Vitamin a

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Vitamin A
Retinoic acid, or Vitamin A, is an essential human nutrient referring to a family of similarly shaped molecules called the retinoids. Its discovery dates back to research done in 1906, which indicated that factors other than carbohydrates, proteins, and fats were necessary to keep cattle healthy. Vitamin A was independently discovered by Elmer McCollum at the University of Wisconsin-Madison, and Lafayette Mendel and Thomas Osborne at Yale University. It was named due to the fact that the “water-soluble factor B” (Vitamin B) had just recently been discovered and therefore researchers chose the name “fat-soluble factor A” (Vitamin A).

Vitamin A does not a take on a very complex structure. “Retinol is the immediate precursor to two important active metabolites: retinal, which plays a critical role in vision, and retinoic acid, which serves as an intracellular messenger that affects transcription of a number of genes.” (Lancet, 1995) It is structurally related to carotene. “Carotene is converted into Vitamin A in the liver.” (Harrison, 1997) An oxidative splitting of beta carotene occurs in the small intestine. “Two molecules of Vitamin A are formed from on molecule of beta carotene.” (Harrison, 1997)

Retinol plays a role in a variety of functions in the human body. They include the following: vision, gene transcription, immune function, embryonic development and reproduction, bone metabolism, hematopoiesis, skin health, reducing the risk of heart disease and cancer, and antioxidant activity. For vision, “Retinal is a necessary structural component of rhodopsin or visual purple, the light sensitive pigment within rod and cone cells of the retina. If inadequate quantities of vitamin A are present, vision is impaired.” (Lancet, 1995) In terms of genes, retinoic acid and its isomers act as hormones to affect gene expression and thereby influence numerous physiological processes. Vitamin A is commonly known as the anti-infective vitamin, because it is...
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