Vitamins - Life prolonging foods

Vitamin A (RETINOL)

In 1912 Hopkins reported normal and continued growth with whole milk and this study led to the discovery of this vitamin by McCollum. It was only in 1913 that Vitamin A was the first Vitamin recognized. It is considered as anti-infective Vitamin responsible for fighting disease. It include A-1 and A-2. Vitamin A-2 has slightly different chemical structure with one more double-bond, but functionally almost similar to A-1. The potency of A-2 is 40% that of A-1. Vitamin A-1 can be derived from B-carotene. Vitamin A exists in several isomeric forms and the most occurring form is the all terms isomer. Retinene (Retinal) is the aldehyde form of Vitamin A.

It is a fat soluble Vitamin and an essential nutrient for growth and survival. In its natural from it is found in animal fats. Vitamin A constitutes a family of compounds generally known as retinols. They have a critical role in vision, cell different and maintenance of epithelial cell integrity. The two active metabolites are retinal, the active element of visual pigment and retinoic acid, and intracellular messenger that modulates cells differentiation. After absorption Vitamin A is stored in the liver as retinal palminate. The liver releases it to circulation bound to Retinol Binding Protein (RBP). Renal disease impairs RBP excretion and increases its concentration in the circulation. The net delivery of vitamin A to the tissues is controlled by the plasma of RBP.

Vitamin A occurs in two hours. The important one for human nutrition is Retinol which is available in crystalline form. It is found in foods of animal origin. As a concentrated solution, retinol is light yellow in colour with mild pleasant odour and gets solidified on cooling. It is soluble in most organic solvents and is insoluble in water. It gets oxidized by air in presence of light.

The other one of Carotene which is a yellow pigment found in vegetahle foods. These Carotenes are precursors of Vitamin A which get converted into Vitamin A have the highest Vitamin A activity. The Carotones are converted into retinol family in the walls of the small intestine. Beta Carotene is considered the wonder food because it has an independent and important role as a powerful antioxidant. In counteracts the effects of free radicals which are responsible for aging, various aged related disorders and Cancer. Beta Carotene can be converted to Vitamin A by a dioxygenase present in the intestine. Beta Carotene is cleaved in the intestinal mucosal cells to yield two molecules of retinol which is reduced to retinol. They are absorbed in the ileum but transported as nonpolar lipids.

About 80% of Vitamin A is absorbed in our system and rest is excreted into faeces within 1 or 2 days. The absorption increases if taken with fat, and gets reduced in cases of jaundice, diarrhoea and abdominal disorders. The absorption is faster in men as compared to women. Out of this absorbed Vitamin A, about half gets combined or burnt down and is excreted in the faeces or urine in a week, and other half gets stored in the liver. A normal person could store about 100 mcg of Vitamin A per gram of liver, or say 1, 50,000 mcg (150 mgs) in an average liver weighing, 1, 500 gms.

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