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First Clinical Study on Purple Grape Juice
In the first clinical study of its kind, researchers from the
University of Wisconsin-Madison found that purple grape juice
(Vitis labrusca L., Vitaceae) helps protect heart health
in those affected by coronary artery disease (Stein et al.,
1999). According to the study, two weeks of grape juice therapy
increased vasodilation (relaxed blood vessels) while decreasing
harmful oxidation of LDL cholesterol. Impaired vasodilation is
thought to be one of the earliest manifestations of heart disease.
Previous clinical studies on red wine have produced similar outcomes,
leading some researchers to speculate that the alcohol content
is the factor that protects against heart disease. The results
of the current study provide support for the theory that flavonoids
(including quercetin, catechins, myricetin, kaempferol) and tannic
acid are the more important constituents in purple grape juice
and red wine. It is also likely that white grape juice and white
wine provide fewer benefits because they contain mainly juice,
without the healthful components from the grape seeds and skins.
In this small study, 15 volunteers (12 men and three women) with
an average age of 63 years consumed approximately 21 ounces of
purple grape juice each day for two weeks. Ten participants had
a history of high blood pressure or were taking antihypertensive
medication, and 11 people had high cholesterol levels or were
receiving cholesterol-lowering treatment. In addition, most of
the participants had been taking vitamins E and C, antioxidant
therapies that may also have an effect on heart health. People
with unstable angina, uncontrolled diabetes mellitus, or recent
medication changes were not allowed to participate in the study.
During the 14-day treatment period, volunteers were instructed
to exclude fruit products, tea (i.e., Camellia sinensis),
and alcoholic beverages from their diet, keeping a daily food
log to assure compliance. Participants served as their own controls,
through a comparison of baseline values and those obtained after
grape juice therapy. The study was single-blinded, meaning that
the practitioners who performed testing had no information about
the patients or the study.
The researchers were particularly impressed with the results
of the study in light of the fact that many volunteers were already
taking heart medications and antioxidant vitamins. During the
course of the study, some participants experienced a small increase
in total cholesterol and triglyceride levels due to the carbohydrate
content of the grape juice. They concluded that the juice therapy
was beneficial in spite of this slight rise in cholesterol levels,
providing "further evidence of the potential usefulness of
purple grape juice."
Although the sample size of 15 people was small, the Madison
research team pointed out that "the BA [high resolution brachial
artery ultrasonography] technique for evaluating endothelial function
[the health of the cells lining the blood vessels] is very sensitive
and reproducible." In addition, researchers used permutation
tests to verify that the observed changes in heart health were,
in fact, related to consumption of grape juice. Because the study
was limited to two weeks, future research should test the effects
of long-term grape juice consumption on heart health. -
Krista Morien, HRF
[Stein JH, Keevil JG, Wiebe
DA, et al. Purple grape juice improves endothelial function
and reduces the susceptibility of LDL cholesterol to oxidation in
patients with coronary artery disease. Circulation 1999;
100: 1050-1055.] |
