OBJECTIVE: Dark chocolate (DC) is rich in cocoa, a substance with anti-oxidative 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 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 one dose of 1g/kg of DC (70% cocoa) or 1g/kg of WC. The renal resistive index (RRI), a proxy of intra-renal vascular resistance, was measured just before and two hours after chocolate consumption. Blood pressure (BP), heart rate and cardiac output were measured with the Finapres® NOVA hemodynamic monitoring system. At each time point, a 3-minute handgrip test was performed as sympathetic stimulus
during the handgrip, 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=0.039), whereas RRI did not change after the intake of WC (before: 0.62±0.05, after: 0.62±0.04, p=0.47). DC had no effect on BP in participants consuming >
50g chocolate/week, whereas SBP increased from 115±17 to 122±15 mmHg (p=0.02) in non-regular chocolate eaters. Handgrip exercise lowered the RRI from 0.62±0.04 to 0.57±0.05 (p=0.002) and prolonged acceleration times (from 48.2±8.2 to 57.8±14 msec, p=0.009), while increasing BP, heart rate and cardiac output. In participants aged ≥35 years, the effect of handgrip 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 non-regular DC eaters, suggesting that regular DC eaters accustomed to the BP-modifying effects of DC. Handgrip 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.