Regular Consumption of Concord Grape Juice Benefits Human Immunity

gamma delta T cells are important immune surveillance cells residing in epithelial layers lining the intestine, lung, and reproductive tract. The main objective of this study was to test the hypothesis that consumption of dietary compounds from grapes would modify gamma delta T-cell function. Other factors related to immune function after grape juice consumption were also tested. A randomized, double-blind, placebo-controlled, parallel intervention was conducted: 100% grape juice made from Concord grapes or a placebo beverage was consumed by 85 individuals daily for 9 weeks. Subjects were asked not to consume other red, blue, and purple fruits during the study. Blood samples, taken at the beginning and the end, were analyzed for gamma delta T-cell numbers and proliferation, vitamin C, antioxidant capacity, and the ability to protect DNA from strand breaks. Those consuming the grape juice had significantly greater numbers of circulating gamma delta T cells and higher serum vitamin C levels compared to the placebo by two-way repeated-measure analysis of variance (P < .05). Individuals consuming the placebo had lower serum antioxidant activity, less gamma delta T-cell proliferation, and increased DNA strand breaks when challenged with H2O2. Analysis of the data by structural equation modeling confirmed that 61% of the variance in biological functions at 9 weeks was due to grape juice consumption. Based on conventional statistical analyses, as well as on sophisticated modeling techniques, regular consumption of purple grape juice in the absence of other red, blue, or purple fruits benefited immunity in healthy, middle-aged human subjects.