Cocoa contains a high concentration of proanthocyanidins, phytonutrients belonging to the flavonoid group. Proanthocyanidins are biologically active in humans, and evidence suggests that they may protect from cardiovascular disease. Chemically, proanthocyanidins are polymers of the catechins found in green tea, and both catechins and proanthocyanidins decrease systemic oxidation in humans when regularly consumed in cocoa. In particular, cocoa may decreases platelet aggregation and prevent endothelial dysfunction as a result of its proanthocyanidin antioxidant effects. However, cocoa consumption is also able to raise levels of circulating high density lipoprotein (HDL) cholesterol, with high levels of HDL being associated with a reduced risk of cardiovascular disease. However, the mechanism by which the proanthocyanidins could affect lipoprotein levels is unclear. This has lead to speculation that other components within cocoa may be responsible for the beneficial effect on plasma HDL levels.
One of the components of cocoa that might be responsible for raising levels of HDL is the methylxanthines it contains. In particular, cacao contains theobromine and studies suggest that theobromine can favourably raise level of HDL. For example, in one study1, researchers compared the HDL modulating effect of isolated theobromine in comparison to cocoa powder in a double-blind randomised, placebo controlled study. Subject participating in the study consumed either 200 mL of a cocoa drink containing 150 mg theobromine and 325 mg of flavonoids (mostly as proanthocyanidins), 200 mL of a drink containing 850 mg of isolated theobromine, or 200 mL of a cocoa drink with added theobromine containing a total of 1000 mg theobromine and 325 mg flavonoids. A control group received a placebo drink. The results showed that theobromine, but not the flavonoids, caused a significant and large increase in plasma HDL and a moderate but significant descrease in plasma low density lipoprotein (LDL) cholesterol.
The increase in HDL and decrease in LDL seen with theobromine was reflected in changes to apolipoprotein A-I and apolipoprotein B, the main protein components of HDL and LDL, respectively. Therefore theobromine is effective at favourably modulating the plasma lipoprotein ratio which may explain some of the cardioprotective effects of cocoa. The HDL raising effects seen in this study are similar to those seen with a reduction in body weight of around 5 to 10 % and are therefore clinically relevant and practically beneficial. Although the effect on LDL was more modest, the fall still further improved the HDL to LDL ratio, arguably a better predictor of cardiovascular risk that either measure alone. The authors of the study did not investigate the reason for the beneficial lipoprotein effect of theobromine and could not explain the mechanisms. However, post hoc analysis did show no effect of theobromine on the cholesterol ester transfer protein, suggesting that changes to CETP were not the reason for the changes.
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