Ginkgo biloba has been used medicinally for thousands of years. Today, it is one of the top selling herbs in the United States. It is not clear how many people take the drug, but its sales exceeded $249 million in 2006.

Ginkgo is used for the treatment of numerous conditions, many of which are under scientific investigation. Available evidence demonstrates ginkgo’s efficacy in the management of intermittent claudication, and “cerebral insufficiency” (a syndrome thought to be secondary to atherosclerotic disease, characterized by impaired concentration, confusion, decreased physical performance, fatigue, headache dizziness, depression and anxiety).

Although not definitive, there is promising early evidence favoring the use of ginkgo for memory enhancement in healthy subjects, altitude (mountain) sickness, symptoms of premenstrual syndrome (PMS), and reduction of chemotherapy-induced end-organ vascular damage.

Ginkgo biloba was also thought to be effective in preventing or slowing the progression of Alzheimer’s disease and other age-related dementias, but one of the largest and longest studies to address the issue shows no benefit.

The study was published in the Nov. 19 issue of The Journal of the American Medical Association. It involved 3,069 people aged 75 or older. About half of them were given 120 milligrams of ginkgo biloba twice a day while the other half were given a placebo. Neither the patients nor the researchers knew which treatment was being given.

After sixe years, 523 study participants were diagnosed with dementia, 246 (16 percent) in the placebo group and 277 (18 percent) in the ginkgo group. The rate of Alzheimer’s disease did not differ significantly between the two groups, with 3.3 cases occurring for every 100 people treated with gingko biloba each year, compared to 2.9 cases in the placebo group. The study also found no effect on the progression of mild cognitive impairment to dementia.

“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.

This is not the first study showing that ginkgo biloba is not exactly the best option for slowing Alzheimer’s progression. Back in February, a three-year study by researchers at the Oregon State University published in the journal Neurology revealed that the herbal supplement said to enhance memory did not offer protection against memory loss in octogenarians. Moreover, the participants taking gingko biloba appeared to be more likely to have a stroke or mini stroke. The researchers then noted that while further research is needed for an unambiguous conclusion on the effects of the herbal supplement, its wide availability, inexpensiveness and wide use among people pose questions regarding its safety.

Alzheimer’s disease causes a progressive loss of memory and mental faculties, which can be devastating for the patients concerned and those around them. About 5.2 million Americans live with the brain disorder, a number that is expected to grow as the baby boom generation ages. About 16 million people are forecast to have Alzheimer’s by 2050, as existing drugs can ease symptoms but do not stop the disease from developing. The disease already afflicts one in eight people 65 and older and nearly one in two people over 85.

The best way to prevent dementia is to have a balance in your life. Dekosky says that what’s good for the heart is also good for the head; thus a healthy diet and exercising as much as possible are important in keeping the brain sharp.