(A) Feasibility study: double-masked, randomized study design to test acute effects (red) of a single ingestion of flavanol-containing cocoa in diabetic patients, and to assess dosage regimens for long-term studies. Flow-mediated dilation (FMD) and hemodynamics were measured before and up to 6 h after consumption of a single cocoa drink available at 3 different flavanol doses (high: 963 mg of flavanols = red square; medium: 371 mg = red triangle; or control: 75 mg = red circle). Plasma flavanol metabolites were measured before and 2 h after cocoa intake. Each cocoa ingestion was separated by at least 3 days to avoid potential carry-over effects. (B) Efficacy study: double-masked, randomized, controlled, parallel-group study design to investigate the sustained effects (green) of regular daily cocoa intake on endothelial function in diabetic patients. Patients were randomized to receive cocoa containing either a cumulative dose of 963 mg of flavanols (treatment group: 3 x 321 mg daily = green squares) or 75 mg of flavanols (control group: 3 x 25 mg daily = green circles). Flow-mediated dilation, hemodynamic parameters, and plasma flavanol metabolites were measured 1 h before and 2 h after the morning cocoa drink at study entry (day 0), after 1 week (day 8), and after 1 month (day 30).

This double-masked, randomized trial, designed to study the effects of a dietary intervention on vascular function in diabetic patients, consisted of a feasibility study and a consecutive efficacy study. Ten patients were randomized into the feasibility study. For the efficacy study, 44 patients were assigned to either the control or the treatment group, receiving a cumulative daily dose of flavanols of 75 mg (control group) and 963 mg (treatment group), respectively.

For a detailed protocol of the feasibility study, refer to Figure 1A. Baseline values (black) for flow-mediated dilation (FMD) were similar in all groups at study entry. After ingestion of the cocoa drinks, containing either a medium (371 mg; red triangles) or a high (963 mg; red squares) dose of flavanols, FMD increased significantly, while the ingestion of the control drink (75 mg of flavanols; red circles) had no effect. Data are given as mean ± standard deviation. *Indicates significant differences in FMD compared with that seen in baseline within each group, p < 0.05; #Indicates significant differences in FMD between the control and the high-flavanol dose, p < 0.05.

Two hours after the consumption of a cocoa drink containing 963 mg of flavanols at study entry (black squares), every study participant exhibited an increase in flow-mediated dilation (FMD) and in plasma flavanol metabolites levels, demonstrating acute effects (red squares), and supporting the conjecture that a daily intake of a cumulative dose of 963 mg of flavanols may be sufficient to induce a sustained improvement in vascular function over time.

For a detailed study protocol of the efficacy study refer to Figure 1B. At study entry (black), baseline values for flow-mediated dilation (FMD) were similar in both groups. In the treatment group (squares), FMD was significantly augmented over time. On top of sustained FMD increases (green), acute improvements (red) were observed at 2 h after ingestion of flavanol-containing cocoa. No significant changes could be observed in the control group (circles). Data are given as mean ± standard deviation. *Indicates significant differences in FMD compared with baseline differences within each group, p < 0.001; #Indicates significant differences in FMD between the control group and the treatment group, p < 0.05.