Introduction and Index Vitamins are organic molecules that are necessary for normal metabolism in animals, but either are not synthesized in the body or are synthesized in inadequate quantities. Consequently, vitamins must be obtained from the diet.
Most vitamins function as coenzymes or cofactors.
Deficiency states are recognized for all vitamins, and in many cases, excessive intake also leads to disease. Present in many animal tissues, especially fish and liver. Carotinoids in green plants serve can be converted to vitamin A following ingestion. Necessary for a broad range of bodily function, including production of vision pigments, resistance to infectious agents and maintenance of health in many epithelial cells. Disease results from both deficiency and excess.