NEW YORK (Reuters Health) - A new study suggests that older adults who eat diets rich in citrus fruits, leafy greens and fish oil, but low in "glycemic index," may have a lower risk of age-related macular degeneration -- the leading cause of vision loss among older U.S. adults.

AMD, also known as "age-related macular degeneration" refers to gradual damage to the macula, a structure in the retina that allows for seeing fine detail. The condition affects more than 1 million Americans, usually after the age of 65.

A number of studies have suggested that individual nutrients, including the antioxidants lutein, vitamin C and vitamin E, can help protect against AMD. This latest study, published in the journal Ophthalmology, looked at the overall diet patterns of 4,000 older adults and the links to AMD risk.

Researchers found that participants who tended to eat fish rich in omega-3 fatty acids, or foods high in vitamin C, vitamin E, zinc, lutein and zeaxanthin, had a relatively lower risk of AMD. Lutein and zeaxanthin are plant pigments that act as antioxidants; the nutrients are found in broccoli, spinach and other leafy green vegetables, as well as egg yolks.

The study also found that diets containing foods with a low glycemic index, also appeared protective against AMD.

Not surprisingly, older adults who combined all three dietary patterns showed a decreased AMD risk as well.

Glycemic index (GI) refers to how rapidly a food causes blood sugar to rise. High-GI foods, like white bread and potatoes, tend to spur a quick elevation in blood sugar, while low-GI foods, such as lentils, soybeans, yogurt and many high-fiber grains, create a more gradual increase in blood sugar.

The blood-sugar surges associated with high-GI diets may eventually damage the macula, explained lead researcher Dr. Chung-Jung Chiu, an assistant professor at Tufts University School of Medicine in Boston.

That's because excess blood sugar interacts with other molecules, like fats and proteins, to form what are called glycated molecules, he told Reuters Health. This process, in turn, can put the body under more oxidative stress, which over time damages cells and may lead to various diseases, including

AMD.

Foods rich in nutrients that may ward off AMD -- including citrus fruits, leafy greens, oily fish like salmon and mackerel, and vegetable oils -- are also seen as beneficial for overall health. So it's a good idea to try to eat more of them, Chiu said.

This is especially true for older adults, the researcher noted, since the body's "self-defense systems" generally decline with age.

SOURCE: Ophthalmology, May 2009.