Mammalian carotenoid absorption and metabolism

Carotenoids are purported to provide widespread function in the biology and health of humans and other mammalian species. Provitamin A carotenoids, such as β-carotene, are valued in the diet of many mammals for their contribution as precursors of vitamin A and retinoids. Carotenoids may also function in the prevention of some chronic diseases by improving intercellular communication, enhancing immune response, and operating as antioxidants in vivo. It is widely known that humans and other mammalian species absorb and accumulate carotenoids in body tissues. However, the potential use of carotenoids as modulators of disease and in the prevention of vitamin A deficiency has been hindered by the limited progress in understanding carotenoid absorption and metabolism. In fact, major gaps in knowledge still exist in the fundamental pathways beginning with release from the food matrix and ending with distribution in body tissues and excretion. Continued development of assessment methods for humans, appropriate animal models for mechanistic studies, and analytical techniques for quantification and identification of compounds is needed to advance our understanding of these critical pathways. This review will discuss the current knowledge involving the fundamental pathways of absorption and metabolism of carotenoids in mammalian species. When applicable, emphasis will be placed on the human.