A vast body of research supports numerous health benefits for
ginkgo extracts, particularly for treating various symptoms and conditions
associated with declining cognitive performance and poor circulation, says the
American Botanical Council, an independent nonprofit research and education
organization.
A new six-year clinical trial
will be published Wednesday, November 19, in the Journal of the American
Medical Association.1 In the Ginkgo Evaluation of Memory (GEM)
trial, a leading ginkgo extract was not effective
in preventing the development of dementia in older adults. The ginkgo
failed to reduce the overall incidence rate of dementia in a total of 3069
elderly individuals (minimum 75 years; average age 79) with normal cognition or
those with mild cognitive impairment (MCI).
Researchers used the world’s
most tested ginkgo extract (EGb 761®; made by W. Schwabe of Karlsruhe, Germany).
The dosage used by 1545 subjects was 240 mg per day (120 mg twice daily) of the
ginkgo tablets or a matching placebo (for 1524 people). Described as a randomized,
double-blind, placebo-controlled trial conducted from 2000 to 2008,1,2
Steven T. DeKosky, M.D., currently dean of the University of Virginia School of
Medicine (at the University of Pittsburgh, PA during the time of the study) and
colleagues evaluated 2587 cognitively intact adults plus 482 adults with MCI.
They were assessed every 6 months for dementia in 5 academic centers for 6.1
years.
The authors acknowledge that
one of possible shortcomings of this trial is “because
the delay from initial brain changes to clinical dementia is known to be long,
it is possible that an effect of G. biloba, positive or negative, may
take many more years to manifest.”1
In an accompanying editorial,
Lon S. Schneider MD of the University
of Southern California, Los Angeles, “Despite 2
decades of research with standardized extracts of Ginkgo biloba,
considerable uncertainty about its pharmacology and clinical effects remains.”3
ABC’s Response to the GEM
trial
“There is a significant body
of scientific and clinical evidence supporting the safety and efficacy of
ginkgo extract for both cognitive function and improved circulation,” said Mark
Blumenthal, the founder and executive director of ABC.
In addition to the issue of a
longer duration raised by the authors, ABC noted that another potential
weakness of this trial is the lack of an active control, i.e., a potential
third arm of the trial in which patients would have used a pharmaceutical
medication with known efficacy, to determine to what extent the particular
population being tested would respond. This was not possible for this trial
since no conventional pharmaceutical drug has ever demonstrated the ability to
prevent the onset of dementia or diminish its progression.
Further, the trial notes that
only about 60% of the patients were in compliance with their use of the ginkgo
or placebo by the end of the trial. It is unclear whether the poor adherence to
the assigned treatment might have had a negative effect on the trial’s results.
According to ABC’s
Blumenthal, “Ginkgo’s benefits must be viewed in the context of the entirety of
the published clinical data,” – a reference to numerous controlled clinical
trials that support the use of ginkgo extract for treating symptoms of MCI and
even early stage Alzheimer’s disease, as well as the circulatory benefit of
increasing the ability of older people to walk distances with less leg pain (a
condition known as peripheral arterial occlusive disease or intermittent
claudication).
Veteran Maryland psychopharmacologist Jerry Cott,
PhD, a member of the ABC Advisory Board, stated in an e-mail to CNN that due to
the extreme difficulty and expense in generating useful life-style type
clinical research data he often places more value in the basic science, i.e.,
“the pharmacology, rather than controlled clinical trials. The science for
ginkgo says that it has physiological and biochemical effects in human and
animal tissues that would surely be beneficial for many chronic illnesses,
especially those that have a vascular component.”4
ABC also emphasized that the
GEM trial is only 1 of about 5 clinical trials that are being conducted to try
to determine if ginkgo extract can have a preventive effect on elderly adults
and lessen the potential progression to dementia. Another large trial is
currently underway with the results not expected for at least one year.5
ABC emphasized that ginkgo
extract has been shown to be effective in treating symptoms of dementia
in numerous controlled clinical trials as well as in population-based
(epidemiological) studies. For example, 2 epidemiological studies conducted in France
(known as the EPIDOS & PAQUID studies) have demonstrated a positive effect
of the Schwabe EGb 761® ginkgo extract on the onset of Alzheimer’s dementia6
and the length of patients’ survival.7 These trials suggest that
this ginkgo extract may be beneficial and appropriate therapy for elderly
adults.
