The popular herb ginkgo biloba does not reduce the risk of dementia or Alzheimer's disease, according to a study of more than 1,500 elderly patients who took the supplement. Often touted as a way to preserve aging memories, no large-scale, randomized clinical trial -- until now -- has thoroughly evaluated the safety and effectiveness of ginkgo biloba extract as a way to prevent dementia.

Ginkgo extract sales reached $107 million in 2007, according to the Nutrition Business Journal.

In the new government-funded study, volunteers ages 75 and older with either normal mental function or mild cognitive impairment took a twice-daily placebo or ginkgo biloba extract (for a total of 240 milligrams per day).

The researchers tested the volunteers' memory and other mental abilities every six months for about six years. Ginkgo supplements were no better than a placebo for preventing dementia, according to the study, which was sponsored by the National Center for Complementary and Alternative Medicine and the National Institute on Aging of the National Institutes of Health. It appears in the November 19 issue of the Journal of the American Medical Association.

"I'm disappointed," says lead study author Steven DeKosky, M.D., vice president and dean of the University of Virginia School of Medicine. "It would've been wonderful to find something relatively well known and inexpensive that might have been helpful and protective." DeKosky was chair of the department of neurology at the University of Pittsburgh, in Pennsylvania, at the time of the study. Why these energy boosters are poor substitutes for sleep

More than 5 million people in the United States have Alzheimer's disease, according to the Alzheimer's Association. It's the most common form of dementia and affects somewhere between 60 to 80 percent of patients with memory loss and other mental ability problems. DeKosky says the number of people who will be affected by dementia may triple in the next 20 to 30 years as the baby boom generation ages.

Ginkgo extracts are derived from the leaves of the Ginkgo biloba tree; they contain substances called flavonoids and terpene lactones, which have appeared promising in laboratory studies for the prevention of Alzheimer's disease. However, results in humans have been mixed, at best. Despite that mixed record, ginkgo extract sales reached $107 million in 2007, according to the Nutrition Business Journal. Eight natural remedies that may help you sleep

DeKosky says that there were two important conclusions to take away from the study: Ginkgo biloba is ineffective in battling dementia, but also that the herb is relatively safe. Still, some research has suggested that it may cause excessive bleeding.

In the new study, people taking ginkgo were more likely than placebo users to have a bleeding-related stroke (16 events with ginkgo versus eight with placebo). However, the results were not statistically significant and may have been due to chance.

Because of the potential for unknown side effects, "it is untenable to recommend a drug or nutraceutical in the absence of efficacy evidence simply because it could possibly help and initially appears harmless," Lon S. Schneider, M.D., of the University of Southern California, Los Angeles, said in an editorial accompanying the study.

Others in the medical community agree that the supplement doesn't seem to be worthwhile.

"I don't think there is a role for ginkgo biloba in human health at this point," says Gary J. Kennedy, M.D., director of geriatric psychiatry at Montefiore Medical Center in New York. "This study was long enough that if ginkgo had any protective capacity to prevent Alzheimer's or slow cognitive decline, it would have shown it."

The best way to prevent dementia is to keep the mind active, whether it's by reading books, doing crossword puzzles, playing sudoku, or participating in other creative endeavors, says Kennedy. All antidepressants work the same, but some pricier than others

DeKosky also says that what's good for the heart is good for the head; thus, diet and exercise are also important in keeping the brain sharp.

"I would have loved to have [ginkgo extracts] work. Even if it slowed things down by 20 percent, that's a huge number, when you multiply it by the millions of people who have [Alzheimer's] disease or are at risk for it," says DeKosky. "We didn't do this study just to prove that something didn't work."

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The Natural Products Association (NPA), which represents ginkgo manufacturers, released a statement that said the new research can't be used to make broad conclusions because the average age of the participants was nearly 80, and the findings may not apply to the general population.

"I still think there is great promise for ginkgo biloba," says Daniel Fabricant, Ph.D., the vice president of scientific and regulatory affairs at the NPA.

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All About Alzheimer's Disease • Herbal Medicine