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First Clinical Study on Black Grape Juice

 

In the first clinical study of this type, researchers at the University of Wisconsin-Madison discovered that black grape juice (Vitis labrusca L., Vitaceae) helps protect the heart's health in affected people of coronary artery disease (Stein et al., 1999). According to the study, two weeks of grape juice therapy increased vaso-dilation (relaxation of blood vessels) while decreasing the harmful oxidation of LDL cholesterol. Altered vasodilation is believed to be one of the first manifestations of heart disease. Previous clinical studies on red wine produced similar results, prompting some researchers to speculate that alcohol content is a protective factor against heart disease. The results of the current study provide support for the theory that flavonoids (such as quercetin, myricetin, and kaempfero) and other polyphenols such as catechins and tannic acid are the most important ingredients in black grape juice and red wine. It is also likely that white grape juice and white wine will bring less benefits because they contain mainly juice, without the health promoting ingredients from the seeds and skin of the black grapes.

In this small study, 15 volunteers (12 men and 3 women) with a mean age of 63 years consumed approximately 21 ounces (595.35 grams) of grape juice a day for two weeks. Ten participants had a history of hypertension or were taking antihypertensive medication, and 11 people had high cholesterol or were being treated for cholesterol reduction.

In addition, most participants had been taking vitamins E and C, antioxidant therapies that could also have their effect on heart health. People with unstable angina pectoris, uncontrolled diabetes mellitus or who had had recent changes in their medication were not allowed to participate in the study. During the 14-day treatment period, volunteers were instructed to exclude from their diet fruit-based products, tea (ie Camellia sinensis (L.) Kuntze, Theaceae) and alcoholic beverages at the same time who maintained a daily food record to ensure compliance with the study requirements. The same participants served as controls through a comparison of the values measured at the beginning of the study and those obtained after therapy with grape juice. The study was simple-blind, which means that the therapists who performed the tests had no information about patients or the study.

The researchers were especially impressed with the results of the study, since many of the 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 grape juice. They concluded that juice therapy was beneficial despite this small increase in cholesterol levels, providing "further evidence of the potential utility of black grape juice."

Although the sample size of 15 people was small, the Madison research team noted that "the EA technique (high-resolution brachial artery ultrasound) for the assessment of endothelial function (the health of cells lining blood vessels) is very sensitive and reproducible." In addition, the researchers used permutation tests to verify that observed changes in heart health were actually related to the consumption of grape juice. Because the study was limited to two weeks, future research should assess the long-term effects of grape juice consumption on heart health.
- Krista Morien, HRF

Source: 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
Extract from the journal Complementary Medicines N ° 62 -AMC-