Abstract
- Background
Quercetin, a prominent dietary polyphenol, possesses recognized antihypertensive and vasorelaxant properties that suggest a strong potential for cardiovascular disease (CVD) prevention. This randomized, double-blind, placebo-controlled, crossover trial was designed to investigate the effects of regular dietary intake of quercetin on blood pressure (BP) among overweight-to-obese patients presenting with pre-hypertension and stage 1 hypertension. Furthermore, the study aimed to explore potential underlying physiological and biochemical mechanisms responsible for the hypothesized blood-pressure-lowering effects of quercetin.
- Methods
A rigorous double-blind, placebo-controlled crossover trial was conducted involving 70 adult subjects randomized to receive either 162 mg/day of quercetin derived from onion skin extract powder or a matched placebo. The intervention comprised two 6-week treatment periods separated by a 6-week washout phase. Comprehensive physiological and biochemical evaluations were performed pre- and post-intervention, including 24-hour ambulatory blood pressure (ABP) monitoring, office-based blood pressure measurements, EndoPAT-assessed endothelial function, and analyses of systemic blood and urine samples for vasoactive, oxidative, inflammatory, lipid, and glucose metabolic biomarkers.
- Results
In the total study cohort, daily quercetin supplementation did not produce statistically significant alterations in 24-hour ABP parameters or office blood pressure. However, within the predefined hypertensive subgroup, quercetin supplementation significantly decreased 24-hour systolic blood pressure by $-3.6$ mm Hg ($P = 0.022$) relative to baseline, with a mean treatment difference of $-3.9$ mm Hg ($P = 0.049$) compared to the placebo condition. Additionally, quercetin reduced daytime and nighttime systolic blood pressure levels within the hypertensive cohort, although between-group comparisons for these specific time blocks did not reach statistical significance. Across both the total group and the hypertensive subgroup, secondary markers—including vasoactive biomarkers (endothelin-1, soluble endothelial-derived adhesion molecules, asymmetric dimethylarginine, angiotensin-converting enzyme activity), endothelial function, and parameters of oxidation, inflammation, lipid, and glucose metabolism—remained unaffected by the quercetin intervention.
- Conclusions
Supplementation with 162 mg/day of quercetin via an onion skin extract effectively lowers ambulatory blood pressure in patients with clinical hypertension, indicating a meaningful cardioprotective effect. Nonetheless, the precise biochemical mechanisms mediating this blood-pressure-lowering efficacy remain to be fully elucidated.
https://pmc.ncbi.nlm.nih.gov/articles/PMC4594049/