Vellas B, Coley N, Ousset P-J, et al. Long-term use of standardised ginkgo biloba extract for the prevention of Alzheimer's disease (GuidAge): a randomised placebo-controlled trial. Lancet Neurol. 2012 Oct;11(10):851-9.
This study was conducted to determine the effectiveness of Gingko biloba in decreasing the incidence of Alzheimer’s disease in elderly adults with memory complaints. It involved 2,854 participants (age 70 and older) who were randomized to receive 120 mg of a standardized gingko extract, twice a day, or a placebo. At the 5-year follow-up point, all subjects received at least one dose of the ginkgo extract or the placebo. Sixty-one participants in the ginkgo group and 73 in the placebo group were diagnosed with probable Alzheimer’s disease (95% CI 0·60–1·18; p=0·306). There was no difference in the incidence of adverse effects between the two groups.Researchers concluded that long-term supplementation with a ginkgo extract did not prevent the onset of Alzheimer’s disease in the elderly.
However, data analysis shows that at >5 years, the protective effects of ginkgo extract are greater than the placebo.
Also, the study has limitations: A high dropout rate at the beginning of the trial, and a selection bias toward individuals with higher levels of education.
Further studies are needed to clarify the role of ginkgo in preventing memory loss.
DeKosky ST, Williamson JD, Fitzpatrick AL, et al. Ginkgo biloba for prevention of Dementia. A randomized controlled trial. JAMA. 2008;300(19):2253-2262.
In this study, 3,069 community volunteers aged 75 years or older with normal cognition (n = 2587) or mild cognitive impairment (MCI) (n = 482) were randomized to receive a twice-daily dose of 120 mg extract of G. biloba (n = 1545) or placebo (n = 1524). This trial was conducted in 5 academic medical centers in the United States between 2000 and 2008 with a median follow-up of 6.1 years.
Participants were assessed every 6 months for incident dementia. Five hundred twenty-three individuals developed dementia (246 from the placebo group and 277 who took G. biloba). And 92% of the dementia cases were classified as possible or probable Alzheimer's disease (AD), or AD with evidence of vascular disease of the brain. Adverse effects were similar for both groups. The overall dementia rate was 3.3 per 100 person-years in the G. biloba group and 2.9 per 100 person-years in the placebo group. The hazard ratio (HR) for G. biloba compared with placebo for all-cause dementia was 1.12 (95% confidence interval [CI], 0.94-1.33; P = .21) and for AD, 1.16 (95% CI, 0.97-1.39; P = .11). There was no effect of G. biloba on the rate of progression to dementia in participants with MCI (HR, 1.13; 95% CI, 0.85-1.50; P = .39).
G. biloba was not beneficial in reducing the overall incidence rate of dementia or incidence of AD in elderly subjects with normal cognition or those with MCI.
The researchers do cite a potential limitation of this study: Because the delay from initial brain changes to clinical dementia involves a long period of time, it is possible it may take several years before the effects of G. biloba are observed.