Gingko Biloba (also spelled ginkgo) is the world’s bestselling herbal dietary supplement, primarily because of the widespread claim that it will enhance memory and ward off the effects of senile dementia. The supplement is an extract from the leaves of the plant that has been used in Asia for thousands of years to treat cardiovascular problems and lung complaints. Its use for these purposes is unsurprising, since gingko is known to act as a vasodilator, causing the dilation of blood vessels, especially capillaries and microcapillaries. This, along with its anticoagulant effect, could well make it useful for improving circulation, although very little well designed research exists to conﬁrm this. Its claimed effects on memory and cognitive performance appear to follow logically enough: if blood ﬂow to the brain areas involved in memory is improved, this could legitimately be expected to improve memory function.
Numerous studies have been undertaken to examine gingko’s potential as a treatment for Alzheimer’s disease, but results have been mixed, and some serious ﬂaws limit the interpretability of the results. A 1997 study published in the Journal of the American Medical Association, for example, found a slight improvement in cognitive functioning and mood in Alzheimer’s patients given daily doses of gingko. Only about 60 percent of the participants completed the study, however, which could distort the ﬁndings signiﬁcantly. Furthermore, the effect observed was quite small, and this study and others like it have dealt only with improvement of functioning, not the exaggerated claims about delay of onset and prevention that are found in many locations on the Internet.
Given the data supporting a slight improvement in functioning in Alzheimer’s patients, the marketers of herbal supplements have been quick to present gingko biloba as a useful memory aid for healthy younger adults as well. In studies on these effects, the results are less impressive. Paul Solomon and his colleagues recently conducted a trial in which 230 adults aged sixty or over received either gingko or a placebo three times daily for six weeks. The dose used was that recommended by the supplement manufacturer, and a six-week period was chosen because the same manufacturer promised results within four weeks. The results showed no difference between gingko and the placebo on fourteen different measures of cognitive function and memory. Furthermore, there was no difference found in the participants’ own subjective self-report of memory improvement.
Although it may have a small effect on functioning in patients with senile dementia, the claim that gingko biloba will in any way enhance memory in healthy adults is simply not supported by evidence. More troubling are the possible side effects of gingko, especially in elderly patients who already take daily doses of aspirin or other anti-coagulants or have a prior history of high blood pressure or stroke. The modest improvement in memory function may not be worth the slightly increased risk of cerebral bleeding or stroke.
- Le Bars, P. L., Katz, M. M., Berman, N., Itil, T. M., Freedman, A. M., and Schatzberg, A. F. “A Placebo-Controlled, Double-Blind, Randomized Trial of an Extract of Ginkgo Biloba for Dementia.” Journal of the American Medical Association, 278 (1997): 1327–1332;
- Solomon, P. R., Adams, F., Silver, A., Zimmer, J., and DeVeaux, R. “Ginkgo for Memory Enhancement: A Randomized Controlled Trial.” Journal of the American Medical Association, 288 (2002): 835–840.