RELATIVE BIOAVAILABILITY OF THE ANTIOXIDANT FLAVONOID QUERCETIN FROM VARIOUS FOODS IN MAN

Quercetin is a strong antioxidant and a major dietary flavonoid. Epide miological studies suggest that consumption of quercetin protects agai nst cardiovascular disease, but its absorption in man is controversial . We?ie fed nine subjects a single large dose of onions, which contain glucose conjugates of quercetin, apples, which contain both glucose a nd non-glucose quercetin glycosides, or pure quercetin-3-rutinoside, t he major quercetin glycoside in tea, Plasma levels were then measured over 36 h, Bioavailability of quercetin from apples and of pure querce tin rutinoside was both 30% relative to onions, Peak levels were achie ved less than 0.7 h after ingestion of onions, 2.5 h after apples and 9 h after the rutinoside. Half-lives of elimination were 28 h for onio ns and 23 h for apples. We conclude that conjugation with glucose enha nces absorption from the small gut, Because of the long half-lives of elimination, repeated consumption of quercetin-containing foods will c ause accumulation of quercetin in blood. (C) 1997 Federation of Europe an Biochemical Societies.