The disease, macular degeneration, destroys the central portion of the retina, the light-gathering cells at the back of the eye. Among people who already have significant yellowish deposits accumulating at the back of their eyes — the hallmark of the disease — the supplements cut their risk of vision loss by one-fifth.
The macular degeneration vitamin supplements — a combination of zinc and the antioxidants vitamin C, vitamin E and beta-carotene — did not appear to slow the early stages of the disease, when the yellowish deposits develop, but that is a normal part of aging and is not necessarily of concern. Almost everyone over age 70 has at least one or two of them.
As the disease progresses, the center of the field of view begins to blur, making it difficult to read, drive and recognize faces. Victims must rely on their peripheral vision, looking out of the corners of their eyes and missing much of the color and detail.
Glaucoma and cataracts strike more people than macular degeneration, but effective treatments exist for those diseases. This is the one disease for which there was nothing prior to this. At best, laser surgery can slow down the growth of abnormal blood vessels in the most severe cases of macular degeneration.
Earlier studies had indicated that people who eat large amounts of fruits and vegetables, which contain vitamins and beta-carotene, are at lower risk of developing macular degeneration. An earlier, smaller clinical study had suggested zinc might be helpful.
Among those whose disease had progressed to the intermediate stage, the zinc supplements reduced by 11 percent the risk of the disease progressing to the advanced stage, and the antioxidants reduced the risk by 10 percent. When the two were combined, the risk dropped by 19 percent. The study followed the participants for 6.5 years on average.
The daily dosages of the antioxidants used in the study were 500 milligrams of vitamin C, 400 IU of vitamin E and 15 milligrams of beta-carotene, a molecule that provides the color of carrots and sweet potatoes. The body converts the beta-carotene into vitamin A. The daily dosage of zinc was 80 milligrams with 2 milligrams of copper. High levels of zinc can cause a deficiency of copper in the body, which can lead to anemia.
Those amounts are well above the usual levels recommended by the Food and Drug Administration: three times as much vitamin A, eight times as much vitamin C, 13 times as much vitamin E and five times as much zinc.