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- Ginkgo (Ginkgo biloba)
- Cognition
- Dementia
| Date:
08-15-2011 | HC#
041153-430
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Re: Meta-analysis Shows Ginkgo to Be Effective for Mild Dementia
Wang
B-S, Wang H, Song Y-Y, et al. Effectiveness of standardized Ginkgo biloba extract on cognitive
symptoms of dementia with a six-month treatment: a bivariate random effect
meta-analysis. Pharmacopsychiatry. May 2010;43(3):86-91.
Dementia
is the age-related loss of thinking, reasoning, and remembering skills. There
is currently no cure for dementia. Drugs may be helpful in delaying progression
of the disease and improving some symptoms, but the benefits are modest, and adverse
side effects can be serious. Herbs are being explored as an alternative to drug
treatment for people with dementia. Ginkgo (Ginkgo
biloba) leaf extract is the herb most commonly used to reduce the symptoms
of dementia.
More
than 30 published placebo-controlled trials have evaluated the effectiveness of
ginkgo extract in people with dementia. Some studies found that ginkgo extract
was no better than placebo in reducing cognitive symptoms, while other studies
found ginkgo extract was superior to placebo. In these studies, the difference
between ginkgo and placebo was due to both improvements in the ginkgo-treated
group and natural progression of dementia in the untreated placebo group. Systematic
reviews should take into account the widely variable cognitive decline that
occurs in untreated dementia patients in placebo groups. This variation is
called the baseline risk. Short term studies (< 6 months) are insufficient
to measure effects and may also contribute to mixed results. The purpose of
this article was to review trials with intervention periods of at least 6
months and to conduct a bivariate random effects meta-analysis of the impact of
ginkgo extract in people with dementia, taking into account the influence of baseline
risk.
The
researchers searched PubMed and Cochrane Library databases to identify articles
published in English from January 1980 to January 2009. The researchers also
searched bibliographies of published trials and systematic review articles for
additional trials. Criteria for inclusion were randomized, double-blind,
placebo-controlled trials; diagnosis of dementia by prospective criteria; use
of standardized ginkgo extract in any dose and dosage form; trial duration of
at least 24 weeks, as long as outcomes were reported at 24 ± 2 weeks; clearly
stated exclusion criteria; and use of at least one objective assessment of
cognitive function as an outcome measure. The Alzheimer's Disease Assessment
Scale-cognition (ADAS-cog) and/or the Syndrom Kurz Test scale (SKT) were used
as assessment tools in the trials. In this meta-analysis, SKT scores were
converted to ADAS-cog scores in order to directly compare results.
The
search identified six trials that met all the inclusion criteria. The duration
of the intervention ranged from 22 to 52 weeks, and ginkgo doses ranged from
120 to 240 mg extract daily. The six trials involved a total of 1,838 participants,
with 1,004 receiving ginkgo extract and 834 receiving placebo. Mean ages of the
participants ranged from 64 to 78 years, and the mean proportion of female
participants ranged from 52-72%. The average dementia severity was rated as
mild at baseline, using average cognitive scores.
The
bivariate random effects meta-analysis of data from the six trials showed a significant
difference in ADAS-cog scores between ginkgo and placebo. The estimated
difference of change in scores was -2.65 (95% confidence interval [CI], -4.53
to -0.76), which was a significant difference in favor of ginkgo extract. According
to the authors, this meta-analysis demonstrated that ginkgo extract given for a
period of six months significantly improved cognitive function in people with mild
dementia.
The
authors explain that progression of dementia is influenced by many factors and
the rate of cognitive decline can vary considerably. Variations in baseline
risk can lead to conflicting results in clinical trials of dementia treatments.
Results of this meta-analysis suggest that direct comparisons of numerical
differences between placebo and treatment groups, without taking into account
the baseline risk, is not a reliable way to evaluate the efficacy of ginkgo
extract in people with mild dementia.
The
authors discuss some limitations of this study. Because only six trials met the
inclusion criteria, the amount of data was relatively small. Conversion of SKT
scores to ADAS-cog scores may not have accurately represented participants' actual
ADAS-cog scores. The data came only from published clinical trials in the
scientific literature, thereby creating the possibility of publication bias.
The
authors did not explain why they chose to limit their analysis to clinical
trials published in English. Excluding trials published in other languages reduced
the amount of data available for the meta-analysis. It may also have introduced
bias and limited the applicability of the results. Two high quality trials in
progress at the time of publication will help bring more data to bear in
understanding the benefits of ginkgo in the dementia patient.
—Heather S. Oliff, PhD
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