Chicago ? The dietary supplement ginkgo, long promoted as an aid to memory, didn’t help prevent dementia and Alzheimer’s disease in the longest and largest test of the extract in older Americans.

“We don’t think it has a future as a powerful anti-dementia drug,” said Dr. Steven DeKosky of the University of Virginia School of Medicine, who led the federally funded study.

Extracts from ginkgo tree leaves have antioxidant and anti-inflammatory effects, but earlier research on ginkgo and memory showed mixed results. Annual U.S. sales of the supplement reached $107 million in 2007, according to Nutrition Business Journal estimates.

For the new study, appearing in today’s Journal of the American Medical Association, researchers recruited more than 3,000 people, ages 75 and older, from voter and mailing lists in Maryland, Pennsylvania, California and North Carolina.