ABSORPTION AND DISPOSITION KINETICS OF THE DIETARY ANTIOXIDANT QUERCETIN IN MAN

Quercetin is a dietary antioxidant that prevents oxidation of low-dens ity lipoproteins in vitro by scavenging of free oxygen radicals. Its i ntake was inversely associated with coronary heart disease mortality i n Dutch elderly men. However, data on absorption of quercetin in man a re scarce and contradictory. We studied the time course of the plasma quercetin concentration in two subjects after ingestion of fried onion s containing quercetin glucosides equivalent to 64 mg of quercetin agl ycone. Peak plasma levels of 196 ng/ml were reached after 2.9 h, with a half-life of absorption of 0.87 h. The half-life of the distribution phase was 3.8 h, and of the subsequent elimination phase 16.8 h. Afte r 48 h the plasma concentration was about 10 ng/ml. We conclude that q uercetin glucosides from onions are absorbed and are eliminated slowly throughout the day. Thus, the dietary antioxidant quercetine could in crease the antioxidant capacity of blood plasma.