Purple Grape Juice May Fight Narrowing of the Arteries
Researchers from the University of Wisconsin Medical School have identified ways in which drinking purple grape juice may fight atherosclerosis, or narrowing of the arteries, according to a study in the September 7th issue of Circulation, a journal published by the American Heart Association. The study showed that when fifteen subjects, all people with coronary artery disease, drank purple grape juice for two weeks, the elasticity of their blood vessels significantly increased and the rate at which their LDL cholesterol oxidized significantly decreased.
"This is of great interest," notes John Folts, Ph.D., "because it suggests that consuming purple grape juice could positively effect the atherosclerotic process in several important ways. Previously, much of the potential benefit of consuming purple grape juice was attributed to its apparent ability to make the blood less likely to clot. Now we see that there appear to be two other beneficial factors at work as well."
Dr. Folts, the senior author of the study and director of the Coronary Thrombosis Research and Prevention Laboratory at the University of Wisconsin Medical School, has conducted extensive research in this area, with much of his previous work focusing on the ability of grape products to reduce the stickiness of blood platelets.
"There are a number of primary contributors to atherosclerosis," explains Folts, "Three of them are the stickiness of our blood, the reduced flexibility of our arteries, and the speed at which we oxidize LDL cholesterol. In previous studies, we saw that drinking purple grape juice reduced blood stickiness. What this study suggests is that drinking the juice has a beneficial effect on two other primary contributors as well."
Vasodilation
The ability of the blood vessels to expand in response to increased blood flow and thus deliver more oxygen where it's needed is called flow-mediated vasodilation. It is indicative of the health of the endothelium - the layer of cells which lines the interior wall of all the blood vessels in the body. When the endothelium is impaired, such as in people with existing coronary artery disease, blood vessels are less able to respond to the sudden need for increased blood flow. They are also more susceptible to atherosclerosis, or narrowing of the arteries, and blood clot formation.
When blood clots in a narrowed artery, a heart attack or stroke may occur. The study looked at fifteen men and women (average age 62.5 ± 12.7) with coronary artery disease. Each person drank approximately 7 cc/kg/day of the juice for 14 days. Flow mediated vasodilation - the ability of the arteries to expand in response to increased flow of blood - was measured at baseline as 2.2mm ± 2.9%. After the juice was consumed for 14 days, flow mediated dilation was measured again and found to be 6.4mm ± 4.7% (p= 0.003), resulting in a mean change of 4.2mm ± 2.9% (p<0.001) - almost triple the previous ability of the blood vessels to respond to increased blood flow.
LDL Oxidation Rates
In studying LDL oxidation, blood samples were drawn and LDL oxidation lag time was measured for each subject at the beginning of the study and then again at its conclusion. Lag time measurement is a commonly used method for determining how long it takes for cholesterol to oxidize when exposed to certain oxidant chemicals. The longer the lag time, the slower the onset of LDL oxidation. The slower the onset of oxidation, the less likely that oxidation will contribute to atherosclerosis, since oxidized cholesterol contributes to the build-up of plaque in the arteries.
Among the entire group, the lag time improved by 34.5% (p= 0.015). At the beginning of the study the average lag time was 87 minutes (± 29 minutes). After the juice was consumed for 14 days, lag time was measured again. After the juice, average lag time improved to 117 minutes (± 23 minutes). Eleven patients in the study were consuming vitamin E (400IU/day). For them, the initial lag time was 86 minutes (± 33 minutes); after drinking the juice it improved to 121 minutes (± 24 minutes).
"People with excellent cardiovascular health usually have healthy endothelial function, a slow onset of LDL oxidation and moderate blood platelet activity," notes Folts. "This study suggests that drinking purple grape juice may promote these heart healthy mechanisms. Combined with what we have learned from previous studies on grape juice's ability to decrease platelet activity, it makes sense to include daily consumption of purple grape juice as part of a diet high in fruits and vegetables and low in saturated fat."
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Note to Editor: Complete study citation: Stein JH, Keevil JG, Aeschlimann S, Folts JD, Purple grape juice improves endothelial function and reduces the susceptibility of LDL cholesterol in patients with coronary artery disease. Circulation, September 7, 1999