coffee they drank, their eye pressure, and whether they had glaucoma.
Looking at all the participants together, the researchers found no increased risk of caffeine glaucoma. In fact, they found that the people who consumed the most caffeine actually had slightly lower eye pressure.
But when they only looked at people whose genes were associated with glaucoma, they found that caffeine was linked to higher average eye pressure and also a higher risk of glaucoma.
This was especially true when they looked at the 25% of people who consumed more than 321 milligrams of caffeine – the equivalent of three cups of coffee – per day. When these people were also in the top 25% of the genetic risk for increased eye pressure, they were at a much higher risk for glaucoma. They were almost four times more likely to have the disease than people who did not consume caffeine and had the lowest genetic risk of 25%.
Researchers found that the combination of caffeine and genes increased the risk of glaucoma more than genes alone.
Researchers couldn’t find a statistical link to higher eye pressure or glaucoma for coffee, just for tea. But that’s probably due to a statistical problem, says study co-author Anthony Khawaja, associate professor at University College London Institute of Ophthalmology. “The answer is quite simple: the UK is a tea-drinking country! he said in an email. There probably weren’t enough people in the database who drink large amounts of coffee to analyze their risk for glaucoma.
People in both the top 25% for genetic risk and the top 25% for tea consumption (3 to 6 cups of tea per day) were almost three times more likely to have glaucoma compared to those of the lowest 25% for tea consumption and the lowest. 25% for the genetic risk.
However, this type of study cannot prove that caffeine increases the risk of glaucoma or ocular hypertension, even in people with genetic risk, Pasquale explains. He and his colleagues would like to do a follow-up study in which they give caffeine to groups of people with different genetic risks and then compare the effects on eye pressure.
Patients should not rely on modifying their caffeine intake to treat their glaucoma, says Asaf Achiron, MD, an ophthalmologist at Sackler School of Medicine in Tel Aviv, Israel, who has studied the relationship between lifestyle and eye pressure. Caffeine didn’t have a big effect for most of the people in the study, he points out.
“Glaucoma is a complex disease. In some cases, it continues to progress even when [eye pressure] is lowered by the declines so clearly that there are more problems here than pressure, ”he said in an email.
Still, the discovery might be worth mentioning to patients, he says. “I don’t discuss tea with my patients, I just measure their [eye pressure]. Maybe I should.