Long touted as an elixir of eternal mental acuity, the herbal extract ginkgo biloba in fact does not prevent or delay the progression of dementia or Alzheimer's disease, according to a clinical trial reported today involving thousands of volunteers between the ages of 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 got 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 Assn., are sure to disappoint the millions of people who take ginkgo in the hopes of boosting their brainpower and staving off the ravages of dementia and Alzheimer's, which affect more than 5.2 million Americans. Alzheimer's passed diabetes two years ago as the sixth-leading cause of death in the U.S., 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.
Mark Blumenthal, executive director of the American Botanical Council, a nonprofit group backed by herbal supplement makers, said the study used the right dose of the right ginkgo extract and gave the pills a reasonable amount of time to show an effect. The fact that it did not help puts ginkgo in good company, he said.
"Let's keep in mind that to date, no conventional pharmaceutical drug has shown any benefit for either preventing the onset of Alzheimer's or dementia, or even slowing it down," he said.
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 ginkgo tree is native to China, and its extract was used in ancient times to promote general wellness, said Dr. Wallace Sampson, editor of the Scientific Review of Alternative Medicine. About 30 years ago, Europeans began testing its effects on the mental decline that often comes with aging.
Ginkgo is prescribed by physicians to preserve memory in some European countries, including Germany. In the U.S., supplement makers tout ginkgo biloba's ability to "improve mental sharpness, concentration, memory and cognitive ability," according to one purveyor.
Companies also say it promotes blood circulation to the arms, legs and brain, thereby boosting overall physical activity levels. Americans spent $107 million on ginkgo biloba products last year, according to Nutrition Business Journal.
"People tell me, 'I took ginkgo, and I could focus for three hours -- I never got up to get coffee,' " Blumenthal said. "I get too wired on it myself."
Ginkgo biloba contains flavonoids, whose antioxidant properties have been shown to combat the chemical damage that accumulates in aging brain cells. One laboratory study also found that ginkgo extract prevents the accumulation of beta-amyloid proteins which cluster into plaque in the brains of Alzheimer's patients.
"There are a lot of purported reasons why ginkgo might work," said Richard L. Nahin, a neuroscientist at the National Center for Complementary and Alternative Medicine, who worked on the study.
Small scientific studies of the herb have produced mixed results. Ginkgo appeared to help patients with dementia and Alzheimer's in some clinical trials, but others found it had no effect.
The latest study, funded primarily by the NIH, focused on elderly men and women who had normal mental function or only mild cognitive impairment. They were recruited from voter registration rolls and private mailing lists in four areas served by large academic hospitals: Sacramento; Pittsburgh; Hagerstown, Md.; and Winston-Salem and Greensboro, N.C.
Of the 3,069 people who enrolled in the study, 1,545 took 240 milligrams a day of the ginkgo extract EGb 761, the variety used in Ginkgold products sold by Nature's Way. The other 1,524 participants took identical-looking placebos. All the pills were supplied by Schwabe Pharmaceuticals, a large supplement maker in Germany.
By the end of the study, 277 people who took ginkgo, or 18%, were diagnosed with dementia, compared with 246, or 16%, in the placebo group, according to the study. The ginkgo group also included 257 cases of Alzheimer's, versus 220 in the placebo group. None of those differences was statistically significant, the researchers said.
There was also no difference in the rate of strokes, heart attacks and other cardiovascular events between the two treatment groups.