A clinical trial led by Dr. Paul S. Aisen of the University of California, San Diego School of Medicine, said homocysteine is known to be involved in neurological disease, including Alzheimer's, and its metabolism is affected by B vitamins. It was thought that B vitamin supplements might offer a new therapeutic approach in treating Alzheimer's disease.

The study included supplementation with folic acid and vitamins B6 and B12 for 18 months in 409 individuals with mild to moderate Alzheimer's disease. Participants were randomly assigned to two groups of unequal size -- 60 percent were treated with high-dose supplements and the remaining 40 percent treated with identical dosages of placebo. A total of 340 participants completed the trial.

The study, published in the Journal of the American Medical Association, found that the Alzheimer Disease Assessment Scale score did not differ significantly between treatment groups, but that symptoms of depression were more common in the high-dose supplement group.