In late August, The Journal of the American Medical Association published a study that found that Ginkgo biloba does not enhance memory or improve cognitive function. Previous research has indicated that the botanical improves cognitive function and memory in elderly individuals with mild to moderate mental impairment.
In the JAMA study, psychologist Paul R. Solomon, Ph.D., of Williams College in Williamstown, Mass., conducted a six-week randomized, double-blind clinical trial to determine whether ginkgo could improve memory, attention and related cognitive functions in as short a time as four weeks. Solomon gave 230 elderly study participants with unimpaired mental function either 40 mg of ginkgo three times daily or a placebo.
Solomon conducted neuropsychological tests for learning, memory, attention, concentration, naming and verbal fluency, and concluded that ginkgo did not enhance performance more than placebo.
Phil Harvey, Ph.D., director of science and quality assurance for the National Nutritional Foods Association in Newport Beach, Calif., criticized the study's short length and dosage. "You may not see changes in a six-week trial involving a healthy group. The changes may be seen over a longer period of time," Harvey said. "Also, the dosage may not have been therapeutic enough for certain individuals to take effect. It is possible that some people would have benefited from taking higher amounts of the herb."
Industry associations also responded by citing previous studies that support the herb's ability to boost memory.
"There are more than 125 clinical trials published on ginkgo extract over the past two decades, with most of them supporting numerous important benefits related to improved circulation and mental function," said Mark Blumenthal, founder and executive director of Austin, Texas-based American Botanical Council. "The value of ginkgo or any dietary supplement cannot be determined on the basis of one study alone."
Another six-week randomized, double-blind, placebo-controlled study of ginkgo that was published in August in The Human Psychopharmacology: Clinical and Experimental found that the herb did improve memory, attention and cognitive clarity in adults with normal mental function. However in this study, participants took 60 mg more of ginkgo each day than in the JAMA study.
The NNFA's Harvey called for a meta-analysis, or a systematic review, of all the clinical studies on ginkgo to evaluate the botanical's overall effectiveness. "We're looking at things through a microscope rather than at the big picture," Harvey said. "We need to look at all the studies to find out what the majority of the studies [indicate] rather than just listening to this one JAMA study saying that ginkgo is ineffective and thinking that's the final word."
Currently, the Cochrane Collaboration, an international organization of scientists who review research, has proposed to conduct a meta-analysis on ginkgo.
Natural Foods Merchandiser volume XXIII/number 10/p. 5