Effect of fruit juice intake on urinary quercetin excretion and biomarkersof antioxidative status

Background: Epidemiologic studies suggest that foods rich in flavonoids mig ht reduce the risk of cardiovascular disease. Objective: Our objective was to investigate the effect of intake of flavono id-containing black currant and apple juice on urinary excretion of quercet in and on markers of oxidative status. Design: This was a crossover study with 3 doses of juice (750, 1000, and 15 00 mL) consumed for 1 wk by 4 women and 1 man corresponding to an intake of 4.8, 6.4, and 9.6 mg quercetin/d. Results: Urinary excretion of quercetin increased significantly with dose a nd with time. The fraction excreted in urine was 0.29-0.47%. Plasma quercet in did not change with juice inter vention, Plasma ascorbate increased duri ng intervention because of the ascorbate in the juice. Total plasma malondi aldehyde decreased with time during the 1500-mL juice intervention, indicat ing reduced lipid oxidation in plasma. Plasma 2-amino-adipic semialdehyde r esidues increased with time and dose, indicating a prooxidant effect of the juice, whereas erythrocyte 2-aminoadipic semialdehyde and gamma-glutamyl s emialdehyde concentrations, Trolox-equivalent antioxidant capacity, and fer ric reducing ability of plasma did not change. Glutathione peroxidase activ ity increased significantly with juice dose. Conclusions: Urinary excretion of quercetin seemed to be a small but consta nt function of quercetin intake. Short-term, high intake of black currant a nd apple juices had a prooxidant effect on plasma proteins and increased gl utathione peroxidase activity, whereas lipid oxidation in plasma seemed to decrease. These effects might be related to several components of the juice and cannot be attributed solely to its quercetin content.