11 Sep 2012

It did not pass muster in a large clinical trial in the U.S., and now a similar study in Europe concludes that ginkgo biloba extract does nothing to prevent the onset of Alzheimer’s in older adults at risk for the disease. The GuidAge placebo-controlled trial tested the standardized ginkgo extract EGb761 in volunteers who complained of subjective memory problems. Recruitment began in March 2002, and more than 2,800 participants enrolled at multiple centers in France. Writing in the September 6 Lancet Neurology, researchers led by Bruno Vellas at the University of Toulouse report that over five years, 61 people in the ginkgo group developed an AD diagnosis, as did 73 patients in the placebo group. The difference was not significant. Alzforum reported top-line data from the trial in July 2010 (see ARF related news story).

In a commentary in Lancet Neurology, Lon Schneider, University of Southern California, Los Angeles, notes that GuidAge, the U.S. Ginkgo Evaluation of Memory (GEM) trial (see ARF related news story), and numerous other trials together are evidence that “ginkgo biloba does not prevent dementia in elderly individuals with or without memory complaint or cognitive impairment, and is not effective for prevention of Alzheimer’s disease.”

This would sound final to most, but some may still hold out hope that the leaves of this Chinese tree might make a treatment eventually. In fact, GuidAge researchers call for further investigation. They note several study limitations that leave the data open to interpretation, the main one being much lower incidence of dementia in the trial than expected. This may be due to selection bias, since many of the participants had a high level of education, which protects against dementia. Whatever the reason, it left subgroup analysis on statistically shaky ground. Hints that the extract protected men, people who reported at baseline that they drank alcohol, and those who stayed on the treatment for at least four years should be interpreted cautiously, according to the authors. Schneider noted that the last effect can be attributed to incidence rising dramatically in the placebo group in the last three months of follow-up, not to any protection in the treatment group.

Hope that ginkgo improves cognition was dealt another blow in the September 5 Neurology. Researchers led by Jesus Lovera at Louisiana State University, New Orleans, report that gingko does not improve cognition in patients with multiple sclerosis. The small trial recruited 120 people. Over 12 weeks, 61 received the same dose of the extract (120 mg twice daily) used in the GuidAge trial.—Tom Fagan