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

The British Journal of Nutrition
Q1
Sep 2015
Citations:186
Influential Citations:6
Interventional (Human) Studies
93
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Methods
Double-blinded, randomized, placebo-controlled cross-over trial; overweight-to-obese adults (BMI 25–35 kg/m2) aged 25–65 years with pre-hypertension or stage I hypertension; 70 randomized, 68 completed (34 men, 34 women); some participants used antihypertensive (n=12) or thyroid medications (n=9) and continued; 6-week treatment periods separated by a 6-week washout.
Intervention
Quercetin-rich onion skin extract powder; 162 mg quercetin per day (three capsules per day, each capsule containing 54 mg quercetin from onion skin extract); onion skin extract powder per capsule = 132 mg; duration = 6 weeks; taken with principal meals.
Results
Total group showed no significant effects on 24 h ambulatory BP or office BP. In hypertensive participants, quercetin lowered mean 24 h SBP by 3.6 mmHg versus placebo (P=0.022) with a treatment difference of −3.9 mmHg (P=0.049). Day-time SBP decreased by 4.6 mmHg (P=0.014) and night-time SBP by 6.6 mmHg (P=0.007); inter-group differences significant for 24 h SBP (P=0.049) and night-time SBP (P=0.021). No significant changes in endothelial function markers or other biomarkers (endothelin-1, sICAM-1, sVCAM-1, ADMA, ACE, CRP, oxLDL, isoprostanes). Conclusion: Regular intake of 162 mg/d quercetin from onion skin extract lowers ambulatory BP in hypertensive overweight-to-obese adults, suggesting cardioprotective potential, but mechanisms remain unclear and effects did not extend to the total population.
Limitations
Onion skin extract contains other polyphenols; results may not apply to pure quercetin. Exploratory analyses with multiple comparisons raise possibility of chance findings. Cross-over design and per-protocol analysis; some participants on antihypertensives or thyroid meds; short duration (6 weeks); limited generalizability to overweight/obese adults with pre-hypertension or stage I hypertension.

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 ...