Ginkgo biloba does not prevent onset of dementia in general or of Alzheimer's disease in particular, according to data from a large, randomized clinical trial.
Basic and observational research has suggested the herbal product should be a promising therapy, but “no adequately designed and powered clinical trial has evaluated the [herb's] safety and effectiveness in the primary prevention of dementia,” said Dr. Steven T. DeKosky of the University of Pittsburgh and his associates in the Ginkgo Evaluation of Memory study.
The National Center for Complementary and Alternative Medicine and the National Institute on Aging, Bethesda, Md., sponsored the study of 3,069 community-dwelling subjects aged 75 and older. They were randomly assigned to receive G. biloba or placebo twice daily and followed for a median of 6 years to track development of dementia (JAMA 2008;300:2253–62).
The G. biloba was a standard formulation used in many of the branded products sold in the United States and was administered at the highest, most commonly used dosage. An expert panel assessed the subjects' cognitive status, focusing on therapy adherence and subject retention, given their advanced age and concomitant morbidity.
A total of 523 subjects developed dementia, including 16% in the placebo group and 18% in the active treatment group, a nonsignificant difference. The rate of total dementia was not significantly different between subjects receiving ginkgo (3.3 cases per 100 person-years) and those receiving placebo (2.9 cases per 100 person-years), neither was the rate of Alzheimer's disease at 3 cases per 100 person-years and 2.6 cases per 100 person-years, respectively.
The findings remained consistent across subgroups of patients categorized by age, sex, and the presence or absence of mild cognitive impairment at baseline. Mortality and the adverse event profiles were similar between the groups, with similar incidence of coronary heart disease events, stroke, and bleeding events.
Because the delay from initial brain changes to clinical dementia is known to be long, it may take many years to manifest an effect of G. biloba, positive or negative, the authors wrote, and they are planning further analysis of brain function and pathology by group using MRIs.
Dr. DeKosky reported receiving grants or research support from Elan Corp., Myriad Genetics Inc., Neurochem Inc., and GlaxoSmithKline, and serving on the advisory boards of or consulting for several additional pharmaceutical companies.