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- Ginkgo (Ginkgo biloba)
- Cognition
- Meta-analysis
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Date:
01-15-2013 | HC# 111256-464
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Re: Meta-analysis Determines Clinical Trials of Ginkgo Extract in Healthy Adults Show Little Effect for Cognitive Enhancement
Laws
KR, Sweetnam H, Kondel TK. Is Ginkgo
biloba a cognitive enhancer in healthy individuals? A meta-analysis. Hum Psychopharmacol. 2012;27(6):527-533.
Ginkgo
(Ginkgo biloba) leaf standardized
extract is used to improve memory and learning. Meta-analyses evaluating ginkgo
in people with Alzheimer's disease or schizophrenia have been published.
According to the authors, there are no meta-analyses in healthy individuals; only
qualitative reviews with varying conclusions. [Note: However, a systematic
review of 16 clinical trials in normal, healthy adults taking ginkgo extract
was published in the American Botanical Council's peer-reviewed journal, HerbalGram, in 2005 and 13 of these trials showed positive conclusions for
memory enhancement, speed of processing abilities, time for mental functions,
etc.1] Hence, the purpose of this study was to conduct a
meta-analysis of the cognitive-enhancing properties of ginkgo in healthy
individuals.
Scopus,
Medline, and Google Scholar were searched from inception through March 2012 with
the keywords Ginkgo biloba, cogniti*,
and neuropsych*. Included studies measured memory, executive function, or
attention in humans; had a double-blind, randomized, controlled design; explained
the dosing regimen and testing structure; and presented appropriate data to
derive effect scores. Only chronic effects were included in the meta-analysis. The
extract/formulation of the ginkgo used in each study was recorded but was not a
defining criterion.
Data
from the included clinical trials were subjected to various statistical
computations and a meta-analysis was conducted on the extracted data.
A
total of 1121 studies that met the search criteria were identified, and 10 clinical
trials containing 13 datasets were used in the analysis. In the analysis of
memory, executive function, and attention, the weighted mean effect size was
close to 0, and the differences between the ginkgo and control groups were not
significant. There was no evidence of publication bias. Effect size was not
significantly related to age, time period of the trial, daily dose, total dose
over the course of the trial, total sample size, or ginkgo formulation. Two of
the most clinically tested brands of ginkgo extract were used in most of the
studies: EGb 761® (Dr. Willmar Schwabe GmbH & Co. KG; Karlsruhe,
Germany) and LI 1370 (Lichtwer Pharma AG; Berlin, Germany).
The
authors conclude that ginkgo has no significant impact on memory, executive
function, or attention in healthy subjects. The authors point out that meta-analyses
increase the power to detect small differences, even when the individual study
sample sizes are small or if they contain nonsignificant findings. Studies with
a small sample size may be underpowered to detect statistical differences, and
nonsignificant findings may result. Combining all of the data into a
meta-analysis is like having a huge study that is adequately powered to detect
small or large statistical differences between treatments. If a meta-analysis
were conducted properly (i.e., the combined data need to be from studies of a similar
design), then the conclusions would be considered authoritative. This study was
statistically robust; however, the authors combined data from 4 different
ginkgo formulations, 4 different doses, and 6 different treatment durations, so
the conclusions are not authoritative. Unfortunately, there are not enough studies
that have a similar design to do an authoritative meta-analysis.
—Heather S. Oliff,
PhD
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