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TUESDAY, December 29, 2009 (Health.com) — Ginkgo biloba has failed—again—to live up to its reputation for boosting memory and brain function.

Just over a year after a study showed that the herb doesn’t prevent dementia and Alzheimer’s disease, a new study from the same team of researchers has found no evidence that ginkgo reduces the normal cognitive decline that comes with aging.

Should you take ginkgo to slow down the effects of age on the brain? “The answer appears to be ‘no,’” says the lead author of the study, Steven T. DeKosky, MD, the vice president and dean of the School of Medicine at the University of Virginia.

In the new study, the largest of its kind to date, Dr. DeKosky and his colleagues followed more than 3,000 people between the ages of 72 and 96 for an average of six years. Half of the participants took two 120-milligram capsules of ginkgo a day during the study period, and the other half took a placebo.

The people who took ginkgo showed no differences in attention, memory, and other cognitive measures compared to those who took the placebo, according to the study, which was published today in the Journal of the American Medical Association.

Dr. DeKosky also led the 2008 study that looked at the effects of ginkgo on dementia and Alzheimer’s disease. Both studies are part of the larger Ginkgo Evaluation of Memory (GEM) study, which is funded by the National Center for Complementary and Alternative Medicine and the National Institute on Aging.

Ginkgo biloba is among the most popular dietary supplements for brain health. In 2007, Americans spent $107 million on ginkgo, which has been used for more than 1,600 years to promote mental acuity, says Dr. DeKosky. (Ginkgo has also been used to treat a range of maladies including asthma and ringing in the ears.)

When ginkgo first became popular in the 1980s and 1990s, researchers and consumers alike were optimistic about the effects of ginkgo on cognition, but its reputation has suffered in recent years, says Joshua Steinerman, MD, assistant professor of neurology at Montefiore Medical Center in the Bronx, N.Y.

“Early studies seemed to show that there might be some cognitive improvement, but those were typically smaller studies and not as well designed,” says Dr. Steinerman, who did not participate in the current study. “More recent studies, including the GEM study, are large and well controlled, and have showed no consistent positive effect on slowing the rate of cognitive decline.”

Even so, Dr. DeKosky says he and his colleagues were surprised to find that ginkgo failed to produce any benefit, given how long the herb has been used and how many people swear by it. “We figured that if [ginkgo] was still in use and still endorsed by people—even if it’s only your grandmother—it probably does have some basis to it,” he says.

Next page: Other ways to keep your brain healthy