The first nutritional deficiency disease to be clearly recognized was probably nightblindness. The ancient Egyptians, as mentioned in the Papyrus Ebers and later in London Medical Papyrus, recommended juice extractd from cooked liver to be applied to the eye to cure nightblindness. These observations and writings date even before 1500 B.C. Ancient Greeks have also recommended both ingestion of cooked liver for cure of night blindness. It was however in 1913, that Vitamin A was recognized as the first fat soluble vitamin and essential nutrient for growth and survival of the body. In 1930, it was established that carotene pigment in carrots, fruits and some vegetables is converted to Vitamin A in the body.
Vitamin A or retinol is found in food of animal origin, while carotene is provided by foods of both plant and animal origin. Vitamin A can either be ingested or synthesized within the body from plant carotene.
Approximately 80% of Vitamin A is absorbed in human system. It is passed along with fat through the lymphatic system into the bloodstream. The absorbtion of vitamin A increased if it is taken with fats. Women absorb Vitamin A faster than men. During diarrhea, jaundice and abdominal disorders, Vitamin A absorption is poor. Vitamin A is stored in liver. A healthy person can store about 100 mcg of Vitamin A per gram of liver. Of the Vitamin A absorbed, about 20-50 percent either combines with or burns down into products that are excreted within about one week in the faeces and urine. Remaining 20% of Vitamin A which is not absorbed is extracted within one or two days into the faeces.
Functions of Vitamin A: The best defined function of Vitamin A is its role in vision. It provides the required stimulation for vision in the retina. In addition, Vitamin A is required for growth, reproduction and maintenance of life. It builds up resistance to respiratory and other infections, and ckeeps the mucous linings and membranes of the body, especially those of the eyes, lungs, stomach, and intestines, in healthy condition. It prevents eye diseases. It aids in the secretion of gastric juices, and the digestion of protein. It also plays a vital role in preventing and clearing up infections of the skin and in promoting healthy hair, teeth and gums. Vitamin A increases permeability of blood capillaries and thereby contributing better tissue oxygenation. It also helps prevent premature ageing and senility, increase life expectancy, and extends youthfulness.