ABSTRACT
The absorption of carotenoids, vitamin A precursors, from dietary sources requires sufficient digestion of food to release carotenoids, and the formation of mixed micelles in the small intestine, aided by the presence of dietary fat and secretion of bile. Fat-soluble vitamin A is an essential factor for vision, growth and reproduction of all vertebrate animals, including humans. It is derived from certain carotenoid pigments synthesized by plants, long-chained hydrocarbon compounds, constructed of eight 5-carbon isoprene units. Vitamin A, oxidized irreversibly to retinoic acid, is required for differentiation of epithelial tissues, including cornea and conjunctival membranes of the eye. A great majority of the available studies reported total vitamin A intake without specifying the proportion obtained from animal and plant sources, and many used International Units, which only added to the confusion when reporting total vitamin A intake fro.
