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Researchers Complete Ginkgo Review

A recent review of the scientific literature on ginkgo leaf (Ginkgo biloba L., Ginkgoaceae), one of the best researched herbs, yielded evidence in favor of the plant's clinical use in dementia (Ernst and Pittler, 1999). In compiling their review, the research team used the most stringent inclusion criteria, selecting only clinical studies that were randomized, double-blind, and placebo-controlled. Although the authors had initially planned to perform a meta-analysis, data from the studies proved to be too heterogeneous for statistical pooling.

Out of nine studies that met inclusion criteria, the 1997 American study published in the Journal of the American Medical Association (LeBars et al., 1997) was the most impressive. The trial included a large sample size of 327 patients, although only 137 completed the study. It also employed a relatively long treatment period of one year, exceeding the duration of treatment utilized in many pharmaceutical drug studies on dementia. Overall, Alzheimer's disease patients seemed to benefit more from ginkgo therapy than did those with multi-infarct dementia, a decline in brain function caused by multiple strokes. Researchers found no difference in effectiveness based on age or severity of symptoms at baseline. However, on the global rating of clinical symptoms, the clinicians were unable to detect significant differences between ginkgo and placebo. A six-month study of 156 participants supported the results of the JAMA study (Kanowski et al, 1996). The current review also included seven studies ranging in length from four to 12 weeks, most of which demonstrated ginkgo's superiority to placebo.

Although encouraging, the review also revealed many limitations and methodological flaws. Only four studies out of nine scored the maximum five points on the Jadad scale, which assesses methodological quality. In the other five studies, inclusion and exclusion criteria varied widely, creating the possibility that participants without dementia-related conditions may have been included. Similarly, the earlier studies were conducted before consistent outcome measures for dementia were available, making it difficult to compare study results. Although all of the trials were randomized, few authors provided precise details on the randomization procedure they used. In terms of dosage, the amount of ginkgo taken in the active therapy groups ranged from 120 mg to 240 mg daily, and none of the studies attempted to define an optimal treatment regimen. Because ginkgo manufacturers sponsored the research, there is also a possibility of a bias towards publishing positive findings and ignoring negative ones. (This potential problem of publication bias applies to conventional drug research as well.) Finally, the authors pointed out that many of the studies were too short in duration to "yield ultimately compelling results." Likewise, the research showed that ginkgo improved symptoms of dementia, but there is no solid evidence confirming its role in actually delaying clinical deterioration.

Although "none of the current studies is flawless and ultimately convincing," Ernst and Pittler concluded that there is compelling evidence in favor of ginkgo's use in dementia. In addition, there is a body of 40 controlled studies on cerebral vascular insufficiency that indirectly supports ginkgo's use in dementia. Although not well defined, vascular insufficiency shares some of the same symptoms as dementia, such as impaired memory and poor concentration. According to research, the incidence of side effects with ginkgo was not measurably different than with placebo. A large postmarketing surveillance study involving 10,815 people demonstrated mild side effects in just 1.7 percent of participants. Nevertheless, future research is needed "to establish the clinical value of ginkgo for dementia and to answer the multitude of open questions which remain." - Krista Morien, HRF

Full article $20 - Review Order

[Ernst E, Pittler MH. Ginkgo biloba for dementia: a systematic review of double-blind, placebo-controlled trials. Clinical Drug Investigations 1999; 17(4): 301-308.

Full article $20 - Review Order

Kanowski S, Herrmann WM, Stephan K, Wierich W, Hörr R. Proof of efficacy of the Ginkgo biloba extract Egb 761 in outpatients suffering from mild to moderate primary degenerative demetia of the Alzheimer type or multi-infarct demetia. Phytomedicine 1997; 4(1): 3-13.

Full article $20 - Review Order

Le Bars PL, Katz MM, Berman N, Itil TM, Freedman AM, Schatzberg AF. A placebo-controlled, double-blind, randomized trial of an extract of Ginkgo biloba for dementia. JAMA 1997; 278: 1327-1332.]

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