Quercetin lowers plasma uric acid in pre-hyperuricaemic males: a randomised, double-blinded, placebo-controlled, cross-over trial
Reviewer: Dr. Alan Gaby, MD
Author: Shi Y, Williamson G
Reference: Quercetin lowers plasma uric acid in pre-hyperuricaemic males: a randomised, double-blinded, placebo-controlled, cross-over trial. Br J Nutr 2016;115:800-806.
Design: Randomized, double-blind, placebo-controlled crossover trial.
Participants: Twenty-two healthy males (aged 19-60 years) with a plasma uric acid level in the high-normal range.
Study Medication and Dosage: 500 mg of quercetin or placebo once a day for 4 weeks. After a 4-week washout period, each person received the alternate treatment for an additional 4 weeks.
Primary Outcome Measure: Change in plasma uric acid levels.
Key Findings: After 4 weeks, compared with baseline, the mean plasma uric acid level fell by 7.9% in the quercetin group (p < 0.01) and increased by 1.6% in the placebo group.
Practice Implications: An elevated uric acid level is a risk factor for gout and for cardiovascular disease. Xanthine oxidase is an enzyme that plays a role in the biosynthesis of uric acid. Quercetin has been found to inhibit bovine xanthine oxidase in vitro, with an apparent Km of 3.2 µmol/L. That concentration is only about twice as high as the plasma quercetin concentration attained when healthy volunteers ingested 220 g per day of onions (providing 114 mg per day of quercetin) for 7 days. Thus, the dosage of quercetin used in the present study (500 mg per day) might produce a plasma quercetin concentration high enough to decrease uric acid production. Although the decrease in plasma uric acid levels observed in this study was only modest, quercetin supplementation could be a useful adjunct to dietary modifications for people with elevated uric acid levels. The possibility that a larger dose of quercetin would have a greater effect warrants investigation.
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