The research subjects, nearly all under 40, were given doses of ginkgo biloba and then tested for mental performance. Several of the studies tested for improvements in short-term memory (memory of recent events). Several also measured reaction time to gauge overall mental sharpness. Several studies even measured brain-wave patterns-a test called an electroencephalogram, or EEG-to detect the impact of ginkgo on brain chemistry.
The key question is whether these studies prove that ginkgo biloba boosts brain function in essentially normal people who experience relatively minor memory slips or may simply want to function at their peak. "The evidence on that is extremely scanty, just a few small studies that seemed to indicate some improvement," says Varro E. Tyler, an emeritus professor of pharmacy at Purdue University. "Ginkgo may be helpful, but we need more proof than that." Tyler is the author (with Steven Foster) of a layperson's guide to herbal remedies, Tyler's Honest Herbal, which is based on published scientific studies. Tyler has reviewed the studies of ginkgo biloba and mental performance, and he is not convinced.
One reason for his skepticism is the relatively small number of people involved in the studies. Indeed, four of the six studies on "normal" brains cited by Pharmaton involved a dozen people or less. Decades of drug research has shown that positive results from small studies frequently evaporate when the drugs are tested in large and diverse populations of people.
"The literature is full of reports of a small number of patients who had a remarkable improvement taking drug X or treatment Y, and then when you do a large trial you find there's no effect," says Steven DeKosky, a researcher at the University of Pittsburgh School of Medicine who is conducting a major new study of ginkgo for Alzheimer's disease.
Basically, the studies of ginkgo and the normal brain evaluate whether the herb is a "cognitive enhancer," a substance that maintains and even improves concentration, memory, and other skills. The researchers measured certain aspects of mental function, such as reaction time and short-term recall. For example, a 1986 study listed by Pharmaton measured the effect of ginkgo on short-term memory in 8 female volunteers. Among other tests, the women took a Sternberg memory scan. The Sternberg test measures how fast a person can recall items from a memorized list. As reported in the French medical journal, Presse Medicale, the people who took ginkgo performed better on the test than those who didn't.
But even if the handful of studies on ginkgo and mental performance hold up, the evidence they provide doesn't necessarily back up the claims made by ginkgo manufacturers.
To a fan of ginkgo biloba, scoring higher on the Sternberg memory scan would prove that the herb improves mental performance. But keep in mind that in real life, people aren't called upon to perform the Sternberg memory scan. What we really want to remember are things like lunch dates, a grandchild's birthday, and the names of people we were introduced to at a party. Better performance on laboratory psychological tests doesn't guarantee that people will perform better on complex and demanding memory tasks in the real world.
Of course, the studies mentioned above are not the sum total of all ginkgo research. Ginkgo biloba has also been tested extensively on older people experiencing age-related impairments, as well as people with Alzheimer's disease. These studies, however, have been criticized for flaws that cast serious doubts on their results. An upcoming issue of Memory Loss & the Brain will examine the record in more detail and highlight some new studies that may help settle the issue of ginkgo and Alzheimer's disease. But even if ginkgo does help ease mental impairments due to aging or disease, that does not mean it will enhance the performance of a brain already functioning normally. "It may well do that in some way, but we can't say that it does," Varro Tyler says. "The advertisements that say that it does are exaggerations, unsupported extrapolations."
Truth in Labeling?
Tyler and DeKosky are not alone in their skepticism. Their opinions echo those of many other researchers and physicians familiar with ginkgo research. The evidence to date, they say, is just not convincing enough to warrant the claims made on the labels of ginkgo biloba supplements. That raises an obvious question: If the jury is still out on ginkgo and the brain, how can supplement manufacturers legally make the claims they do? The short answer is this: because the U.S.
Congress passed the Dietary Supplement Health and Education Act in 1994. This law allows supplement manufacturers to make general statements about the health-promoting properties of ginkgo biloba and other dietary supplements. What they cannot do is make specific "health claims" that the product treats, diagnoses, cures or prevents disease. Labels can say that ginkgo "enhances memory" but cannot say that ginkgo "decreases memory loss due to Alzheimer's disease." Without this legal re-classification of herbal remedies as dietary supplements, ginkgo would have been considered a drug or a food additive. And that means ginkgo products would have been held to the U.S. Food and Drug Administration's strict standards for safety and effectiveness.
Lacking large, well-done studies of the effect of ginkgo biloba on normal mental function, the claims made by ginkgo manufacturers are still speculation. And the harmful side-effects of taking ginkgo, if there are any, remain unknown. Right now, the controversy over ginkgo and the brain is very much like a jury trial still in progress, with lots of evidence presented but nothing convincing enough for a final verdict.