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
[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.
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.
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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