Abstract
The polyphenol quercetin may prevent CVD due to its antihypertensive and vasorelaxant properties. We investigated the effects of quercetin after regular intake on blood pressure (BP) in overweight-to-obese patients with pre-hypertension and stage I hypertension. In addition, the potential mechanisms responsible for the hypothesised effect of quercetin on BP were explored. Subjects (n 70) were randomised to receive 162 mg/d quercetin from onion skin extract powder or placebo in a double-blinded, placebo-controlled cross-over trial with 6-week treatment periods separated by a 6-week washout period. Before and after the intervention, ambulatory blood pressure (ABP) and office BP were measured; urine and blood samples were collected; and endothelial function was measured by EndoPAT technology. In the total group, quercetin did not significantly affect 24 h ABP parameters and office BP. In the subgroup of hypertensives, quercetin decreased 24 h systolic BP by -3·6 mmHg (P=0·022) when compared with placebo (mean treatment difference, -3·9 mmHg; P=0·049). In addition, quercetin significantly decreased day-time and night-time systolic BP in hypertensives, but without a significant effect in inter-group comparison. In the total group and also in the subgroup of hypertensives, vasoactive biomarkers including endothelin-1, soluble endothelial-derived adhesion molecules, asymmetric dimethylarginine, angiotensin-converting enzyme activity, endothelial function, parameters of oxidation, inflammation, lipid and glucose metabolism were not affected by quercetin. In conclusion, supplementation with 162 mg/d quercetin from onion skin extract lowers ABP in patients with hypertension, suggesting a cardioprotective effect of quercetin. The mechanisms responsible for the BP-lowering effect remain unclear.
Highlights
Quercetin (3,3′,4′,5,7-pentahydroxyflavone) is one of the predominant flavonoids, ubiquitously distributed in plants, and one of the most potent antioxidants of plant origin[1]
One limitation in the interpretation of the BP-lowering effect of chronic quercetin supplementation is that all human studies published to date, including our own trial[7], only measured the office BP in the resting state and did not integrate an ambulatory blood pressure (ABP) monitoring
The superior predictive power of ABP monitoring is probably due to its higher number of readings, which increases the reliability of the measurement, and due to its ability to capture the impact of stressors and other environmental factors that occur in daily life and are likely to affect BP[16]
Summary
Quercetin (3,3′,4′,5,7-pentahydroxyflavone) is one of the predominant flavonoids, ubiquitously distributed in (edible) plants, and one of the most potent antioxidants of plant origin[1]. As demonstrated in cohort studies, dietary intake of flavonoids in general and of quercetin in particular is associated with a decreased risk for CVD[2,4]. One limitation in the interpretation of the BP-lowering effect of chronic quercetin supplementation is that all human studies published to date, including our own trial[7], only measured the office (clinic) BP in the resting state (typically in the morning while fasting) and did not integrate an ambulatory blood pressure (ABP) monitoring. The aim of the present double-blinded, placebocontrolled cross-over trial was to systematically investigate the effects of quercetin on arterial BP (office BP and 24 h ABP profiles) in adults with pre-hypertension and stage I hypertension, and to explore mechanisms involved in the BP-lowering efficacy of quercetin. Effects of quercetin on lipid and glucose metabolism were investigated
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