Bioavailability of the polyphenols: status and controversies

Abstract

The current interest in polyphenols has been driven primarily by epidemiological studies. However, to establish conclusive evidence for the effectiveness of dietary polyphenols in disease prevention, it is useful to better define the bioavailability of the polyphenols, so that their biological activity can be evaluated. The bioavailability appears to differ greatly among the various phenolic compounds, and the most abundant ones in our diet are not necessarily those that have the best bioavailability profile. In the present review, we focus on the factors influencing the bioavailability of the polyphenols. Moreover, a critical overview on the difficulties and the controversies of the studies on the bioavailability is discussed.

Keywords: bioavailability; dietary polyphenols; metabolites.

Figure 1.

The potential sites of the conjugation process of the polyphenols are schematically illustrated. The broken arrows represent the potential methylation sites; the full arrows represent the potential glucuronidation and sulfation sites.

Figure 2.

The absorption of dietary polyphenols in humans is schematically illustrated. The polyphenols are extensively modified during the absorption: the glycosides could be hydrolyzed in the small intestine or in the colon, and the released aglycones could be absorbed. Prior to the passage into the blood stream, the polyphenols undergo to other structural modifications due to the conjugation process, mainly in the liver.