Aisen is director of the Alzheimer's Disease Cooperative Study (ADCS), a multi-center network spanning the United States and Canada, which conducted the clinical trial to determine if reduction of an amino acid called homocysteine would reduce the risk of Alzheimer's disease or slow its progression. Homocysteine is known to be involved in neurological disease, including Alzheimer's, and its metabolism is affected by B vitamins. Therefore, it was thought that B vitamin supplements might offer a new therapeutic approach in treating Alzheimer' disease.

"Prior studies using B vitamin supplementation to reduce homocysteine levels in patients with Alzheimer's weren't large enough, or of long enough duration to effectively assess their impact on cognitive decline," said Aisen. "This study of several hundred individuals over the course of 18 months showed no impact on cognition, although it resulted in lower levels of homocysteine in these patients."

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; to increase enrollment, 60 percent were treated with high-dose supplements and the remaining 40 percent treated with identical dosages of placebo. A total of 340 participants (202 in active treatment group and 138 in placebo group) completed the trial while taking study medication. Cognitive abilities were measured via testing with the Alzheimer Disease Assessment Scale (ADAS-cog).

The researchers found that the ADAS-cog score did not differ significantly between treatment groups, but that symptoms of depression were more common in the high-dose supplement group.

"Our study does not support the treatment of individuals with mild to moderate Alzheimer's disease and normal vitamin levels with B vitamin supplements," the authors conclude.

The ADCS, a consortium of more than 50 research institutions in the United States and Canada, is headquartered at UC-San Diego and funded by the National Institute on Aging (NIA), part of the National Institutes of Health.

Additional contributors to the paper include Lon S. Schneider, M.D., M.S.; Mary Sano, Ph.D.; Ramon Diaz-Arrastia, M.D., Ph.D.; Christopher H. van Dyck, M.D.; Myron F. Weiner, M.D.; Teodoro Bottiglieri, Ph.D.; Shelia Jin, M.D., MPH; Karen T. Stokes, B.A., B.S. and Ronald C. Thomase, Ph.D.

About Alzheimer's Disease 

Alzheimer's disease (AD) is a slowly progressive disease of the brain that is characterized by impairment of memory and eventually by disturbances in reasoning, planning, language, and perception. Alzheimer's disease is the most common cause of dementia, which afflicts 24 million people worldwide. Alzheimer's disease is not a normal part of aging and is not something that inevitably happens in later life. It is rarely seen before the age of 65. The likelihood of having Alzheimer's disease increases substantially after the age of 70 and may affect around 50% of persons over the age of 85.