Quercetin reduces systolic blood pressure and plasma oxidised low-density lipoprotein concentrations in overweight subjects with a high-cardiovascular disease risk phenotype: a double-blinded, placebo-controlled cross-over study

Abstract

Regular consumption of flavonoids may reduce the risk for CVD. However, the effects of individual flavonoids, for example, quercetin, remain unclear. The present study was undertaken to examine the effects of quercetin supplementation on blood pressure, lipid metabolism, markers of oxidative stress, inflammation, and body composition in an at-risk population of ninety-three overweight or obese subjects aged 25-65 years with metabolic syndrome traits. Subjects were randomised to receive 150 mg quercetin/d in a double-blinded, placebo-controlled cross-over trial with 6-week treatment periods separated by a 5-week washout period. Mean fasting plasma quercetin concentrations increased from 71 to 269 nmol/l (P,0·001) during quercetin treatment. In contrast to placebo, quercetin decreased systolic blood pressure (SBP) by 2·6 mmHg (P,0·01) in the entire study group, by 2·9 mmHg (P,0·01) in the subgroup of hypertensive subjects and by 3·7 mmHg (P,0·001) in the subgroup of younger adults aged 25 -50 years. Quercetin decreased serum HDL-cholesterol concentrations (P,0·001), while total cholesterol, TAG and the LDL:HDL-cholesterol and TAG:HDL-cholesterol ratios were unaltered. Quercetin significantly decreased plasma concentrations of atherogenic oxidised LDL, but did not affect TNF-a and C-reactive protein when compared with placebo. Quercetin supplementation had no effects on nutritional status. Blood parameters of liver and kidney function, haematology and serum electrolytes did not reveal any adverse effects of quercetin. In conclusion, quercetin reduced SBP and plasma oxidised LDL concentrations in overweight subjects with a high-CVD risk phenotype. Our findings provide further evidence that quercetin may provide protection against CVD.Quercetin: Blood pressure: Inflammation: Oxidised LDL: CVD Flavonoids in general and quercetin in particular have been associated with a decreased risk for CVD (1) . Furthermore, there was a trend towards a reduction in the incidence of type 2 diabetes mellitus at higher quercetin intakes (2) . In Western populations, the primary dietary sources of quercetin are tea, red wine, fruits and vegetables (3,4) . Quercetin is one of the major flavonoids, ubiquitously distributed in (edible) plants, and one of the most potent antioxidants of plant origin (1) . Numerous biological effects of quercetin, including antioxidant, anti-inflammatory, anti-thrombotic and vasodilatory actions, have been described in vitro (1) . However, quercetin intervention trials in human subjects have so far shown inconclusive and even conflicting results (5) . Quercetin supplementation increased plasma antioxidant capacity, ex vivo resistance of LDL to oxidation and resistance of lymphocyte DNA to strand breakage, but decreased urinary 8-hydroxy-2 0 -deoxyguanosine concentrations (5) . Other human studies, however, failed to confirm effects on these biomarkers (5) . A recent meta-analysis of 133 controlled flavonoid trials (6) suggested that there may be clinically relevant effects of some flavonoids or flavonoid-ri...

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