Background and Objective: High blood uric acid (hyperuricemia) is a common phenomenon in populations with hypertension, hyperglycemia, obesity and/or dyslipidemia. This study was to investigate the effects of quercetin supplementation on blood uric acid level and the biochemical mechanism behind it.
Methods: A pilot trial confirmed the delivery of quercetin from a supplement tablet in healthy males (n=6). Randomised, double-blind, cross-over, placebo-controlled 4-week dietary intervention trial with the same supplement tablet containing 500 mg quercetin d-1 was conducted in selected healthy males (n=22, with higher blood uric acid but within normal range). Changes of uric acid and glucose were analysed in fasting blood plasma at 0, 2 and 4 weeks. Plasma metabolomics were profiled by 1H-NMR. Where quercetin and its metabolites may affect in the pathway of uric acid metabolism was investigated in vitro and ex vivo.
Results: At the end of the 4-week trial, plasma uric acid levels were significantly reduced (mean change -26.5 µM, 95% CI -7.6 to -45.5, P = 0.008, n=22), as were diastolic blood pressures in normotensive subjects (-3.1 mm Hg, -0.5 to -5.8, P = 0.048, n=10). Paired plasma 1H-NMR spectrum showed lowered glutamine (P = 0.008), acetoacetate (P = 0.005) and lactate (P = 0.03) after quercetin treatment. A dose-dependent inhibition of quercetin, quercetin-3'-O-sulfate and 3,4-dihydroxyphenylacetic acid on xanthine oxidase in vitro and a mild inhibitory effect of quercetin on plasma adenosine deaminase was found.
Conclusions: Quercetin supplementation can maintain blood uric acid level and blood pressure within a low-risk range. It is probably a result of regulated purine metabolism by quercetin, its microbial derivatives and their metabolites
