Homocysteine is known to be involved in neurological disease, including Alzheimer's, and B vitamins affected its metabolism. 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 Dr Paul S. Aisen, professor of neurosciences at the University of California, San Diego School of Medicine.
"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," he added.
During the study, the 409 participants with mild or moderate Alzheimer's received folic acid and vitamins B6 and B12 for 18 months.
They were randomly assigned to two groups of unequal size; to increase enrolment, 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.
The 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," said the authors.
The study is published in Journal of the American Medical Association (JAMA).