However the uptake of flavonols in humans could be increased significantly by concurrent consumption of carbohydrates. Furthermore, lipid and protein rich meals did not affect the bioavailability of cocoa polyphenols. Cocoa powder dissolved in milk, as one of the most common ways of cocoa powder consumption, did not change the bioavailability of cocoa powder flavonoids in healthy humans. The food matrix seems to be an important factor that may affect the bioavailability of cocoa polyphenols. This may explain the relatively low bioavailability of catechins from chocolate and cocoa-containing products. Donovan and coworkers demonstrated that commercial chocolate samples available around the world contain a predominance of the less bioavailable (−)-catechin enantiomer as compared to the (+)-catechin which is present in most other plant derived foods. Plasma concentrations of cocoa polyphenols were often in the nanomolar or low micromolar range. The peak plasma concentration of flavonols was determined 2–3 hours after ingestion.
Monomeric flavonoids as well as dimeric and trimeric procyanidins have been detected in human plasma after consumption. Polyphenols were given as cocoa rich beverages or chocolate. The bioavailability of cocoa polyphenols has been measured in several studies in humans ( Table 1). The biological activity of cocoa polyphenols largely depend on their bioavailability. In order to determine potential health benefits of cocoa polyphenols large scale, long term, randomized, placebo controlled studies, (ideally with a cross-over design) as well as prospective studies are warranted. If dietary cocoa polyphenol intake is due to chocolate its high energy content needs to be taken into account. Human studies regarding the effect of cocoa polyphenols on vascular health are often underpowered and lack a rigorous study design.
Bioavailability studies indicate that plasma concentrations of cocoa polyphenols following dietary intake are low and in the nanomolar range. However cocoa polyphenol concentrations, as used in many cell culture studies, are not physiologically achievable. Several molecular targets (e.g., nuclear factor kappa B, endothelial nitric oxide synthase, angiotensin converting enzyme) have been recently identified which may partly explain potential beneficial cardiovascular effects of cocoa polyphenols. In vitro as well as cell culture data indicate that cocoa polyphenols may exhibit antioxidant and anti-inflammatory, as well as anti-atherogenic activity. Cocoa is a rich source of dietary polyphenols.
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