The consumption of cocoa and dark chocolate is associated with a lower risk of 
CVD, and improvements in endothelial function may mediate this relationship. 
Less is known about the effects of cocoa/chocolate on the augmentation index 
(AI), a measure of vascular stiffness and vascular tone in the peripheral 
arterioles. We enrolled thirty middle-aged, overweight adults in a randomised, 
placebo-controlled, 4-week, cross-over study. During the active treatment 
(cocoa) period, the participants consumed 37 g/d of dark chocolate and a 
sugar-free cocoa beverage (total cocoa = 22 g/d, total flavanols (TF) = 814 
mg/d). Colour-matched controls included a low-flavanol chocolate bar and a 
cocoa-free beverage with no added sugar (TF = 3 mg/d). Treatments were matched 
for total fat, saturated fat, carbohydrates and protein. The cocoa treatment 
significantly increased the basal diameter and peak diameter of the brachial 
artery by 6% (+2 mm) and basal blood flow volume by 22%. Substantial decreases 
in the AI, a measure of arterial stiffness, were observed in only women. 
Flow-mediated dilation and the reactive hyperaemia index remained unchanged. The 
consumption of cocoa had no effect on fasting blood measures, while the control 
treatment increased fasting insulin concentration and insulin resistance (P= 
0·01). Fasting blood pressure (BP) remained unchanged, although the acute 
consumption of cocoa increased resting BP by 4 mmHg. In summary, the 
high-flavanol cocoa and dark chocolate treatment was associated with enhanced 
vasodilation in both conduit and resistance arteries and was accompanied by 
significant reductions in arterial stiffness in women.