A randomized clinical trial involving over 3,000 elderly people in the US found that the popular herbal supplement Ginkgo biloba fared no better than placebo at preventing dementia or Alzheimer’s disease.
The research was the work of the Ginkgo Evaluation of Memory (GEM) Study Investigators who are based at centers throughout the US, including the University of Pittsburgh, Pennsylvania, where lead author Dr Steven T DeKosky, was working at the time of the investigation. The findings are published in the 19 November issue of the Journal of the American Medical Association, JAMA.
Ginkgo biloba is taken by many people because of claims that it benefits memory and cognition and in some parts of the world it is prescribed for such. But there have been no substantial clinical trials to evaluate the effectiveness of the supplement in the primary prevention of dementia, wrote the authors.
More than 5 million people in the United States are currently affected by dementia and Alzheimer’s in particular. This chronic disease is a leading cause of age-associated disability requiring long term care, according to DeKosky and colleagues.
The randomized, placebo-controlled clinical trial included 3,069 community-dwelling volunteers aged 75 and over and took place at five US medical research centers between 2000 and 2008. About half the volunteers were given a twice daily dose of 120mg extract of Ginkgo biloba and the other half took a placebo.
None of the participants showed signs more advanced than mild cognitive impairment at the start (2,587 had normal cognition while 482 had mild cognitive impairment). They were followed for a median period of 6.1 years during which time they underwent 6-monthly assessments for dementia.
The results showed that:
- During the period of the study, 523 participants were diagnosed with dementia: 16.1 per cent (246) in the placebo group and 17.9 per cent (277) in the Ginkgo biloba group.
- 92 per cent of all the dementia cases were classed as possible or probable Alzheimer’s Disease (AD), or AD with evidence of the tell-tale signs of AD in the brain (vascular disease that shows as changes in the blood vessels).
- The overall prevalence rate of dementia did not differ significantly between the two groups: 3.3 dementia cases per 100 persons per year of exposure for the Ginkgo biloba group and 2.9 per 100 for the placebo group.
- There was a similar lack of significance for Alzheimer’s prevalence: 3.0 persons per 100 per year of exposure in the Ginkgo biloba group and 2.6 per 100 in the placebo group.
- Ginkgo biloba appeared to have no impact on the rate of progression to dementia in the participants who had mild cognitive impairment.
- There were no significant differences between the groups in the rate of side effects.
The authors concluded that:
“Based on the results of this trial, Ginkgo biloba cannot be recommended for the purpose of preventing dementia.”
They also said that these findings confirm the idea that randomized trials play a crucial part in the evaluation of new traditional pharmaceutical and complementary therapies alike and show that it is important to include older people in randomized trials of treatments that claim to be effective at preventing or delaying dementia.
In an accompanying editorial, Dr Lon S Schneider from the University of Southern California, Los Angeles, wrote that two decades of research using standardized extracts of Ginkgo biloba have yielded no definitive answer about its effectiveness. Preclinical scientific reports sing its praises but have failed to identify the active compounds and the claims have not been proved in clinical research.
“The clinical research, in turn, has not adequately defined potential cognitive indications, potentially effective dosing ranges, pharmacodynamic markers, or convincing evidence for efficacy for any one cognitive condition,” wrote Schneider.
“The GEM study adds to the substantial body of evidence that Ginkgo biloba extract as it is generally used does not prevent dementia in individuals with or without cognitive impairment and is not effective for Alzheimer disease,” he added.
“Ginkgo biloba for Prevention of Dementia: A Randomized Controlled Trial.”
Steven T. DeKosky; Jeff D. Williamson; Annette L. Fitzpatrick; Richard A. Kronmal; Diane G. Ives; Judith A. Saxton; Oscar L. Lopez; Gregory Burke; Michelle C. Carlson; Linda P. Fried; Lewis H. Kuller; John A. Robbins; Russell P. Tracy; Nancy F. Woolard; Leslie Dunn; Beth E. Snitz; Richard L. Nahin; Curt D. Furberg; for the Ginkgo Evaluation of Memory (GEM) Study Investigators.
JAMA, Vol. 300 No. 19, pp 2253-2262, November 19, 2008.
Sources: JAMA.
Written by: Catharine Paddock, PhD