People suffering from hypertension may benefit from taking a dietary supplement made from onion skins. Researchers from the University of Bonn, Germany, studied the effects of taking a dietary supplement of the polyphenol quercetin, which is derived from onion skins, on blood pressure in overweight-and-obese patients with pre-hypertension and stage I hypertension. A total of 70 subjects were randomised to receive 162 mg/d quercetin from onion skin extract powder or placebo for 6-weeks. Results showed that the quercetin supplement decreased 24-hour systolic blood pressure by 3·6 mmHg when compared with placebo. The supplement also significantly decreased day-time and night-time systolic blood pressure in participants with hypertension. Blood pressure changes in non-hypertensive participants were not significant. The authors note that quercetin had no effect on numerous 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. The authors concluded: “Supplementation with 162 mg/d quercetin from onion skin extract lowers ambulatory blood pressure in patients with hypertension, suggesting a cardioprotective effect of quercetin. The mechanisms responsible for the blood pressure-lowering effect remain unclear.” Quercetin is found in onions, kale, apple skins, berries, citrus fruits and tea.