Taking B vitamins could lower the risk for a leading cause of blindness in older Americans, a study reports.

"This is the first randomized trial to indicate a possible benefit of folic acid, B-6 and B-12 vitamin supplements in reducing the risks of age-related macular degeneration," says study author William Christen, an associate professor of medicine at Brigham and Women's Hospital in Boston.

Christen and his colleagues collected data from a cardiovascular disease trial involving more than 5,200 women over 40 who reported they did not have macular degeneration at the study's start.

The women had been randomly assigned to take either a daily combination of folic acid, B-6, and B-12 supplements or a placebo. They answered yearly questionnaires for about seven years to track pill adherence and the development of new diseases. At study's end, 55 cases of age-related macular degeneration were confirmed in the vitamin group and 82 were confirmed in the placebo group.

Those who took the supplements had a 41% lower risk of being diagnosed with the disease. Even though the study involved only women, the researchers say, the findings probably apply to all older Americans.

"These finding are the first to suggest a possible early prevention measure," Christen says.

The study, paid for by the National Eye Institute, appears in this week's Archives of Internal Medicine.

An estimated 1.75 million people have advanced age-related macular degeneration, and 7.3 million are in early stages of the disease, he says. Few treatments exist, and they are only for advanced forms.

High blood levels of an amino acid, homocysteine, have been linked to a greater risk for age-related macular degeneration, Christen says. "It's fairly well-established that folic acid, B-6 and B-12 can reduce blood levels of homocysteine, so there's a reason to suspect a possible benefit."

More research is warranted, partly to determine the amounts of vitamins necessary to benefit eye health, Christen says. The doses taken in the study were higher than the daily recommended doses, he says.

Another drawback: "The study did not include rigorous eye examinations or retinal photos," says Sophie Bakri, associate professor of ophthalmology, vitreoretinal diseases and surgery at the Mayo Clinic. The macular degeneration diagnoses were obtained by reviewing the participants' questionnaires and medical records.

"We also need future rigorous clinical trials in other populations," Bakri says.