Although vitamin manufacturers have touted the benefits of the antioxidants lutein and zeaxanthin in promoting eye health for years, researchers say until now there has been little to support those claims.
But their study provides new evidence that these antioxidants, which are found in plants such as spinach, kale, and collard greens, can indeed help prevent cataracts by protecting the eyes from the damaging effects of ultraviolet sunlight.
"Our results are the first to provide physical evidence suggesting that lutein and zeaxanthin decrease damage caused by ultraviolet radiation," says researcher Joshua Bomser, assistant professor of nutrition at Ohio State University, in a news release.
Along with other environmental, lifestyle, and inherited risk factors associated with cataracts, researchers say exposure to ultraviolet radiation from sunlight and the stress it causes appears to be a major contributor to the development of cataracts.
Nearly 20 million people in the U.S. suffer from cataracts. The condition occurs when the lens of the eye becomes cloudy, making it difficult or nearly impossible to see clearly. The risk of cataracts increases with age.
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In the study, published in the December issue of the Journal of Nutrition, researchers examined the effects of lutein and zeaxanthin on samples of human eye lens cells in the laboratory. They also compared the effects of these antioxidants on the cells to the effects of another antioxidant thought to improve eye health, vitamin E.
Researchers treated the cells with various concentrations of the antioxidants and then exposed them to ultraviolet radiation.
"The dose of UVB radiation we used on the cells is about the same amount a person receives when they get a mild tan," says Bomser.
Adding lutein and zeaxanthin to the cells reduced signs of ultraviolet damage by 50%-60%. Vitamin E reduced the same signs of damage by 25%-32%.
"The lens is equipped with antioxidant defense mechanisms [that] guard against the harmful effects of ultraviolet radiation and oxidative stress," says Bomser. "In addition to protective enzymes and compounds like vitamins C and E, we think that low concentrations of lutein and zeaxanthin in the eye lens help shield the eye from the harmful effects of UVB radiation.
"Lutein and zeaxanthin accumulate in the retina and in the lens of the eye, but we're not sure how they reach the eye in the first place," says Bomser. "They travel through the bloodstream, but the lens doesn't have a blood supply."