Epidemiological studies report that
quercetin, an
antioxidant flavonol found in apples, berries, and onions, is associated with reduced risk of
coronary heart disease and
stroke.
Quercetin supplementation also reduces blood pressure in hypertensive rodents. The efficacy of
quercetin supplementation to lower blood pressure in hypertensive humans has never been evaluated. We tested the hypothesis that
quercetin supplementation reduces blood pressure in hypertensive patients. We then determined whether the
antihypertensive effect of
quercetin is associated with reductions in systemic
oxidant stress. Men and women with
prehypertension (n = 19) and stage 1
hypertension (n = 22) were enrolled in a randomized, double-blind, placebo-controlled, crossover study to test the efficacy of 730 mg
quercetin/d for 28 d vs. placebo. Blood pressure (mm Hg, systolic/diastolic) at enrollment was 137 +/- 2/86 +/- 1 in prehypertensives and 148 +/- 2/96 +/- 1 in stage 1 hypertensive subjects. Blood pressure was not altered in prehypertensive patients after
quercetin supplementation. In contrast, reductions in (P < 0.01) systolic (-7 +/- 2 mm Hg), diastolic (-5 +/- 2 mm Hg), and mean arterial pressures (-5 +/- 2 mm Hg) were observed in stage 1 hypertensive patients after
quercetin treatment. However, indices of
oxidant stress measured in the plasma and urine were not affected by
quercetin. These data are the first to our knowledge to show that
quercetin supplementation reduces blood pressure in hypertensive subjects. Contrary to animal-based studies, there was no
quercetin-evoked reduction in systemic markers of oxidative stress.