Allen Taylor, director of the Laboratory for Nutrition and Vision Research at Tufts University in Boston, said the study was strong because patients were assigned at random and followed for a long time. But because the findings were teased out of a larger experiment for heart disease, there wasn't strict categorization of the type and severity of the eye disease, said Taylor, who does similar research but was not involved in the new study.

Among women taking the B vitamins there were 55 cases of AMD. In the placebo group, there were 82 cases. More serious cases, causing significant vision loss, totaled 26 in women taking B vitamins and 44 in those taking dummy pills.

There were too few cases of the most advanced AMD to make claims about vitamins' potential benefits, Christen said.

B vitamins lower homocysteine, a blood substance once thought to raise heart disease risk, but the nutrients weren't helpful for that in the larger study on cardiovascular disease.

The eye's small blood vessels may respond better to B vitamins' effect on homocysteine than the body's large vessels, Christen said.

It's too soon to recommend B vitamins to people who want to prevent age-related vision loss, he said. But people who already have the disease should talk to their doctors about over-the-counter eye-protecting supplements, including vitamins C and E and zinc, which prior studies have shown slow the disease.

Christen and others recommended food sources of B vitamins and folic acid such as meat, poultry, fortified cereals, beans, nuts, leafy vegetables, spinach and peas.

The study was funded by the National Institutes of Health. Vitamins and placebos were provided by chemical maker BASF Corp., which did not participate in the study otherwise. Some of the researchers reported past funding from pharmaceutical and nutritional supplement makers.

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Editor:Yang Jie