Increase In Antioxidants, Decrease In Free Radicals Identified As Likely New Mechanism Of Action For Purple Grape Juice Benefits

"We have already seen that drinking purple grape juice has potentially beneficial effects. This study gives us a better understanding of the mechanisms behind those effects," explains Jane E. Freedman, M.D., assistant professor of medicine and pharmacology at Georgetown University and the lead author of the study. "What we are seeing for the first time is that the flavonoids in purple grape juice work in two related pathways: First, they have a protective effect on antioxidants, allowing them to provide active protection against oxidative stress for longer periods. Second, they also seem to have a direct, positive effect on a number of biological functions like platelet activity, nitric oxide production, and signaling in cells, all of which may be protective factors."

In the study, 20 subjects drank about two cups of juice a day for 14 days (the actual dose was based on body weight; therefore the average female subject consumed less juice). Afterwards, the level of vitamin E (alpha-tocopherol) in their plasma was approximately 13% higher than at the start of the study, the total antioxidant capacity of their plasma increased by 50%, nitric oxide production from platelets increased by 70%, and platelet activity significantly decreased.

Conversely, the study also found that production of superoxide-a potentially harmful free radical-was reduced by a third after supplementation with grape juice. These results were consistent with the initial in vitro test results performed on blood samples drawn from the healthy subjects.

"The 'antioxidant protective' effect we see with the grape juice is new information that, when added to what we already knew about grape juice's other benefits, helps us better understand the mechanisms by which grape juice works in the body," notes Freedman. Healthy production of nitric oxide combats atherosclerosis in several ways. The researchers felt that the higher levels of antioxidants may help preserve the nitric oxide in the body, extending its beneficial effects.

"It's likely that the protective effects of the purple grape juice are due to the juice's flavonoids," Freedman adds. "But interestingly enough, the study found that when individual groups of flavonoids were separated from the juice and tested in isolation, not all of them had the same effect as that of whole juice."

The study, which was primarily funded by the National Institutes of Health (National Heart, Lung and Blood Institute), and also by an unrestricted grant from Welch Foods, Inc., was published in the June 12th issue of Circulation, the official journal of the American Heart Association.