Bioavailability of dietary flavonoids and carotenoids

Dietary antioxidants may help to supplement the body antioxidant defenses in handling free radicals. Studies on different food sources to discover their antioxidant property have received considerable attention since 1960s. However, the majority of these studies were from epidemiological studies and in vitro experiments. There are much fewer in vivo studies on the bioavailability of consumed antioxidants. Bioavailability of antioxidants is important, as the in vitro data cannot be simply extrapolated to the physiological situation. Hence, it is not convinced that dietary antioxidants can act as supplemental free radical scavengers to the body. Carotenoids and flavonoids are among the most extensively studied phytochemicals and were first reported to have antioxidant effects in the late 1970s and mid-1980s, respectively. The present review summarizes the existing bibliography over the last few decades on bioavailability studies of carotenoids and flavonoids, both in human and in rodents. Those findings well implied that it is extremely necessary to increase the bioavailability study of antioxidants so as to demonstrate direct absorption of antioxidants in vivo and, thus enable a more definite conclusion to be drawn on the beneficial effects that dietary antioxidants may have on the body.