Vitamin A

Vitamin A is an essential human nutrient. It may be found in any of these forms:
 * retinol, the animal form of vitamin A, is a yellow fat-soluble, antioxidant vitamin with importance in vision and bone growth, it belongs to the family of chemical compounds known as retinoids.
 * other retinoids, a class of chemical compounds that are related chemically to vitamin A, are used in medicine.
 * carotenoids or other substances that enable the body to synthesize retinoids. Carotenoids are organic pigments that are naturally occurring in plants and some other photosynthetic organisms like algae, some types of fungus and some bacteria.