One study found that black tea, green tea, red wine, and cocoa are all rich in phenolic phytochemicals, theaflavins, resveratrol, and proanthocyanidins, respectively. They have been extensively studied due to their general antioxidant properties, possibly as chemopreventive agents.
Cocoa is higher in total phenolics and has the highest antioxidant activity. These results suggest that cocoa powder is more beneficial to health than tea and red wine.
Another study found that eating lots of fruits and vegetables may reduce the risk of coronary heart disease and stroke, but a similar association was found with cocoa, a "naturally rich food in polyphenols."
Several intervention studies have strongly suggested that cocoa provides a variety of cardiovascular health benefits, such as lowering blood pressure, improving vascular function and glucose metabolism, and reducing platelet aggregation and adhesion.
It is thought that cocoa exerts its positive effects through mechanisms including activation of nitric oxide synthase, increased nitric oxide bioavailability, and antioxidant and anti-inflammatory properties.