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TUESDAY, Nov. 18, 2008 (Health.com) — 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 trials—until now—have thoroughly evaluated the safety and effectiveness of ginkgo biloba extract as a way to prevent dementia.

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.

“I’m disappointed,” says lead study author Steven DeKosky, MD, 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.” (Dr. DeKosky was chair of the department of neurology at the University of Pittsburgh at the time of the study.)

More than five 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% of patients with memory loss and other mental ability problems. Dr. 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.

Next: Is it safe to take ginkgo?