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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

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[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.]

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