Carotenoid interactions.

Interactions between carotenoids during absorption and during postabsorptive metabolism have been demonstrated or suggested in animal and human feeding or supplementation studies, as well as in in vitro studies of intestinal beta-carotene cleavage. Much of the evidence suggests an interaction between beta-carotene and oxycarotenoids such as canthaxanthin and lutein, and between the hydrocarbon carotenoids beta-carotene and lycopene. The evidence is equivocal, however, with discrepant findings between studies, both in magnitude and in direction of the interactions observed. This review discusses studies of carotenoid interactions and explores the possible underlying mechanisms and implications of these interactions. The most likely explanations for carotenoid interactions appear to be competition for incorporation into micelles, carotenoid exchange between lipoproteins in the postprandial state, and inhibition of provitamin A (beta-carotene) cleavage.