A new study finds that Ginkgo biloba, an herb that some advocates claim helps memory and cognition, was not effective in reducing the rate of dementia or Alzheimer's disease among more than 1,500 elderly study participants after several years of use.

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

Dementia, especially Alzheimer’s disease, affects more than 5 million people in the United States and is a leading cause of age-related disability and long-term care placement, the article says.

And while Ginkgo biloba is prescribed in some areas of the world for preservation of memory, no robust clinical trials of the herb existed, the JAMA article said.

"Any change in the thinking function that occurred over time in the people we studied, we were interested in diagnosing accurately and determining whether Ginkgo made a difference in the people who developed dementias and those who did not," said Dr. Steven T. DeKosky of the University of Virginia School of Medicine. "The main finding of the study was that using Gingko biloba over the course of an average of 5 to 6 years did not seem to affect the number of people who developed dementia or Alzheimer’s disease over the period of the study."

The clinical trials took place at five academic medical centers in the United States between 2000 and 2008, and were followed up about six years later. The study group comprised 3,069 volunteers aged 75 years or older with normal cognition, or mild cognitive impairment.

Based on the results of this trial, Ginkgo biloba cannot be recommended for the purpose of preventing dementia, the authors said.