Vitamin A was the first vitamin identified and from that discovery there has been a 40 plus year search to identify every compound that can fit in the category. Vitamin A is a generic term for a group of entities that include retinal compounds and the pro-vitamin beta carotene.
Preformed vitamin A (the vitamin in its natural state) is found in foods of animal origin, such as liver and egg yolks. The pro-vitamin beta-carotene can be found only in foods of plant origins. Beta carotene is one of almost 600 carotenoids, 50 of which display some A activity. One form, all-trans beta carotene has the greatest A activity.
Vitanin A requires some fat to be present in the digestive tract in order to be absorbed, and goes into the system better (more readily) than carotenoids. Absorption is diminished in the presence of intestinal disorders that impair proper digestion and absorption of fats. The product Retinyl palmitate is one form of A that is absorbed even during a deficiency of dietary fat, thus making it useful in management of long-term intestinal disorders like sprue, cystic fibrosis, and celiac disease.
Vitamin A is stored in the liver, therefore a daily intake is not essential. Carotenoids are deposited widely throughout the body and can be identified in adipose (fat) tissue, the adrenals and liver. FUNCTIONS OF VITAMIN A
As everyone knows, vitamin A is essential for night vision, but it has many other uses, all of which are vital for the proper health of your body. It is used for growth and maintenance of epithelial tissues which include the cornea of the eye, all mucous membranes, and the linings of the GI tract, lungs, vagina, urinary system, and skin.
It is contributory in the prevention of infectious diseases due to its maintenance of the epithelial tissues (the lining of the lungs, throat, and mouth) in particular. The vitamin prevents tissue wastage from keratinization which can lead to bacterial infection. A also plays an important role in maintaining the immune system functions, specifically in T-lymphocytes and phagocytosis.
To round out its functions, A is active in the growth, formation, and shaping or endochondral tissue of long bones, the spacing of your teeth, and the production of tooth enamel. To top off its values, vitamin A is needed for reproductive function in humans.
DEFICIENCY SYMPTOMS
A deficiency of vitamin A may be caused by an inadequate intake due, in part, by malabsorption diseases that interfere with fat absorption. Symptoms of such maladies are first noticed as changes in the skin, teeth, eyes, and vision.
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