Objective: To determine the potential antioxidant effect of rutin (quercetin-3-O-b-rutinoside) supplementation. Design: A 6-week randomized single-blind placebo controlled trial was conducted; 500 mg rutin supplement was compared to an equivalent amount of glucose placebo. In addition, a pharmacokinetic study was carried out. Setting: The Rowett Research Institute, Aberdeen, UK. Subjects: Eighteen healthy non-obese normocholesterolaemic female volunteers in the age range 18 ± 48 y. Main outcome measures: Plasma¯avonoids, ascorbic acid, tocopherols and carotenoids, plasma antioxidant capacity, lymphocyte DNA damage, blood chemistry and haematology, liver function tests, urinary malondialdehyde, 8-hydroxy-2H -deoxyguanosine and 8-iso-prostaglandin F 2a . Results: Eighteen volunteers completed the trial. Rutin supplementation did not induce any adverse changes in blood chemistry or indices of liver function. Plasma¯avonoids were signi®cantly elevated in the rutinsupplemented group. Endogenous oxidation of pyrimidines was signi®cantly decreased in both rutin-and placebo-treated volunteers. There was no signi®cant change in the level of urinary 8-hydroxy-2 H -deoxyguanosine or urinary malondialdehyde in either group. A linear correlation was observed between urinary malondialdehyde and urinary 8-iso-prostaglandin F 2a (R 0.54, P`0.01). Conclusion: Six weeks' rutin supplementation signi®cantly elevated the levels of three plasma¯avonoids (quercetin, kaempferol and isorhamnetin) but there was no signi®cant change in plasma antioxidant status. The decrease in the level of endogenous base oxidation in lymphocyte DNA seen in both the placebo-and rutinsupplemented subjects may re¯ect seasonal changes in other dietary antioxidants.

Both meals--onions, and onions together with tomatoes--led to transient decreases in biomarkers of oxidative stress, although the particular biomarkers affected differ. It is possible that the differences in patterns of response reflect the different uptakes of flavonoids but the underlying mechanism is not understood.