The study led by William G. Christen, Sc.D., of Brigham and Women's Hospital and Harvard Medical School, Boston, and colleagues showed women taking these vitamins were 34 percent less likely to develop AMD and 41 percent less likely to develop visually significant AMD than those who did not take these vitamins.

The study involved 5205 women age 40 or older who were at high risk of heart disease, but did not have AMD when entering the study. They were randomly assigned vitamins or placebo for an average of 7.3 years. 2,607 women were treated with vitamins while 2,598 women received a placebo.

The vitamin treatment included 2.5 mg per day of folic acid, 50 mg per day of pyridoxine hydrochloride or vitamin B6 and 1 mg per day of cyanocobalamin or vitamin B12.

During the follow-up, 137 cases of AMD were recorded including 70 cases of visually significant AMD.   Fifty five AMD cases including 26 severe cases were found in the treatment group while 55 AMD cases including 44 severe cases were found in the placebo group.

Women taking the vitamin supplements were at a 34 percent lower risk of any AMD and at a 41 percent lower risk of visually significant AMD compared to those who did not receive the vitamins.

"The beneficial effect of treatment began to emerge at approximately two years of follow-up and persisted throughout the trial," the authors state in their report.

Age-related macular degeneration is a common cause of vision loss in elderly people. Doctors do not know how to effectively prevent the disease although some treatments are available for severe AMD.  

Previous studies have shown that vitamin B6, B12 and folic acid lower the levels of homocysteine which is associated with dysfunction of the blood vessel lining.   These vitamins are believed to be able to reverse the blood vessel dysfunction.