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WASHINGTON (Reuters) - The widely used herbal supplement Ginkgo biloba does not appear to prevent Alzheimer's disease in healthy elderly people or those with mild cognitive impairment, U.S. researchers said on Tuesday.
The study involved 3,069 people age 75 or older at five U.S. locations who were tracked for six years on average, half taking twice-daily doses of 120 milligrams of extract from the leaves of the ginkgo tree and the rest taking a placebo.
Those who took the ginkgo were no more or less likely to develop Alzheimer's or any type of dementia, the researchers wrote in the Journal of the American Medical Association.
Dr. Steven DeKosky, dean of the University of Virginia School of Medicine who led the study, said he was disappointed in the results, citing early indications that ginkgo has antioxidant and other properties that might preserve memory.
"At this point in time, I wouldn't tell anybody to take the medication in hopes that it would work (to prevent Alzheimer's)," DeKosky, who was at the University of Pittsburgh when the study was conducted, said in a telephone interview.
"If they want to continue taking it -- because it's not toxic and not expensive -- they probably aren't going to hurt themselves other than spending the money," DeKosky added.
Ginkgo is one of the top-selling herbal supplements, used by people with the aim of improving memory and cognition and other purposes. This was the largest and most rigorous study to date on whether it would stave off Alzheimer's, experts said.
The people entered the study with either no cognitive problems or only mild impairment. Eighteen percent in the ginkgo group and 16 percent in the placebo group were diagnosed with Alzheimer's or other dementia during the study.
DeKosky said he could not rule out that ginkgo might have shown some benefit in preventing Alzheimer's if the study had gone on longer because progression from initial brain changes to clinical dementia takes many years.
There is no medication currently approved to avert the development of Alzheimer's disease, the most common form of dementia in the elderly.
Dr. Murali Doraiswamy of Duke University Medical Center in Durham, North Carolina, noted that other Alzheimer's prevention failures include statins, estrogen, anti-inflammatory drugs, vitamin E and drugs called cholinesterase inhibitors.
Doraiswamy, a memory expert who was not part of the study, said the findings will lead him to actively discourage people from taking ginkgo with the aim of preventing Alzheimer's.
Alzheimer's is incurable. It slowly progresses from mild memory loss to severe brain damage and death. It is expected to become even more common as populations age in many countries.
"Alzheimer's, by its very nature, tends to breed desperation, and that will direct some people to try almost anything. Here, at least, we have some evidence that it's probably worth your while to find something else than ginkgo," Bill Thies of the Alzheimer's Association advocacy group said.
Industry groups took issue with the study.
Michael McGuffin of the American Herbal Products Association said the findings do not undermine earlier evidence that ginkgo is useful in relieving symptoms in people who already have Alzheimer's.
Daniel Fabricant of the Natural Products Association said a study starting when people are in middle age rather than almost 80 would be the best way to analyze Alzheimer's prevention.
The ginkgo product used in the research was made by German-based Schwabe Pharmaceuticals.
Editing by Vicki Allen