Vitamin A and provitamin A carotenoids

Summary Vitamin A is an essential micronutrient required to maintain vision, the immune response, barrier function, growth and differentiation, male and female reproduction, and fetal development. It is acquired from the diet either as preformed vitamin A from animal foods or as provitamin A carotenoids acquired from plant foods. Vitamin A actions in the body involve two biochemical mechanisms. Its role in vision involves 11-cis-retinaldehyde, which is the chromophore for the visual pigment rhodopsin. The other involves all-trans-retinoic acid serving as a ligand for three distinct retinoic acid nuclear receptors, which regulate transcription of literally hundreds of genes. Vitamin A deficiency remains a major public health problem in the developing world. The vitamin and related factors are implicated in the causation/prevention of human metabolic disease, including obesity, diabetes, hepatic disease, and cardiovascular disease, as well as proliferative disorders, including cancers and skin disease.