Companies also say it promotes blood circulation to the arms, legs and brain, thereby boosting overall physical activity levels. Americans spent $107 million on ginkgo biloba products last year, according to Nutrition Business Journal.
"People tell me, 'I took ginkgo, and I could focus for three hours -- I never got up to get coffee,' " Blumenthal said. "I get too wired on it myself."
Ginkgo biloba contains flavonoids, whose antioxidant properties have been shown to combat the chemical damage that accumulates in aging brain cells. One laboratory study also found that ginkgo extract prevents the accumulation of beta-amyloid proteins which cluster into plaque in the brains of Alzheimer's patients.
"There are a lot of purported reasons why ginkgo might work," said Richard L. Nahin, a neuroscientist at the National Center for Complementary and Alternative Medicine, who worked on the study.
Small scientific studies of the herb have produced mixed results. Ginkgo appeared to help patients with dementia and Alzheimer's in some clinical trials, but others found it had no effect.
The latest study, funded primarily by the NIH, focused on elderly men and women who had normal mental function or only mild cognitive impairment. They were recruited from voter registration rolls and private mailing lists in four areas served by large academic hospitals: Sacramento; Pittsburgh; Hagerstown, Md.; and Winston-Salem and Greensboro, N.C.
Of the 3,069 people who enrolled in the study, 1,545 took 240 milligrams a day of the ginkgo extract EGb 761, the variety used in Ginkgold products sold by Nature's Way. The other 1,524 participants took identical-looking placebos. All the pills were supplied by Schwabe Pharmaceuticals, a large supplement maker in Germany.
By the end of the study, 277 people who took ginkgo, or 18%, were diagnosed with dementia, compared with 246, or 16%, in the placebo group, according to the study. The ginkgo group also included 257 cases of Alzheimer's, versus 220 in the placebo group. None of those differences was statistically significant, the researchers said.
There was also no difference in the rate of strokes, heart attacks and other cardiovascular events between the two treatment groups.
The only solid distinction between the two groups was the rate of patients developing a condition known as vascular dementia but not Alzheimer's -- 0.2% among in the ginkgo group and only 0.08% among the controls. Vascular dementia occurs when blood flow to the brain is restricted, often by a stroke.
