About Vitamin A – Chemistry, Absorption, Utilization and Storage

Presentation Notes on Vitamin A Chemical Composition, Absorption, Storage & Utilisation in Human Body for Students & Kids in word/ .ppt/ .doc Format


Vitamin A is a pale yellow, almost colorless compound soluble in fat or fat solvents and insoluble in water. Because of its high degree of unsaturation, the vitamin A content of fats and oils can be destroyed by oxidation as the fats and oils become rancid. Protection by antioxidants such as vitamin E or storage in a cool, dark place will prevent the oxidation and rancidity.

The vitamin A found in animal foods has two slightly different forms, vitamin A1 and vitamin A2. Vitamin A1 is found chiefly in the liver and body fat of fish and in other foods of animal origin such as liver, milk, butter, and egg yolk. Vitamin A2 which is of little importance in human nutrition, is found in fresh-water fish.
For humans, beta-carotene is the most important because it has the highest vitamin A activity and is the most plentiful.

Absorption, Utilization and Storage : The fat-soluble enzymes vit. A, D, E and K, can all be absorbed via the micellar system with other lipids. The presence of fat, bile salts, and pancreatic juices is essential for complete absorption of natural vitamin A. Esters of vitamin A are hydrolyzed in the small intestine, and retinol passes through the mucosa to be re-esterified. They finally enter the portal blood via a special retinol-binding protein.

The absorption of any of lipid-soluble vitamins can be diminished by the ingestion of mineral oil or any other non-absorbable lipid or any impairment in lipid absorption sequence.
The liver stores the reserves of vitamin A in sufficient quantities to meet the nutritional needs of the individual for many months. Thus the signs and symptoms of vitamin A deficiency develop very slowly. However, in a patient with cirrhosis of the liver, the stores of this vitamin are markedly reduced.

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