A few months ago, I posted on the results of some large-scale trials of ginkgo biloba and memory (“Gingko and memory: Not so fast”). Ginkgo is one of the best-selling herbal products in the US, targeted at individuals who want to stave off Alzheimer’s disease or simply maintain better memory function. Until now, there has been little proof of these claims: several large, well-designed, federally-funded studies have all shown that healthy people who take ginkgo for several months show no better memory than people taking an inactive placebo; neither does ginkgo appear to protect against development of Alzheimer’s disease.
One counterargument often made by those who believe in ginkgo’s beneficial effects is that these studies were simply too short, and that the benefits of ginkgo only emerge if taken over a period of years.
Now, a new report seems to lay even that objection to rest.
Published in the prestigious Journal of the American Medical Association (JAMA) in December 2009, this latest study followed over 3000 non-demented elderly individuals, randomly assigned to take either ginkgo or placebo twice daily. Importantly, this was a double-blind study, meaning that during the study, neither the participants nor the researchers who evaluated them knew which individuals were taking which type of pill. This procedure prevents the participants and researchers from (even inadvertently) allowing their beliefs about ginkgo’s efficacy, or lack thereof, from influencing the results.
Participants were followed for a median of over 6 years, and checked for rates of change on various cognitive measures, including tests of memory, attention, and executive function. Unsurprisingly, the participants on placebo showed a mild annual decline on these measures – but the participants on ginkgo showed just as much decline.
The researchers also conducted genetic testing, particularly for presence of the APOE-E4 allele, a naturally-occurring genetic variant that increases a person’s risk for developing Alzheimer’s. Some have suggested that, perhaps, the protective effects of ginkgo depend on whether an individual carries this genetic variant. But, again, the results of this long-term study showed no evidence of any beneficial effects, either on carriers or non-carriers of the APOE-E4 allele.
In sum, long-term usage of ginkgo had little or no effect on protecting against memory decline in non-demented elderly individuals. As of now, the bulk of scientific evidence points overwhelmingly in the same direction: arguing against any beneficial effects of ginkgo biloba, either in protection against cognitive decline, or in protection from Alzheimer’s, or in improving memory function in individuals who already have Alzheimer’s.
Further Reading:
B. E. Snitz and others (2009). Ginkgo biloba for preventing cognitive decline in older adults: A randomized trial. In Journal of the American Medical Association (JAMA), vol. 302, no. 24, pp. 2663-2670.
