By Eleanor McDermid, Senior medwireNews Reporter
The GuidAge trial of ginkgo biloba extract in people with evidence of memory problems confirms that the treatment does not reduce their risk for progression to Alzheimer's disease.
The findings, which appear in The Lancet Neurology, add to previous evidence against a protective effect of ginkgo biloba against Alzheimer's disease.
"If ginkgo biloba were a drug, and not marketed as a food supplement, clinical testing for efficacy against Alzheimer's disease and cognitive impairment would have ended long ago," writes Lon Schneider (Keck School of Medicine of the University of Southern California, Los Angeles, USA) in an accompanying commentary.
"Nevertheless, the fact that ginkgo biloba extract is widely promoted, derived from a plant, and fairly safe were reasons enough for its use in two landmark prevention trials for Alzheimer's disease."
The trial involved people aged at least 70 years who had reported memory problems to their doctors. During a median 5 years of treatment, 61 of 1406 participants randomly assigned to take standardized gingko biloba extract 120 mg were diagnosed with probable Alzheimer's disease (1.2 cases per 100 person-years).
Also, 73 of 1414 participants in the placebo group were diagnosed with probable Alzheimer's disease (1.4 cases per 100 person-years). The slight difference between the two groups equated to a nonsignificant hazard ratio of 0.84, and was largely caused by a spike in Alzheimer's disease cases in the placebo group near the end of follow up.
Several significant interactions emerged in preplanned subgroup analyses; for example, men appeared to derive a treatment benefit where women did not. But Bruno Vellas (University of Toulouse III, France) and colleagues say that these results should be interpreted with extreme caution, given the overall lack of effect of gingko biloba.
Gingko biloba treatment did not have any notable adverse effects, however. Rates of ischemic or hemorrhagic stroke, other hemorrhagic events, and cardiac events were similar in both groups.
Schneider notes that the study highlights the difficulties inherent in Alzheimer's disease prevention trials. "In particular, despite the investigators' aim to enhance the likelihood that the study sample would progress to dementia by including participants who had memory complaints, the actual incidence of dementia was less than half the expected value."
He says: "GuidAge raises a number of issues about the design and conduct of prevention trials and the need to re-examine assumptions about enrichment of study samples, including what interventions should be studied, lengths of follow-up times, and types of outcomes assessed."
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