Quercetin, a dietary antioxidant flavonoid, has anticarcinogenic prope
rties. We quantified the absorption of quercetin in ileostomists. Abso
rption was 52 +/- 5% for quercetin glucosides from onions, 17 +/- 15%
for quercetin rutinoside, and 24 +/- 9% for quercetin aglycone. The pl
asma quercetin concentration in subjects with an intact colon, after i
ngestion of fried onions, apples and pure quercetin rutinoside, decrea
sed slowly with elimination half-lives of about 25 h. Thus, repeated d
ietary intake of quercetin will lead to accumulation in plasma. The re
lative bioavailability of quercetin from apples and rutinoside was one
-third of that from onions. Absorption kinetics and bioavailibility mi
ght be determined by the type of glycoside. Dietary quercetin could in
crease the antioxidant capacity of blood plasma. (C) 1997 Elsevier Sci
ence Ireland Ltd.