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 - PubMed (original) (raw)

Randomized Controlled Trial

. 2015 Oct 28;114(8):1263-77.

doi: 10.1017/S0007114515002950. Epub 2015 Sep 2.

Constanze Burak 1, Birgit Stoffel-Wagner 2, Siegfried Wolffram 3, Georg Nickenig 4, Cornelius Müller 4, Peter Langguth 5, Birgit Alteheld 1, Rolf Fimmers 6, Stefanie Naaf 7, Benno F Zimmermann 7, Peter Stehle 1, Sarah Egert 1

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Randomized Controlled Trial

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

Verena Brüll et al. Br J Nutr. 2015.

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.

Keywords: ABP ambulatory blood pressure; ACE angiotensin-converting enzyme; ADMA asymmetric dimethylarginine; BP blood pressure; Blood pressure; Cardiovascular diseases; DBP diastolic blood pressure; Endothelial function; Hypertension; IsoP isoprostanes; MAP mean arterial pressure; PAT peripheral arterial tonometry; Quercetin; RHI reactive hyperaemia index; SBP systolic blood pressure; oxLDL oxidised LDL; sICAM-1 soluble intercellular adhesion molecule 1; sVCAM-1 soluble vascular cell adhesion molecule 1.

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Figures

Fig. 1

Fig. 1

Flow diagram of participants. ABP, ambulatory blood pressure; BP, blood pressure.

Fig. 2

Fig. 2

Fasting plasma concentrations of quercetin (a) (n 68) and total flavonols (b) (n 68) before and after the 6-week supplementation with quercetin (162 mg/d; ■) or placebo (□). Values are means and standard deviations represented by vertical bars. *** Mean value was significantly different from baseline (P<0·0001; intra-group comparison). † Change during quercetin treatment was significantly different from change during placebo treatment (P<0·0001; inter-group comparison). Total plasma flavonols were calculated as follows: total flavonols (nmol/l)=quercetin (nmol/l)+kaempferol (nmol/l)+isorhamnetin (nmol/l)+tamarixetin (nmol/l). The two groups did not differ significantly with regard to plasma concentrations of quercetin and total flavonol at baseline (Wilcoxon signed-rank tests).

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