The herb fares no better than placebos in preventing Alzheimer’s disease
The supplement Ginkgo biloba has failed to ward off Alzheimer’s disease or other forms of dementia any better than a placebo in a long-term trial, researchers report in the Nov. 19 Journal of the American Medical Association (JAMA).
“This is tremendously disappointing,” says study coauthor Steven DeKosky, a neurologist at the University of Virginia School of Medicine in Charlottesville.
DeKosky has good reason to feel let down. In earlier laboratory tests, ginkgo extract showed an ability to protect brain cells from the very sort of problems that occur in Alzheimer’s patients. In animal tests, the herb inhibited the clumping — or formation of plaques — of the protein amyloid-beta. These plaques are widely assumed to play a role in Alzheimer’s. Ginkgo also has antioxidant properties, further boosting its appeal.
But the new, eight-year study, the largest clinical trial ever specifically designed to test a drug or supplement for Alzheimer’s prevention, casts serious doubt on ginkgo’s usefulness. European researchers are now conducting a similar trial and are likely to present data in a year or so, DeKosky says. If those findings are also negative, he says, “That would clinch it.”
Starting in 2000, DeKosky and his colleagues randomly assigned more than 3,000 people, average age 79, to receive two ginkgopills a day or placebo pills. All participants were free of Alzheimer’s disease or other dementia at the start, but roughly one in six in each group began the study with some mild cognitive impairment. DeKosky worked on the trial while at the University of Pittsburgh.
The researchers tracked the volunteers’ progress until 2008. The participants were instructed to show up for visits at assigned clinics every six months for assessment. Each also had a partner to ensure attendance at the checkups, DeKosky says.
After an average follow-up of six years, roughly equal numbers of people taking ginkgo and people taking placebos had developed dementia, which in the vast majority of cases was Alzheimer’s disease.
The study wasn’t designed to measure cognitive gains or losses other than the dementia diagnosis, leaving open the question of whether ginkgohelped any of the volunteers’ memory in everyday activities. The supplement is also used by people hoping to promote everyday memory gains. But, says physician Lon Schneider of the University of Southern California in Los Angeles, “it is unlikely that a trial with no difference in dementia outcomes would yield significant benefit in the cognitive and functional impairment that define the dementia.” Writing in the same JAMA issue, Schneider says the new study “adds to the substantial body of evidence that G. biloba extract as it is generally used does not prevent dementia.”
Although this large trial was conducted over several years, it leaves some questions unanswered, says Barry Oken, a neurologist at the Oregon Health & Science University in Portland. The doses of ginkgoused were far smaller, pound-for-pound, than those that showed effectiveness in animal models, he says. And some of the data quality might have suffered because it is difficult to ascertain whether people were actually taking their pills, he says.
At each six-month visit, participants brought in their empty plastic pill packages. DeKosky acknowledged that there was no way to verify that the volunteers took all their pills. “But the majority of old folks are already taking medications,” he says. Participants probably put the study pills in the same weekly pill boxes they use for their regular medications and thus would be unlikely to forget to take a dose.
Other popular over-the-counter supplements such as fish oil, omega-3 fatty acids and resveratrol are being tested in large trials or are under consideration for them. Although trials that assess long-term prevention are expensive — the recent study cost $30 million — they are the only reliable way to test products against Alzheimer’s and other slow-developing diseases, says Neil Buckholtz, a neuroscientist at the National Institute on Aging in Bethesda, Md., which cofunded this study.
U.S. sales of ginkgo averaged $170 million from 2000 to 2004.
DeKosky ST et al. Ginkgo biloba for prevention of dementia. 2008. Journal of the American Medical Association, Nov. 19, Vol. 300, p. 2253-2262.
Schneider LS. Ginkgo biloba extract and preventing Alzheimer’s disease. 2008. Journal of the American Medical Association, Nov. 19, Vol. 300, p. 2306-2308.
Bower, B. Would-be brain boosters need data lift. 2002. Science News, May 25, Vol. 161, p. 333.
Dodge HH et al. A randomized placebo-controlled trial of ginkgo biloba for the prevention of cognitive decline. 2008. Neurology, May 6, Vol. 70, p. 1809-1817.