CHICAGO (AP) - High doses of antioxidant vitamins plus the mineral zinc can slow or even prevent vision loss in people with macular degeneration, an age-related eye ailment that affects more than 7 million Americans, a government study found.

The vitamin regimen could be the first effective treatment for people with intermediate stages of the disease, said Dr. Paul Sieving, director of the National Eye Institute, which conducted the study.

"This is an exciting discovery," Sieving said. The study involved daily doses of tablets containing vitamins C, E and beta-carotene plus zinc.

Macular degeneration is a leading cause of blindness in people 65 and older. Laser treatments are used in later stages of the disease to slow its progression.

The findings suggest that if all 6 million Americans with intermediate disease took antioxidants plus zinc, "over the next five years about a quarter of a million people who would have developed vision loss won't," said lead researcher Dr. Frederick Ferris.

"That's huge," he said. "It doesn't come free, but as a medical treatment these vitamins are relatively inexpensive."

The study involved 3,640 patients age 69 on average, with at least early stages of macular degeneration. The patients were followed for about six years.

The supplements had no effect on people in the earliest stages. But for those with intermediate disease, a daily vitamin supplement plus 80 milligrams of zinc reduced the risk of developing advanced disease by about 25 percent compared with a placebo. It also reduced the risk of vision loss by about 19 percent.

A parallel study by the same scientists found the vitamin-zinc combination had no significant effect on cataracts. Both studies are published in the October issue of the Archives of Ophthalmology.

Patients received 500 milligrams of vitamin C per day, along with 400 international units of vitamin E and 15 milligrams of beta-carotene. While those are substantially higher than the recommended daily doses, no significant side effects were found, the researchers said. High doses of zinc can cause anemia, but participants also took 2 milligrams of copper daily to counter that effect.

Smaller benefits were seen in subgroups of patients who received either antioxidants or zinc tablets alone.

The disease involves damage to the macula, the center of the retina at the back of the eye. In the "dry" form of the disease, light-sensitive cells in the macula break down, gradually impairing vision. The "wet" form, which is less common but more serious, involves formation of new blood vessels behind the retina that leak under the macula, causing rapid damage.

Existing treatments, involving lasers or laser-activated drugs, are designed for the wet form, said Dr. Lee Jampol, chairman of Northwestern University's ophthalmology department. "Up until this study, there really wasn't anything" for dry macular degeneration, Jampol said.

He called the results promising enough to recommend antioxidants plus zinc "for anybody with the intermediate stages of dry macular degeneration."

Jampol said patients in earlier stages or at risk for the disease should be discouraged from taking high-dose supplements because the study found no benefit and because the potential side effects of long-term use are uncertain.

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