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Br J Nutr. 2015 Oct 28;114(8):1263-77. doi: 10.1017/S0007114515002950. Epub 2015 Sep 2.

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.

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1Department of Nutrition and Food Sciences,Nutritional Physiology,University of Bonn,53115 Bonn,Germany.
2Institute of Clinical Chemistry and Clinical Pharmacology,University Hospital Bonn,53127 Bonn,Germany.
3Institute of Animal Nutrition and Physiology,Christian-Albrechts-University Kiel,24118 Kiel,Germany.
4Department of Cardiology,Angiology and Pneumology,University Hospital Bonn,53127 Bonn,Germany.
5Department of Biopharmaceutics and Pharmaceutical Technology,Institute of Pharmacy and Biochemistry,Johannes Gutenberg University Mainz,55099 Mainz,Germany.
6Institute of Medical Biometry,Informatics and Epidemiology,University Hospital Bonn,53127 Bonn,Germany.
7Institut Prof. Dr. Georg Kurz GmbH,50933 Köln,Germany.


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.


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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