No differences in the rate of total dementia and the rate of Alzheimer’s disease were observed between groups receiving ginkgo biloba or placebo for 6.1 years, according to results of a randomised, placebo-controlled clinical trial published in the new issue of the Journal of the American Medical Association.
“To our knowledge, the [Ginkgo Evaluation of Memory] GEM Study is the largest and first adequately powered randomized clinical trial conducted to evaluate the effect of G biloba on dementia incidence,” wrote lead author Steven DeKosky from the University of Pittsburgh.
The study challenges previous clinical trials in Germany and France that reported long-term improvements in cognitive function in older adults with dementia following gingko supplementation.
Indeed, the US trade associations have been quick to hit back at the study. Daniel Fabricant, PhD, vice president for scientific and regulatory affairs at the Natural Products Association called the study “irrelevant”.
“This study is also in direct contrast to other research,” said Fabricant. “Unfortunately, there is still no proven treatment to prevent Alzheimer’s, but reputable research has shown that Ginkgo biloba can play a constructive role in improving the symptoms related to this debilitating disease and possibly delaying its onset.”
Michael McGuffin, president of the American Herbal Products Association added: “The study does not in any way undermine what has already been observed with regard to the usefulness of ginkgo extract… in providing symptomatic relief in persons who already suffer from dementia or Alzheimer’s disease.”
Ginkgo is derived from the leaves of the ginkgo tree and has been used for thousands of years by the Chinese as a herbal remedy for a variety of ailments. It contains potent antioxidants called flavoglycosides that have been shown to have neuro-protective effects in animal models of spinal cord injury.
The GEM Study involved 3,069 community volunteers with an average age of 79.1. The majority of the participants had normal cognition (2,587), while the other 482 had mild cognitive impairment at the start of the study. The volunteers were randomised to receive either a daily placebo or a twice-daily dose of 120-mg extract of ginkgo biloba.
Over the course of 6.1 years, 246 participants in the placebo group (16.1 percent) and 277 participants in the ginkgo biloba group (17.9 percent) were diagnosed with dementia. The researchers reported no differences in the rate of total dementia or the rate of Alzheimer-type dementia between the two groups.
“One potential limitation of the trial is that, because the delay from initial rain changes to clinical dementia is known to be long, it is possible that an effect of G biloba, positive or negative, may take many more years to manifest,” wrote DeKosky and his co-workers.
“Despite this limitation, the GEM Study is by far the longest prevention trial conducted with this intervention,” they wrote.
In an accompanying editorial, Lon Schneider from the University of Southern California, Los Angeles, said the new 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”.
Commenting on the study, Dr Fabricant said the study had two major limitations: “One, it looks exclusively at people almost 80 years old who are far more likely to have Alzheimer’s, while ignoring those in middle ages, where the risk for developing the disease rises quickly and prevention could best be analyzed,” he said.
“Two, it excludes completely any consideration of the strong and established role that family history plays with Alzheimer’s. You can’t do a study on the weather without looking at wind and rain.”
Source: Journal of the American Medical AssociationVolume 300, Issue 19, Pages 2253-2262“Ginkgo biloba for Prevention of Dementia - A Randomized Controlled Trial”Authors: S.T. DeKosky, J.D. Williamson, A.L. Fitzpatrick, et al.
Editorial: Journal of the American Medical AssociationVolume 300, Issue 19, Pages 2306-2308“Ginkgo biloba Extract and Preventing Alzheimer Disease”
Authors: L.S. Schneider