I4 Factors affecting bioavailability of plant polyphenols

Abstract

Nowadays plant polyphenols attract much attention in the prevention of chronic diseases. Epidemiological and intervention studies strongly suggest that polyphenol intake has beneficial effects on vascular health. It is unlikely that polyphenols act as direct antioxidants, although oxidative stress profoundly contributes to vascular impairment leading to cardiovascular diseases. Polyphenols, in particular, low-molecular weight flavonoids may exert their function by tuning the cellular redox state to an adaptive response or tolerable stress. However, the optimum intake of flavonoids from supplements or diet has not been clarified yet, because a number of exogenous and endogenous factors modulating their bioavailability affect their vascular function. This lecture will focus on the current knowledge of the bioavailability and its consequence on vascular function of an antioxidative flavonoid quercetin. Current intervention studies imply that intake of quercetin-rich onion improves vascular health. Onion may be superior to quercetin supplement from the viewpoint of quercetin bioavailability, probably because the food matrix enhances the intestinal absorption of quercetin. a-Glucosylation increases its bioavailability by elevating the accessibility to the absorptive cells. Prenylaton may enhance bioaccumulation at the target site by increasing the cellular uptake. However, these chemical modifications do not guarantee health benefits to the vascular system. Although dietary quercetin is exclusively present as their conjugated form in the blood stream, its vascular function seems to be mediated by inflammation-dependent deconjugation reaction. Finally, bioavailability of non-absorptive polyphenols to microbiota in the gut should be pointed out, as the colonic microbiota is regarded as a separate organ within the human host.