Nov. 18, 2008 -- Millions of older people take the herbal supplement ginkgo biloba in hopes that it will prevent or slow the progression of Alzheimer's disease and other age-related dementias, but one of the largest and longest studies to address the issue shows no benefit.
In the Nov. 19 issue of The Journal of the American Medical Association, researchers report that the herbal supplement showed no evidence of reducing the overall incidence of either Alzheimer's disease or dementia.
"It was worth finding out if giving this relatively benign drug to older people would have an effect," study researcher Steven T. DeKosky, MD, tells WebMD. "But based on this research, ginkgo biloba cannot be recommended for preventing dementia."
DeKosky was with the University of Pittsburgh at the time of the study. He is now vice president and dean of the University of Virginia School of Medicine.
Ginkgo vs. Placebo
It is not clear how many people in the United States take ginkgo biloba, but sales of the supplement exceeded $249 million in 2006.
Earlier studies in older people with Alzheimer's disease or other age-related dementias have generally been disappointing.
A 2007 review of 35 such trials involving about 4,200 patients found "inconsistent and unconvincing" evidence of clinically significant benefits for the supplement in people with dementia.
None of the participants in the newly reported Ginkgo Evaluation of Memory (GEM) study had Alzheimer's at enrollment, although about 500 showed evidence of mild cognitive impairment.
In all, 3,069 people aged 75 or older took part in the trial. About half the volunteers took 120 milligrams of ginkgo biloba twice a day and the other half took a placebo. Neither the patients nor the researchers knew which treatment was being given.
Over an average of six years of follow-up, 523 study participants received a diagnosis of dementia, 246 (16%) in the placebo group and 277 (18%) in the ginkgo group.
The rate of Alzheimer's disease did not differ significantly between the two groups, with 3.3 cases occurring for every 100 people treated with ginkgo biloba each year, compared to 2.9 cases in the placebo group. The researchers also found no effect on the progression of mild cognitive impairment to dementia.
Is Ginkgo Harmless?
The findings strongly argue against the use of ginkgo biloba for the prevention of mental decline in older populations, University of Southern California psychiatry and neurology professor Lon S. Schneider, MD, tells WebMD.
He notes that the GEM study is far larger and longer than any previous placebo-controlled ginkgo biloba trial.
"The message to take from this is that this intervention doesn't work," he says.
In an editorial accompanying the study, Schneider pointed to earlier trials suggesting a slight increase in strokes and mini-strokes in patients taking ginkgo biloba.
In the GEM study, there was no difference in heart attack or ischemic strokes between the ginkgo and placebo-treated patients. Ischemic strokes, the most common type of stroke, are caused by a blockage in an artery that supplies blood to the brain. There were more hemorrhagic (bleeding) strokes in the ginkgo group, but the overall number of cases was small and the difference was not found to be significant.
"The potential adverse effects of ginkgo biloba extract illustrate why it is untenable to recommend a drug or nutraceutical in the absence of efficacy evidence simply because it could possibly help and initially appears harmless," Schneider writes.
Although he acknowledges that the GEM study was well designed, Mark Blumenthal, who is founder and executive director of the American Botanical Council, tells WebMD that the trial does not represent the last word on ginkgo biloba and dementia.
"There are other trials that will be coming out," he says. "Whether or not they will show a positive result or not remains to be seen."
He cited several studies suggesting a role for ginkgo biloba in slowing the progression of dementia in elderly people already experiencing cognitive decline.
"In reporting the news that ginkgo biloba didn't work for prevention in this study, it is important not to mislead people into thinking that there is no evidence to support treatment," he says.