Comparison of the antioxidant effects of Concord grape juice flavonoids and α-tocopherol on markers of oxidative stress in healthy adults

Background: Concord grape juice (CGJ) is a rich source of flavonoids, which have greater antioxidant efficacy in vitro than does α-tocopherol; however, the efficacies of flavonoids and α-tocopherol in vivo have not been compared. Objective: We compared the in vivo antioxidant efficacy of CGJ with that of α-tocopherol in healthy adults. Design: Subjects were randomly assigned to receive either 400 IU RRR-α-tocopherol/d (n = 17) or 10 mL CGJ · kg^-1 · d^-1 (n = 15) for 2 wk. Serum oxygen radical absorbance capacity, plasma protein carbonyls, urinary F₂-isoprostanes, and resistance of LDL to ex vivo oxidation were measured before and after supplementation as markers of antioxidant status and oxidative stress. Results: After supplementation, plasma α-tocopherol increased 92% in subjects who received α-tocopherol (P < 0.001); plasma total and conjugated phenols increased 17% (P < 0.01) and 22% (P < 0.001), respectively, in subjects who received CGJ. There was a significant change in plasma triacylglycerols in both groups, but the concentrations were within the normal range. CGJ supplementation was associated with significantly higher triacylglycerols than was α-tocopherol supplementation. Both supplementation regimens significantly increased serum oxygen radical absorbance capacity (P < 0.001) and LDL lag time (P < 0.001) and significantly decreased the LDL oxidation rate (P < 0.01), with no significant difference in effectiveness. Protein carbonyl concentrations in native plasma decreased 20% after CGJ supplementation, which was a significantly different response than that after α-tocopherol supplementation (P < 0.05). Conclusions: In healthy adults, 10 mL CGJ · kg^-1 · d^-1 increased serum antioxidant capacity and protected LDL against oxidation to an extent similar to that obtained with 400 IU α-tocopherol/d but decreased native plasma protein oxidation significantly more than did α-tocopherol. CGJ flavonoids are potent antioxidants that may protect against oxidative stress and reduce the risk of free radical damage and chronic diseases.