ABSTRACT
Vitamin A-active compounds are represented by retinoids (designated as vitamin A) and their carotenoid precursors (provitamin A carotenoids). The retinoids comprise retinol, retinaldehyde, and retinoic acid, together with their naturally occurring and synthetic analogs. Generally speaking, dietary vitamin A is obtained from animal-derived foods, while plant foods provide carotenoid precursors.
