Vitamin A, also known as beta-carotene or retinol,
is a very important vitamin. Preformed vitamin A, as is found in fish liver oil, was the first vitamin officially named and was thereby given the letter A to identify it. Retinol, another name for preformed vitamin A, was so named because of its importance in vision. The rods of the eye, which are located within the retina, contain rhodopsin, or visual purple, and need vitamin A for proper vision. Several carotene pigments found in foods, mainly yellow and orange vegetables and fruits, can be converted to vitamin A in our body and thus are termed provitamin A. Beta-carotene is the most available and also the one that yields the highest amount of A.
Vitamin A is absorbed primarily from the small intestine. Absorption of this fat-soluble vitamin is reduced with alcohol use, with vitamin E deficiency, with cortisone medication, and with excessive iron intake or the use of mineral oil, as well as with exercise. As a fat-soluble vitamin, vitamin A can be stored in the body and used when there is decreased intake. About 90 percent of the storable vitamin A is in the liver; it is also stored in the kidneys, lungs, eyes, and the fat tissue. In addition to reducing absorption, alcohol use also depletes liver stores. The storage of vitamin A is decreased during times of stress or illness unless intake is increased. The body needs the mineral zinc to help release stores of vitamin A for use.
Vitamin A is needed at a level of at least 5,000 IUs (international units) per day, though this may vary due to many factors. Deficiencies of vitamin A are still fairly common worldwide and cause many difficulties. Actually, analysis of the average American diet reveals that it provides only about 4,000 units of vitamin A daily, so the many problems of vitamin A deficiency, such as visual changes, skin dryness, and increased infections, are more common than most people realize.
Leafy and Green Vegetables