Quercetin-Rich Onion Skin Extract Lowers Blood Pressure in Overweight and Obese Patients

Written by Angeline A. De Leon, Staff Writer. Study finds that supplementation with 162 mg/d quercetin from onion skin extract lowers ambulatory blood pressure (ABP) in patients with hypertension, suggesting a cardioprotective effect of quercetin.

Quercetin is an antioxidant-rich plant pigment (flavonoid) found in red wines, apples, berries, and onions. Studies have linked dietary intake of flavonoids like quercetin with lower risk of cardiovascular disease (CVD), ¹ reduced platelet aggregation, ² and healthier cholesterol levels ³. The anti-inflammatory effects associated with quercetin ⁴ have been shown to help metabolic disorders, including insulin resistance and dyslipidemia, ⁵ and in patients at high risk of CVD, chronic supplementation with quercetin (at a dose of 150 mg/d) can reduce systolic blood pressure (SBP) ³. At pharmacological doses (between 500 to 730 mg/d), quercetin intake can also reduce BP in patients with hypertension and type 2 diabetes ⁶. Researchers hypothesize that the mechanisms underlying quercetin’s blood pressure-lowering effects may involve improvement of vascular function and/or reduction of oxidative stress, ⁷ but studies are ongoing. To date, the majority of human trials examining the cardioprotective effects of quercetin have also failed to measure ABP, which is considered to be the gold standard for BP measurement ⁸. Thus, a study ⁹ published by the British Journal of Nutrition investigated the relationship between quercetin intake and 24h ABP in overweight and obese subjects, also looking at the effects of supplementation on endothelial function.

A total of 68 overweight-to-obese (body mass index of 25-35 kg/m²) subjects (aged 25-65 years) with metabolic syndrome were enrolled in a randomized, double-blind, placebo-controlled cross-over trial. Participants were randomly assigned to ingest either 162 mg/d of quercetin from onion skin extract powder or matching placebo for 6 weeks before switching to the alternate arm of the study after a 6-week washout period. Along with office BP, 24h ABP and heart rate recordings were taken every 15 minutes during the daytime and every 30 minutes during nighttime before and after each intervention period. Fasting blood and urine samples were also collected, and endothelial function assessed using peripheral arterial tonometry technology.

Across all participants, quercetin was not seen to significantly impact 24h, day-time, or nighttime ABP nor office BP parameters. However, in a subgroup analysis of participants with stage 1 hypertension, supplementation with quercetin was associated with a significant decrease in 24h SBP (by –3.6 +/- 8.2 mmHg, p = 0.022), relative to placebo (mean treatment difference = -3.9 +/- 11.1 mmHg, p = 0.049). Quercetin also significantly reduced daytime SBP (by –4.6 +/- 9.0 mmHg, p = 0.014) and nighttime SBP (by –6.6 +/- 9.9 mmHg, p = 0.007) in stage 1 hypertensive subjects. Additionally, individuals receiving quercetin exhibited significantly lower 24h mean arterial pressure (MAP) (p = 0.043), daytime MAP (p = 0.042), and nighttime MAP (p = 0.001).

The first study to look at quercetin’s BP-lowering effects in relation to ABP, the current trial confirms that regular intake of quercetin-rich onion skin extract exerts a cardio-protective effect in overweight-to-obese individuals with pre-hypertension and stage 1 hypertension. Although no significant changes were observed in parameters related to endothelial function, inflammation, or lipid and glucose metabolism, supplementation with quercetin was related to a significant reduction in 24h systolic ABP. Although quercetin does appear to have significant cardioprotective effects, the mechanisms underlying its therapeutic impact still requires further investigation. A potential limitation of the present study pertains to the use of a quercetin-rich onion skin extract vs. pure quercetin, which may have introduced unknown dietary components that potentially influenced observed findings. Results, therefore, can only be exclusively applied to the proprietary extract used here and not quercetin as a pure, individual nutraceutical.

Source: Brull V, Burak C, Stoffel-Wagner B, et al. Effects of a quercetin-rich onion skin extract on 24h ambulatory blood pressure and endothelial function in overweight-to-obese patients with (pre-) hypertension: a randomised double-blinded placebo-controlled cross-over trial. British Journal of Nutrition. 2015; 114: 1263-1277. DOI: 10.1017/S0007114515002950.

© The Authors 2015. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/3.0/) , which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Posted February 25, 2020.

Angeline A. De Leon, MA, graduated from the University of Illinois at Urbana-Champaign in 2010, completing a bachelor’s degree in psychology, with a concentration in neuroscience. She received her master’s degree from The Ohio State University in 2013, where she studied clinical neuroscience within an integrative health program. Her specialized area of research involves the complementary use of neuroimaging and neuropsychology-based methodologies to examine how lifestyle factors, such as physical activity and meditation, can influence brain plasticity and enhance overall connectivity.

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