The Acute Effect of Dark Chocolate on Blood Pressure and Renal Hemodynamics as Assessed With Doppler Ultrasound in Healthy Volunteers

OBJECTIVE: Dark chocolate (DC) is rich in cocoa, a substance with antioxidative and antihypertensive properties. The effect of DC on renal hemodynamics is poorly understood. The aim of this randomized, placebo-controlled study was to investigate whether DC induces changes in blood pressure (BP) and renal perfusion, as assessed with Doppler ultrasound - both at rest and during sympathetic stimulation - compared to cocoa-free white chocolate (WC). METHODS: Seventeen healthy volunteers aged 42 ± 14 years (47% women) were randomized to eat 1 dose of 1 g/kg of DC (70% cocoa) or 1 g/kg of WC. The renal resistive index (RRI), a proxy of intra-renal vascular resistance, was measured just before and 2 hours after chocolate consumption. BP, heart rate, and cardiac output were measured with the Finapres NOVA hemodynamic monitoring system. At each time point, a 3-minute handgrip (HG) test was performed as sympathetic stimulus; during the HG, supplementary RRI values were measured. Two weeks later, the same exams were repeated with the other type of chocolate. RESULTS: DC intake decreased RRI from 0.62 ± 0.04 to 0.60 ± 0.04 (P = .039), whereas RRI did not change after the intake of WC (before: 0.62 ± 0.05, after: 0.62 ± 0.04, P = .47). DC had no effect on BP in participants consuming >50 g chocolate/week, whereas systolic blood pressure increased from 115 ± 17 to 122 ± 15 mmHg (P = .02) in nonregular chocolate eaters. HG exercise lowered the RRI from 0.62 ± 0.04 to 0.57 ± 0.05 (P = .001) and prolonged acceleration times (from 48.2 ± 8.2 to 57.8 ± 14 msec, P = .009), while increasing BP, heart rate, and cardiac output. In participants aged ≥35 years, the effect of HG exercise on RRI was attenuated by DC ingestion. CONCLUSIONS: The ingestion of DC led to an acute reduction in RRI, suggesting intra-renal vasodilation, whereas WC had no effect. BP only increased in nonregular DC eaters, suggesting that regular DC eaters accustomed to the BP-modifying effects of DC. HG exercise led to a tardus parvus-like pattern of Doppler curves. This effect was attenuated by DC in older participants, suggesting that DC counterbalances the sympathetically induced intra-renal vasoconstriction in these volunteers.