|
Researchers
Claim Ginseng Lacks "Compelling Evidence"
After reviewing existing clinical research
on ginseng, British researchers concluded, ".there is compelling
evidence for none of the claimed indications" (Vogler et al.,
1999). The authors made this claim despite the fact that nine
of the 16 papers reviewed reported a significantly positive effect.
They reportedly weighed these positive results against contradictory
findings in other studies, and also cited small study populations
and the shortage of rigorously controlled and randomized trials
for ginseng as reasons for their conclusion. On the other hand,
it might be argued that the studies combined in this paper are
too diverse to allow for meaningful conclusions.
Scientific literature for the review was
culled from randomized, controlled clinical trials utilizing any
species of ginseng for any indication. Species studied included
Korean [Panax ginseng C.A. Meyer, Araliaceae]; Japanese
[P. japonicus C.A. Meyer]; American [P. quinquefolius
L.]; sanchi [P. notoginseng (Burk.) F.H. Chen.]; Vietnamese
[P. vietnamensis Ha et Grushv.]; and eleuthero, a.k.a.
Siberian ginseng [Eleutherococcus senticosus (Rupr. ex
Maxim.) Maxim, Araliaceae]. Published and unpublished research
in any language was considered. Only double-blind trials using
single-ingredient root extract preparations were included. Sixteen
studies utilizing P. ginseng, P. quinquefolius, or E.
senticosus met the specified criteria and were reviewed.
The reviewers chose to lump different species
of Panax and even Eleutherococcus together in their
review, as if the plants' popular nomenclature carried more weight
than their individual characteristics. They were clearly aware
of the dissimilarities between Panax and Eleutherococcus,
stating, ".their respective active constituents are different."
The reviewed studies utilized a wide range of different standardized
and unstandardized extracts of different ginseng species at various
dosages.
Although the quality of each study was
quantified using the Jadad scale (which evaluates trial methodology
such as randomization, double-blinding, and other criteria), all
seem to have been given comparable weight in the analysis, regardless
of design, methodology, population size, extract used, treatment
dose, or duration of treatment. A positive result for ginseng
was reported in five of the six studies to which the authors assigned
a Jadad score of 4. (Five is the highest possible Jadad score,
which none of these studies achieved.) Studies that reported no
significant effect were also the ones with the smallest ginseng
treatment groups (generally eight to 10 participants). In every
one of the larger studies (24 or more participants receiving any
dose of ginseng), a positive effect was reported.
Seven of the 16 trials reviewed evaluated
the effect of 200 to 400 mg/day P. ginseng extract or 618
to 1235 mg/day P. quinquefolius extract or 3.4 ml/day E.
senticosus extract on physical performance in young, healthy
volunteers. The studies were one to nine weeks in duration, and
study groups consisted of nine to 14 participants per treatment.
Three trials noted a significant ginseng effect during exercise
(e.g., increased oxygen absorption, decreased heart rate, decreased
levels of lactate in the blood) or after completing an exercise
program (e.g., decreased body fat and resting heart rate, and
increased muscle strength and maximal oxygen uptake). The four
trials that reported no effect assessed similar, but not identical,
outcome measures. Four of the seven trials also investigated ginseng's
ability to increase tolerance to exercise-induced stress ("perceived
exertion"), with no significant effect reported.
Of four studies that assessed cognitive
function in young, healthy volunteers and one in elderly volunteers,
three concluded that P. ginseng or E. senticosus significantly
improved performance on tests of mental arithmetic, abstract thinking,
inverted counting, association, or selective memory. The authors
state, "Ginseng may have beneficial effects on psychomotor performance
and cognitive behaviour." Two studies that investigated ginseng's
ability to enhance immune function in healthy volunteers yielded
contradictory findings - but again, different outcome measures
were used. In one placebo-controlled study, there was a significantly
greater increase in the number and activity of leukocytes (white
blood cells) in people who took ginseng. A second, smaller trial
detected no difference between treatment groups.
Positive effects were also reported in
the final two of the 16 trials reviewed. In volunteers with type
II diabetes mellitus, treatment with 200 mg/day ginseng (presumably
P. ginseng) for eight weeks significantly improved participants'
mood, vigor, psychophysical activity, and fasting blood glucose
levels. A study of 93 people with herpes showed that after six
months' treatment with an E. senticosus preparation, 75
percent of volunteers in the ginseng group reported improvement
in the frequency, severity, and duration of their symptoms, compared
with 34 percent in the placebo group. The reviewers devote a number
of paragraphs to market data on ginseng, expressing concern that
marketers make such a wide variety of claims for the herb. They
conclude, "The widespread use of ginseng as a herbal remedy warrants
more rigorous investigations to assess its efficacy and safety."
- Nancy Hoegler, Herb Research Foundation
[Vogler BK, Pittler MH, Ernst E. The efficacy of ginseng: a systematic
review of randomised clinical trials. European Journal of Clinical
Pharmacology 1999; 55: 567-575.]
|
