New research findings published this week on a standardized Ginkgo biloba extract are very limited and the public should focus on the well-documented cognitive and cardiovascular benefits of ginkgo, said the American Botanical Council (ABC), an independent nonprofit research and education organization.
A new study of previously published data being published in this week's issue of the Journal of the American Medical Association (JAMA) has reported that a leading ginkgo extract did not reduce the decline in cognitive impairment in older adults.
"There are many significant limitations of this study," said Mark Blumenthal, ABC founder and executive director.
First, the data being published this week are drawn from a previous clinical trial which was not designed to determine the decline in cognition. Second, about 40% of the subjects dropped out over the 6-year duration of the trial; the statistics reported in the study include the dropouts for which no final data are available. Further, the subjects in the study were not monitored for certain cognitive parameters until several years after the trial began, creating difficulty in determining accurately whether they experienced a decline in cognition or not. Also, the age of the subjects is quite advanced, at an average of 79 years at the beginning of the trial. This age group is not typical of the age of both healthy people and those with mild cognitive impairment who use ginkgo for improving mental performance.
Further, ABC noted that another weakness of this trial is the lack of an active control, i.e., a potential third arm of the trial (i.e., besides the patients on ginkgo or placebo) in which patients would have used a pharmaceutical medication with presumed efficacy, to determine to what extent the particular population being tested would respond. This was not possible for this trial since no conventional pharmaceutical drug has ever demonstrated the ability to prevent the onset of dementia or diminish its progression.
ABC also stated that several recent publications have demonstrated an improvement in cognitive performance in subjects using the same German gingko extract.
The new publication, by Beth E. Snits, Ph.D., a neuropsychologist associated with the University of Pittsburgh, and other colleagues, analyzed outcomes from the Ginkgo Evaluation of Memory study (GEM, published in 2008 in JAMA) to determine if ginkgo extract slowed cognitive decline in older adults who had either normal cognition or mild cognitive impairment at the beginning of the study.
The GEM study previously found that ginkgo extract was not effective in reducing the incidence of Alzheimer dementia or dementia overall. This large, randomized, double-blind, placebo-controlled, multi-centered clinical trial included 3,069 community-dwelling subjects (aged 72 to 96 years) who received either a dose of 120 mg of ginkgo extract twice daily or an identical-appearing placebo. The trial was conducted at 6 academic medical centers in the United States between 2000 and 2008, with a median follow-up of 6.1 years. Change in cognitive function was evaluated by various tests and measures.
ABC emphasized that the original GEM trial was designed to determine whether taking ginkgo would prevent the onset of dementia. What this new publication has done is attempted to analyze the possible decline in levels of cognitive function -- not a primary outcome measure of the GEM study.
"This trial is not conclusive nor should it in any way detract from ginkgo's reputation as a useful dietary supplement to help support and improve cognitive function and enhance peripheral circulation -- conditions for which it has been reported to be effective in numerous clinical trials," reminded Blumenthal.
At least 16 controlled clinical trials have evaluated various ginkgo extracts for healthy, non-cognitively impaired adults. A systematic review has shown that in 11 of these trials, the ginkgo increased short-term memory, concentration and time to process mental tasks.
"The results of this new trial must be viewed in proper perspective," noted Blumenthal. "There is a vast body of pharmacological and clinical research supporting numerous health benefits for ginkgo extracts, particularly for improving various symptoms and conditions associated with declining cognitive performance and poor circulation."
ABC also emphasized that this publication, and the one published in 2008 on which it is based, both underscore the relative safety of ginkgo extract: the amount of adverse events were basically the same in both the ginkgo and placebo groups, particularly no serious adverse effects, e.g. no statistically significant incidence of coronary heart disease, stroke of any type, and major bleeding.
The trial utilized EGb 761(R), the world's most clinically tested ginkgo extract, produced by W. Schwabe Pharmaceuticals in Karlsruhe, Germany.
American Botanical Council