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).
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.
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=0.001) 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.
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.