Review: absorption and metabolism of beta-carotene.

To better understand the potential function of beta-carotene (beta-C) in the prevention of cancer, greater knowledge of beta-C metabolism and a suitable animal model to mimic human beta-C metabolism are necessary. The small intestinal mucosa contains beta-C cleavage enzyme(s), thereby playing an important role in both the provitamin A activity and anti-cancer properties of beta-C. The ability of the ferret (Mustela putorius furo) to absorb intact beta-C makes it an appropriate model for studying human beta-C absorption. This article reviews the absorption and cleavage mechanisms of beta-C in both the human and the ferret. The biosynthesis of retinoic acid (RA) from beta-C via central and eccentric cleavage pathways is reviewed. The possible significance of the conversion of beta-C to RA as an anticancer mechanism is discussed.