Ginkgo biloba in the prevention of Alzheimer's disease or dementia

Ginkgo Biloba Shows No Benefit in Prevention of Dementia, Alzheimer's Disease CME/CE
News Author: Susan JeffreyCME Author: Désirée Lie, MD, MSEd Disclosures

November 20, 2008 — Results of a randomized trial show no beneficial effect of Ginkgo biloba in the prevention of Alzheimer's disease or dementia in subjects with normal cognition or in those with mild cognitive impairment.
The findings from the Ginkgo Evaluation of Memory (GEM) trial are published in the November 19 issue of the Journal of the American Medical Association.
The results of this trial are published hard on the heels of a negative trial with other supplements, vitamin E and vitamin C, in the prevention of cardiovascular disease and stroke in the Physicians' Health Study II. Results of that study were published in the November 12 issue of the Journal of the American Medical Association and were reported at the American Heart Association Scientific Sessions 2008. A second analysis looking at cancer was reported this week at the American Association on Cancer Research prevention conference and, similarly, showed no benefit of either agent in the prevention of cancer.
These outcomes underline the importance of randomized controlled clinical trials to assess the safety and efficacy of these agents, said GEM study coauthor Steven T. DeKosky, MD, from the University of Pittsburgh in Pittsburgh, Pennsylvania, and now is at the University of Virginia School of Medicine in Charlottesville.
"One of the major outcomes of this study is we proved you can actually do the study," he told Medscape Neurology & Neurosurgery. GEM is among the first trials that recruited a new cohort to look at a cognitive outcome using a supplement to actually finish and report findings. "It's disappointing," he says of their results, "but it's the way the science has to be done. The design would have been identical if it were a medication from a major pharmaceutical company, and not an over-the-counter alternative medication."
Preservation of Memory
In their study, the authors note that G biloba is prescribed in some areas of the world for the preservation of memory, although no medications are approved for the primary prevention of dementia. In the United States, worldwide sales of G biloba exceed $249 million annually.
The purported effect of G biloba is by the action of multiple antioxidants, although a recent in vitro study also suggested that has an antiamyloid aggregation effect, they note. Studies of G biloba in the setting of dementia have had mixed results, although a Cochrane Collaboration Review in 2007 found the evidence of a benefit, "not convincing," the study authors write.
The current study was a randomized, placebo-controlled clinical trial carried out at 5 academic medical centers in the United States to see whether treatment with G biloba in a dose of 120 mg 2 times/day could prevent incident dementia or Alzheimer's disease vs placebo. A total of 2587 subjects older than 75 years with normal cognition at baseline, and 482 subjects with mild cognitive impairment were included. Patients were assessed every 6 months for dementia.
After a median follow-up of 6.1 years, 523 subjects were diagnosed with dementia, 246 (16.1%) in the group taking placebo, and 277 (17.9%) in those taking G biloba. Of the total dementia cases, 92% were classified as possible or probable Alzheimer's disease or Alzheimer's disease with evidence of cerebrovascular disease.
The rate of total dementia did not differ between groups, with 3.3 vs 2.9 cases per 100 person-years with G biloba vs placebo. The rates of Alzheimer-type dementia were also similar, at 3.0 vs 2.6 cases per 100 person-years with G biloba vs placebo.