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RE: Study Examines
Corosolic Acid's Effects
on Plasma Glucose Levels
Fukushima M, Matsuyama
F, Ueda N, et al. Effect
of corosolic acid on
postchallenge plasma
glucose
levels. Diabetes Res
Clin Pract. August
2006;73(2):174-177.
The main component of
the leaf extract of
Queens Crape-Myrtle
(Lagerstroemia speciosa)
is a
polyphenol with blood
glucose lowering
effects. However, this
polyphenol does not
account for the
entire blood glucose
lowering activity of the
whole extract. Corosolic
acid is also extracted
from
Queens Crape-Myrtle. It
is unknown whether
corosolic acid has blood
glucose lowering
activity in
humans. The purpose of
this study was to test
corosolic acid in
humans.
Volunteers in Japan (n =
31) with fasting plasma
glucose levels between
110 and 140 mg/dl were
enrolled in this
double-blind,
placebo-controlled,
crossover study.
Subjects who had
hypertension,
hepatic or renal
disease, engaged in
heavy exercise, or took
any medication were
excluded. Nineteen
subjects had diabetes.
Subjects fasted
overnight and then
received 10 mg corosolic
acid or placebo 5
minutes before a 75 g
oral glucose tolerance
test. There was a 7-day
washout period and then
the
participants were
crossed over to the
opposite treatment.
Plasma glucose and serum
insulin levels
were measured for 180
minutes.
There were no
significant differences
in plasma glucose levels
before and 30 min after
treatment.
Corosolic acid produced
lower glucose levels
from 60 to 120 min but
only reached statistical
significance at 90 min
(P < 0.05). At 30 min,
serum insulin levels
were significantly
higher in
corosolic acid-treated
subjects than
placebo-treated subjects
(P-value not indicated).
The mechanism of action
is unknown. The higher
insulin at 30 min may
explain the lower
glucose
levels at 90 min. The
authors conclude that
corosolic acid has a
lowering effect on
postchallenge
plasma glucose levels in
humans. The authors do
not discuss whether the
lowering effect was
clinically relevant. The
graph of the data shows
a small effect.
—Heather S. Oliff, PhD
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