Further, an NIH sponsored
study in the United States
in 2008 demonstrated a beneficial effect of a standardized ginkgo extract on
the risk of developing dementia in only the trial subjects taking the ginkgo on
a regular basis.8
In addition to being tested
for cognitive impairment, at least 16 controlled clinical trials have
demonstrated benefits of various ginkgo extracts for healthy, non-cognitively
impaired adults. A comprehensive review has shown that in 11 of these trials,
the ginkgo increased short-term memory, concentration and time to process
mental tasks.9
ABC also noted that ginkgo
extract has been shown to be effective in controlled clinical for treating
patients with peripheral arterial occlusive disease (PAOD), a condition in
older people characterized by pain in the legs while walking due to inadequate
circulation. A systematic review of 9 controlled clinical trials found that in
at least 7 trials the ginkgo extract exhibited safe and effective benefits
compared to placebo.10
About Ginkgo Extract
Ginkgo (Ginkgo biloba)
is the world’s oldest living tree, dating back about 250 million years. Ginkgo
leaves have been used in traditional Chinese medicine for about 500 years. For
about the past 30 years the leaves of ginkgo have been made into a highly
concentrated (50:1) extract, chemically standardized to compounds unique to
ginkgo (ginkgolides and bilobalide) as well as other compounds. The leading
German ginkgo extract has been subjected to a vast range of clinical trials
documenting its ability to improve peripheral circulation and cognitive
function, particularly in patients with early stages of mild cognitive
impairment, senile dementia, Alzheimer’s disease, and memory loss. Clinical
trials also support the use of ginkgo extract in assisting elderly patients in
walking longer distances without leg pain (PAOD, also known as intermittent
claudication). Standardized ginkgo extracts are approved for use as medicines
in Germany
and numerous other countries.
References
1. DeKosky ST, Williamson J,
Fitzpatrick A, Kronmal RA, Ives DG, Saxton J, Lopez O, Burke G, Carlson M,
Fried L, Kuller LH, Robbins J, Tracy RP, Woolard NF, Dunn L, Snitz BE, Nahin
RL, Furberg CD for the GEM Study Investigators. Ginkgo biloba for primary prevention
of dementia: Results of the Ginkgo Evaluation of Memory (GEM) Study. JAMA
Nov 19, 2008;300(19):2253-2262.
2. American Medical
Association. Ginkgo biloba does not appear to prevent dementia, Alzheimer’s
disease [press release]. Chicago,
IL: Nov. 13, 2008.
3. Schneider L. Ginkgo biloba
extract and preventing Alzheimer’s disease. JAMA Nov 19, 2008;
300(19):2306-2308.
4. Cott J e-mail to Elizabeth
Cohen (CNN), Nov. 16, 2008
5. Andrieu S, Ousset PJ,
Coley N, Ouzid M, Mathiex-Fortunet H, Vellas B, GuidAge Study Group. GuidAge
study: a 5-year double-blind, randomized trial of EGb 761 for the prevention of
Alzheimer’s disease in elderly subjects with memory complaints. I Rationale,
Design and baseline data. Curr Alz Res 2008;5:406-415.
6. Andrieu S, Gillette S,
Amouyal K, Nourhashemi F, Reynish E, Ousset PJ, Albarede JL, Vellas B,
Grandjean H. Association of Alzheimer’s disease onset with Ginkgo biloba and
other symptomatic cognitive treatments in a population of women aged 75 years
and older from the EPIDOS study. J Gerontol Med Sci 2003;58A:372-377.
7. Dartigues JF, Carcaillon
L, Helmer C, Lechevallier N, Lafuma A, Khoshnood B. Vasodilators and Nootropics
as Predictors of Dementia and Mortality in the PAQUID Cohort. J Am Geriatr
Soc 2007; 55:395–399.
8. Dodge HH, Zitzelberger T,
Oken BS, Howieson D, Kaye J. A randomized placebo-controlled trial of Ginkgo
biloba for the prevention of cognitive decline. Neurology 2008;70:1809-1817.
9. Crews W, Harrison DW,
Griggin ML, Falwell KD, Crist T, Longest L, Hehemann L, Rey ST. The neuropsychological efficacy
of ginkgo preparations in healthy and cognitively intact adults; A
comprehensive review. HerbalGram 2005;67:42-62.
10. Horsch S, Walther C. Ginkgo biloba special extract
EGb 761 in the treatment of peripheral arterial occlusive disease (PAOD) – a
review based on randomized, controlled studies. Int J Clin
Pharmacol Ther. 2004 Feb;42(2):63-72. |