For years, practitioners of alternative medicine have been touting the benefits of ginkgo, especially for maintaining brain health, but a new study finds that the centuries-old nostrum does little to slow the cognitive decline of aging.
Researchers at six universities across the U.S., led by Dr. Steven DeKosky at the University of Virginia School of Medicine, report that elderly people taking ginkgo supplements showed no notable differences in scores on brain-function tests from people taking placebo pills. The team, which published its results Tuesday, Dec. 29, in the Journal of the American Medical Association, tested volunteers on a range of tasks, including memory, attention, language, and visual and spatial constructions, and found that the extract from the ancient tree did little to slow the decline of these functions.
"For me, this kind of closes the book on whether or not, if you start taking ginkgo later in life, you are going to have cognitive benefit," says DeKosky, vice dean of the School of Medicine. "We don't have good evidence that it maintains good brain health."
The study is the largest and, with a mean follow-up of six years, also the longest to investigate the effects of ginkgo on the brain. An earlier analysis, also led by DeKosky, reported in 2008 that ginkgo supplements do not prevent the development of dementia or Alzheimer's disease in older people. Taken together, the two evaluations strongly suggest that ginkgo does little, if anything, to improve acuity in cognitive functions such as memory, language, and visual and spatial orientation.
Scientists had thought ginkgo extract might work as an anti-inflammatory agent to keep brain connections healthy and promote steady flow of nutrients to neurons. They also thought ginkgo, a strong antioxidant, helped inhibit oxidative damage to brain neurons caused by free radicals found in pollutants or made as a by-product of many metabolic processes. But if ginkgo were working in this way, says DeKosky, he and his team would almost certainly have detected a difference between the treatment and placebo groups.
As it was, the more than 3,000 elderly volunteers between the ages of 72 and 96 were tested repeatedly using crude screening measures as well as more detailed, computerized assessments of their mental function. Over the years, researchers saw overall cognitive decline in the study participants. The average rate of change in performance on the tests, which were initially given every six months and then yearly, was similar for both the ginkgo and placebo groups. "Quite frankly, one of the things that surprised us was that for an extract that has been around for this long, there ought to be a signal of some sort, or we ought to see some effect for it to have maintained its reputation for so long," says DeKosky. "And we didn't."
DeKosky admits that the study has its limitations the subjects were more than 70 years old, and it's not clear whether ginkgo's effect on the brain may be more profound if introduced earlier. Then there is the question of exactly how ginkgo is acting on the body; if the compound works by improving circulation not just in the brain but throughout the body, for example, then this study may not have been refined enough to pick up those subtle, more indirect effects. "What we would really like to see is additional research," says Douglas MacKay, vice president of scientific and regulatory affairs for the Council for Responsible Nutrition, a leading trade organization of dietary-supplement makers. "What we would not like to see is this study closing the door on answering other questions or subsets of questions on ginkgo." The bar, however, for those additional studies seems to be getting higher.