Consumption of flavonoids in onions and black tea: lack of effect on F-2-isoprostanes and autoantibodies to oxidized LDL in healthy humans

Background: Oxidative damage to lipids in vivo may be involved in the devel opment of atherosclerosis and cancer. Onions and black tea are foods rich i n flavonoids, predominantly the flavonoid quercetin, which is a potent in v itro inhibitor of membrane lipid peroxidation and LDL oxidation. Objective: Our objective was to investigate the effects of consuming a high -flavonoid (HF) diet enriched with onions and black tea on indexes of oxida tive damage in vivo compared with a low-flavonoid (LF) diet. Design: Thirty-two healthy humans were studied in a randomized crossover de sign. Indexes of oxidative damage used were plasma F-2-isoprostanes (a biom arker of Lipid peroxidation in vivo) and the titer of antibodies to malondi aldehyde (MDA)-modified LDL. Results: There were no significant differences in the intake of macronutrie nts or assessed micronutrients, plasma F-2-isoprostane concentrations, and MDA-LDL autoantibody titer between the HF and LF dietary treatments. In the men, however, plasma concentrations of the F-2-isoprostane 8-epi-prostagla ndin F,, were slightly higher after the HF treatment phase than after the L F treatment [0.31 +/- 0.029 nmol/L (111 +/- 10.4 ng/L) compared with 0.26 /- 0.022 nmol/L (92 +/- 7.8 ng/L); P = 0.041]. In all subjects, plasma quer cetin concentrations were significantly higher after the HF treatment phase than after the LF treatment: 221.6 +/- 37.4 nmol/L compared with less than the limit of detection of 66.2 nmol/L. Conclusion: Flavonoid consumption in onions and tea had no significant effe ct on plasma F-2-isoprostane concentrations and MDA-LDL autoantibody titer in this study and thus does not seem to inhibit lipid peroxidation in human s.