November 6, 2008
Millions of older Americans take the herb ginkgo biloba in the hopes of warding off senior moments and the onset of Alzheimer's disease as well. But a rigorous new study involving thousands of seniors found that supplements containing the herb did nothing to ward off the onset of the memory-robbing ailment.
The study, from researchers at five medical centers across the country, involved more than 3,000 men and women aged 75 and older. Most were mentally intact at the start of the study, in 2000, though some in each group had mild cognitive impairment, a form of memory loss that is far less severe than Alzheimer's but which may progress to Alzheimer's with time.
Participants were divided into two groups. Half took ginkgo, at a dose of 120 mg twice a day, for an average of six years. The others took a look-alike placebo. All were given memory tests and check-ups at six-month intervals to look for signs of Alzheimer's disease. Brain scans were also performed if it was suspected that someone might have Alzheimer's.
The researchers found that by the time the study was completed, in 2008, there was no difference in the rates of Alzheimer's onset between the group taking ginkgo and the group taking a placebo. Of the 3,069 people in the study, 523 were given a diagnosis of Alzheimer's or another form of dementia over the course of the study. Dementia developed in 246 of those receiving placebo, compared to 277 in the ginkgo group.
Ginkgo is a potent antioxidant that, in laboratory studies, helps to protect cells grown in a dish against damage from reactive oxygen molecules. It is thought that antioxidant protection of the cells in the brain may help protect against Alzheimer's and other forms of dementia. Some studies suggested that ginkgo may have protective activity against beta-amyloid, a toxic protein that builds up in the brains of those with Alzheimer's.
The trial, called the Ginkgo Evaluation of Memory, or GEM study, was the largest to date to evaluate the herb. The findings were published in the Journal of the American Medical Association.
"Despite early indications that ginkgo biloba has antioxidant and other properties that might preserve memory, this trial shows that, in fact, it has no impact on development of dementia and Alzheimer's disease," said lead investigator Dr. Steven T. DeKosky, director of the University of Pittsburgh Alzheimer's Disease Research Center and Chair of the Department of Neurology at the time the study was conducted.
In the study, ginkgo also did not have any benefits against coronary heart disease or stroke. The researchers note that it's possible that an effect would have been observed if the study had gone on longer, because it takes many years to progress from initial brain changes to clinical dementia. Therefore, the research team intends to conduct a follow-up analysis of brain function and structure in a subset of participants using magnetic resonance imaging.
In Europe and other parts of the world, physicians often prescribe ginkgo biloba to help ward off memory loss. However, there are no medications approved for the prevention of Alzheimer's disease. Current drugs for the disease may help ease symptoms for a time but do little to stop the downward progression of disease.
"Based on the results of this trial, Ginkgo biloba cannot be recommended for the purpose of preventing dementia," the authors wrote. "These results confirm that randomized trials remain critical to the spectrum of research necessary to develop new therapies."
In an editorial accompanying the study, Dr. Lon S. Schneider of the University of Southern California in Los Angeles commented on the uncertainty surrounding the hugely popular herbal supplement ginkgo biloba, which had sales of $247 million last year in the United States alone.
"Despite two decades of research with standardized extracts of ginkgo biloba, considerable uncertainty about its pharmacology and clinical effects remains," Dr. Schneider said. "The GEM study adds to the substantial body of evidence that ginkgo biloba extract as it is generally used does not prevent dementia in individuals with or without cognitive impairment and is not effective for Alzheimer's disease."
Earlier research has suggested the ginkgo may have benefits for the brain, though results have been mixed. Earlier this year, for example, a small study from the Oregon Health & Sciences University in Portland suggested that the herb might help prevent elderly men and women from developing mild cognitive impairment. But the study was small, done in only 118 seniors. It also found that people taking ginkgo biloba were more likely to have a stroke or "mini-stroke" (transient ischemic attack), raising concerns about the safety of the herb.
However, other studies involving hundreds of patients and lasting about 6 months showed that gingko biloba did ease Alzheimer's symptoms, including psychiatric symptoms of the disease. Although the current study was well designed and gave compelling results, it still appears that there is uncertainty as to whether gingko biloba may be of benefit in Alzheimer's disease.
Experts caution that anyone taking ginkgo or products containing the herb should let their doctors know. It may interact with prescription or over-the-counter medications, including aspirin and warfarin, raising the risk of dangerous bleeding. In the current study, people who were taking blood-thinners or who had other blood conditions were excluded from the study.
Steven T. DeKosky, M.D.; Jeff D. Williamson, M.D., M.H.S.; Annette L. Fitzpatrick, Ph.D., et al: "Ginkgo biloba for Prevention of Dementia: A Randomized Controlled Trial." Journal of the American Medical Association, November 19, 2008, Volume 300, Number 19, pages 2253-2262.
Lon S. Schneider, M.D.: "Ginkgo Biloba Extract and Preventing Alzheimer Disease" (editorial). Journal of the American Medical Association, November 19, 2008, Volume 300, Number 19, pages 2306-2308.