Studies on the therapeutic effects of Ginkgo biloba
While there is still no cure for Alzheimer's Disease, Ginkgo biloba
has been touted in the market for decades as an effective phytomedicine to prevent this fatal disease. This claim was considered unsupported until the studies in 1990's demonstrated that Ginkgo biloba leaf extract could indeed have therapeutic potential in slowing Alzheimer's Disease [Hofferbach, B. (1994) The efficacy of EGb 761 in patients with senile dementia of the Alzheimer type: A double blinded, placebo-controled study on different levels of investigation. Hum.
Psychopharmacol. 9:215-222.], and in early stages of Alzheimer's Disease [Kanowski, S. et al. (1997) Proof of the efficacy of the Ginkgo biloba special extract EGb 761 in outpatients suffering from mild to moderate dimentia of the Alzhiemer's type or multi-infarct demnetia. Phytomedicine 4(1):3-13.]. Recent studies such as Le Bars et al.
, DeFeudis and Drieu
, Stough et al.
, McKenna, Jones, and Hughes
, Watanabe et al.
, and Wettstein
confirmed previous observations of beneficial effects of Ginkgo biloba phytochemicals on Alzheimer's Disease. Although the seeds of Ginkgo biloba have been most commonly employed in traditional Chinese medicine, in recent years standardized extracts of the leaves have been widely sold as a phytomedicine in Europe and as a dietary supplement in the United States. The primary active constituents of the leaves include flavonoid glycosides and unique diterpenes known as ginkgolides; the latter are potent inhibitors of platelet activating factor. Clinical studies have shown that ginkgo extracts exhibit therapeutic activity in a variety of disorders including Alzheimer's disease, failing memory, age-related dementias, poor cerebral and ocular blood flow, congestive symptoms of premenstrual syndrome, and the prevention of altitude sickness. Due in part to its potent antioxidant properties and ability to enhance peripheral and cerebral circulation, ginkgo's primary application lies in the treatment of cerebrovascular dysfunctions and peripheral vascular disorders [McKenna DJ, Jones K, Hughes K. (2001) Altern Ther Health Med. 7(5):70-86, 88-90.] After all, Ginkgo biloba's beneficial role in Alzheimer's Disease appear to be more than just a hype, although by no means it is a cure.
Research in the United States
Researchers at the New York Institute for Medical Research in Tarrytown, New York, conducted the first clinical study of ginkgo biloba and dementia in the United States. Their findings were published in the Journal of the American Medical Association (October 22/29, 1997). These scientists examined how taking 120 mg a day of a ginkgo biloba extract affected the rate of cognitive decline in people with mild to moderately severe dementia due to Alzheimer's Disease and vascular dementia. At the end of the study, they reported a small treatment difference in people given the ginkgo biloba extract.
Three tests were used to measure changes in the condition of participants. First, participants showed a slight improvement on a test that measured their cognitive function (mental processes of knowing, thinking, and learning). Second, participants showed a slight improvement on a test that measured social behavior and mood changes that were observed by their caregivers. Third, participants showed no improvement on a doctor's assessment of change test.
Because 60 percent of the people did not complete the study, findings are difficult to interpret and may even be distorted. In addition, this study did not address the effect of ginkgo biloba on delaying or preventing the onset of Alzheimer's Disease or vascular dementia. The researchers recommend more investigation to determine if these findings are valid, understand how ginkgo biloba works on brain cells, and identify an effective dosage and potential side effects.
The National Institute on Aging (NIA) and the Office of Alternative Medicine, both at the National Institutes of Health, are funding a small study to test the effectiveness of ginkgo biloba in treating Alzheimer's Disease. This 2-year study at the Oregon Health Sciences University in Portland started in 1997. It will include 42 patients with mild to moderate Alzheimer's Disease.