Vitamin A occurs as two principal forms in foods: 1) retinoids, found in animal-sourced foods, either as retinol or bound to a fatty acid to become a retinyl ester, and 2) the carotenoids ?-carotene (alpha-carotene), ?-carotene, ?-carotene (gamma-carotene), and the xanthophyll beta-cryptoxanthin (all of which