Bioavailabilities of Quercetin-3-Glucoside and Quercetin-4′-Glucoside Do Not Differ in Humans

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Abstract
The flavonoid quercetin is an antioxidant which occurs in foods mainly as glycosides. The sugar moiety in quercetin glycosides affects their bioavailability in humans. Quercetin-3-rutinoside is an important form of quercetin in foods, but its bioavailability in humans is only 20% of that of quercetin-4′-glucoside. Quercetin-3-rutinoside can be transformed into quercetin-3-glucoside by splitting off a rhamnose molecule. We studied whether this 3-glucoside has the same high bioavailability as the quercetin-4′-glucoside. To that end we fed five healthy men and four healthy women (19–57 y) a single dose of 325 μmol of pure quercetin-3-glucoside and a single dose of 331 μmol of pure quercetin-4′-glucoside and followed the plasma quercetin concentrations. The bioavailability was the same for both quercetin glucosides. The mean peak plasma concentration of quercetin was 5.0 ± 1.0 μmol/L (±se) after subjects had ingested quercetin-3-glucoside and 4.5 ± 0.7 μmol/L after quercetin-4′-glucoside consumption. Peak concentration was reached 37 ± 12 min after ingestion of quercetin-3-glucoside and 27 ± 5 min after quercetin-4′-glucoside. Half-life of elimination of quercetin from blood was 18.5 ± 0.8 h after ingestion of quercetin-3-glucoside and 17.7 ± 0.9 h after quercetin-4′-glucoside. We conclude that quercetin glucosides are rapidly absorbed in humans, irrespective of the position of the glucose moiety. Conversion of quercetin glycosides into glucosides is a promising strategy to enhance bioavailability of quercetin from foods.