As with many areas of health, not all of these claims are backed by solid research. But while many eye health experts approach popularly marketed supplements, that tout better eye health, with skepticism, there is research that suggests at least some supplements may indeed benefit those at high risk of advanced eye diseases.
Much of this research has surrounded age-related macular degeneration, or AMD, a leading cause of vision loss. It's a big problem; 8 million people are at risk for experiencing AMD, and 1.75 million people have an advanced form of AMD, according to the National Eye Institute. It is expected that the number of people who have AMD will double by the year 2020.
So, when a large study called the Age-Related Eye Disease Study, or AREDS, found that people at high risk for advanced AMD lowered their risk of the disease by about 25 percent when treated with a high-dose combination of vitamin C, vitamin E, beta carotene, and zinc, eye health researchers took heed.
The 2001 clinical trial, sponsored by the National Eye Institute, also found that taking these supplements reduced the risk of vision loss caused by advanced age-related macular degeneration, or AMD, by about 19 percent.
However, there is no evidence from this study to suggest that taking nutritional supplements can prevent people who currently do not have vision problems from getting AMD in the future, said Dr. Emily Chew, deputy director of the Division of Epidemiology and Clinical Research at the National Eye Institute, and a lead researcher in the AREDS study.
According to the study, 50 milligrams daily of beta carotene, 500 milligrams daily of vitamin C, 400 international units of vitamin E, and 80 milligrams of zinc were found to be effective doses of each supplement.
In general, many eye health experts may recommend supplements only for those who already experience specific types of vision loss, said Dr. Penny Asbell, director of the Cornea Service and Refractive Surgery Center at Mount Sinai Medical Center in New York.
For example, according to Asbell, supplements may have more benefit to those who suffer from dry age-related macular degeneration, a less severe form of AMD, because of the slower progression of vision loss, rather than the more severe wet AMD.
In fact, Chew said, ophthalmologists should only recommend supplements if an eye exam shows yellow spots in the eye, called drusen, which is a common sign of AMD.
"Only if you have those yellow spots do supplements work for you," said Chew. "You really have to be at that intermediate stage."
The common nutrient in most eye health supplements are antioxidants, because oxidative stress, the damaging effects of reactive oxygen and toxins, is implicated in AMD, as it is in most age-related diseases, and in the aging process itself. Researchers suggest that perhaps antioxidants may help slow the progression of vision loss.
However, other types of antioxidants that are currently marketed as nutritional supplements for eye health are not backed by significant research, many experts said.