Vitamin A can come from plant or animal sources. Plant sources include colorful fruits and vegetables. Animal sources include liver and whole milk. Vitamin A is also added to foods like cereals. This vitamin is fat-soluble vitamin (like D, E and K, too).
Vitamin A regulates the growth and differentiation of many cells and tissues. It primarily affects the mucous membranes of the respiratory tract. Prolonged Vitamin A deficiency results in metaplasia of the respiratory epithelium, a pre cancer condition. Also controls the morphogenesis of many tissues during embryonic development.
Vegetarians, young children, and alcoholics may need extra Vitamin A. If you have certain conditions, such as liver diseases, cystic fibrosis, and Crohn's disease, you might also need more vitamin A.