TUESDAY, Nov. 18 (HealthDay News) — Although commonly taken to improve memory, new research suggests that the herb ginkgo biloba won’t help prevent dementia, including Alzheimer’s disease.

“We found that giving a standardized dose of ginkgo biloba over a period of time does not slow down the incidence rate of dementia or Alzheimer’s disease,” said the study’s lead author, Dr. Steven DeKosky, who was chair of the department of neurology at the University of Pittsburgh School of Medicine and Medical Center at the time of the study.

The findings were published in the Nov. 19 issue of the Journal of the American Medical Association.

Dementia, including Alzheimer’s disease, currently affects about 5 million people in the United States, according to background information in the article. Dementia is a significant cause of age-related disability and the need for long-term nursing home care, the study reported.

There are currently no medications that have been approved for the primary prevention of dementia or Alzheimer’s disease. However, previous small, short-term clinical trials have suggested there might be a small benefit from ginkgo for people with dementia. Sales of ginkgo biloba are almost $250 million each year in the United States, according to the study.

The current study included almost 3,100 community-dwelling adults aged 75 or older. Most had normal cognition at the start of the study, while 482 had mild cognitive impairment when the study began.

The study volunteers were randomly assigned to receive either a twice-daily dose of 120 milligrams of ginkgo biloba extract or a twice-daily placebo. The study participants were assessed for signs of dementia every six months, and the average length of study participation was just over six years.

During the study period, 523 people developed dementia, and 92 percent of those cases were classified as possible or probable Alzheimer’s disease.

Overall, the dementia rate for those taking ginkgo was 3.3 per 100 person-years of follow-up versus 2.9 per 100 person-years for the placebo group.

“If you’re in your 70s or 80s, and you’re contemplating taking ginkgo to prevent Alzheimer’s or dementia, the idea that it can prevent these is not true,” said DeKosky, who is vice president and dean of the University of Virginia School of Medicine in Charlottesville.

But, said DeKosky, the good news from this study is that there appear to be “no major problems for safety” where ginkgo is concerned.

However, the author of an accompanying editorial in the same issue of the journal, Dr. Lon Schneider, director of the State of California Alzheimer’s Disease Research and Clinical Center at the University of Southern California in Los Angeles, pointed out that for people with a history of cardiovascular disease, there was an increased risk of hemorrhagic stroke in the group taking ginkgo, though the difference didn’t reach statistical significance. Eight people in the placebo compared to 16 in the ginkgo group had a hemorrhagic stroke, Schneider noted.

He also pointed out that at least one smaller trial found an increased risk of the more common type of stroke, ischemic stroke, and transient ischemic attacks, in people taking ginkgo.

“In the absence of efficacy, people should be fairly careful about taking a drug anyway, and here, we’ve seen no evidence for potential gain, and there’s some reason to be concerned about its use in the long term,” said Schneider.