Long touted as an aid to memory, the herbal extract ginkgo biloba does not prevent or delay the progression of dementia or Alzheimer's disease, according to a clinical trial reported Tuesday involving more than 3,000 volunteers between ages 75 and 96.
The subjects swallowed round, reddish tablets twice a day for an average of more than six years, but at the end of the study, those who received ginkgo biloba were slightly more likely to be diagnosed with dementia and Alzheimer's than their counterparts who received dummy pills.
The results, published in the Journal of the American Medical Association, are sure to disappoint millions of people who take ginkgo hoping to boost their brains and stave off dementia and Alzheimer's, which affect more than 5.2-million Americans. Alzheimer's passed diabetes two years ago as the sixth-leading U.S. cause of death, according to the Centers for Disease Control and Prevention.
"No one is more disappointed that we didn't have any traction in slowing down the disease than the group that did the study," said Dr. Steven T. DeKosky, the neurologist who led the clinical trial.
The National Center for Complementary and Alternative Medicine, a branch of the National Institutes of Health, began researching ginkgo in 1999 as part of a broad effort to subject unregulated herbal remedies to the same type of scrutiny that is required of medicines seeking approval from the Food and Drug Administration. The latest study was funded primarily by the NIH.
Ginkgo biloba contains flavonoids, whose antioxidant properties have been shown to combat the chemical damage that accumulates in aging brain cells. One lab study also found ginkgo extract prevents the accumulation of beta-amyloid proteins, which cluster into plaques in the brains of Alzheimer's patients.
"There are a lot of purported reasons why ginkgo might work," said Richard Nahin, a neuroscientist at the National Center for Complementary and Alternative Medicine, who worked on the study.