Polyphenols from Hibiscus sabdariffa calices were administered to patients with metabolic syndrome (125 mg/kg/day for 4 wk, n = 31) and spontaneously hypertensive rats (125 or 60 mg/kg in a single dose or daily for 1 wk, n = 8 for each experimental group). The H. sabdariffa extract improved metabolism, displayed potent anti-inflammatory and antioxidant activities, and significantly reduced blood pressure in both humans and rats. Diuresis and inhibition of the angiotensin I-converting enzyme were found to be less important mechanisms than those related to the antioxidant, anti-inflammatory, and endothelium-dependent effects to explain the beneficial actions. Notably, polyphenols induced a favorable endothelial response that should be considered in the management of metabolic cardiovascular risks. Additional supporting information may be found in the online version of this article at the publisher's web-site Keywords:The effects of different nutrients on metabolic syndrome are not completely understood [1,2]. Dietary management of hypertension, a key component, may prevent the onset of hypertensive events (systolic blood pressure (SBP) ≥ 135-140 mm Hg; diastolic blood pressure (DBP) ≥ 85-90 mm Hg) and improve or eradicate mild hypertension [3,4]. However, adherence to diets is usually not sustained, mainly because to receive high amounts of bioactive components from foods,