Effects of a quercetin-rich onion skin extract on 24 h ambulatory blood pressure and endothelial function in overweight-to-obese patients with (pre-)hypertension: a randomised double-blinded placebo-controlled cross-over trial
What this study found
Quercetin did not significantly improve 24 h ambulatory blood pressure, office blood pressure, endothelial function, or inflammatory and oxidative markers in the total study population. In the hypertensive subgroup, quercetin lowered mean 24 h systolic BP by -3.6 (SD 8.2) mmHg from baseline (P = 0.022) and the treatment difference versus placebo was -3.9 (SD 11.1) mmHg (P = 0.049). Day-time systolic BP decreased by -4.6 (SD 9.0) mmHg (P = 0.014) and night-time systolic BP decreased by -6.6 (SD 9.9) mmHg (P = 0.007). No adverse events were reported during either treatment.
- Study & population
- Randomised, double-blinded, placebo-controlled crossover trial in overweight-to-obese adults with pre-hypertension or stage I hypertension recruited from the community in Bonn, Germany.
- Intervention
- Participants received a quercetin-rich onion skin extract orally at 162 mg quercetin per day, given as three capsules daily with the principal meals for 6 weeks.
- Key limitation
- The overall sample was small, and the main blood pressure benefit appeared only in an exploratory hypertensive subgroup analysis.
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Open PDFOriginal abstract
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.