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Vitamin A, also called retinol, is most significant to the health of our eyes. The retina, that part of the eye which reacts to light, changes when we see colors and light or dark. After each reaction the eye needs vitamin A to restore the retina so we can continue to see. An inadequate supply of vitamin A leads to night blindness, causing the eyes to readjust slowly, making it difficult to see in dim light or when changing from light to dark.
Vitamin A helps maintain the body's epithelial tissues. These are the skin and the linings of the nose, mouth, and throat, the eye, ears, and lungs, and the digestive and urinary tracts. Healthy epithelial tissues are smooth and soft, and resistant to infection.
Normal growth and development of bones during childhood and their continued soundness in the adult years depend on vitamin A. It also plays a part in the reproductive process and in the creation of hormones.
A shortage of this vitamin can have serious consequences. Xerophthalmia, the advanced stage of night blindness that could lead to permanent loss of vision, is widespread in the Third World. Other symptoms of deficiency include hardening and drying of skin, partial loss of the senses of taste and small, increased vulnerability to respiratory infections, and faulty development of bones and teeth in children. Serious deficiencies are almost unheard of in this country, even though one-third of children get less than the Recommended Dietary Allowance level of vitamin A. This is because the RDA for Vitamin A, as for all vitamins, is well above actual daily need to allow for substantial shortage.
Infants, children, and teenagers need more vitamin A than adults to help their developing bones and teeth. However, recommended amounts of the vitamin are based on body weight, and increase from 400 micrograms of retinol equivalents for an average one-year-old child to 1,000 micrograms for teenage boys and 800 for teenage girls. Excess amounts of this vitamin can cause glare blindness, loss of appetite, irritability, loss of hair, headaches, joint pain, and nausea. Prolonged mega dosing can lead to an increase in pressure inside the skull and even to death. Most vitamin A overdoses occur when children are given a high-potency vitamin supplement. No one should take more than the RDA of vitamin A except on the advice of his physician, after proper evaluation by that physician. Anyone taking 25,000 or more units of vitamin A daily should have his blood vitamin-A level measured at regular intervals to determine if the blood vitamin A is rising to toxic levels.
Vitamin A, or retinol, is supplied by animal products such as liver, fish oils, milk, and butter. Primary sources of vitamin A are the carotenoid pigments synthesized by plants, these pigments contain beta-carotene. When taken into body, each molecule of beta-carotene is split, and combining with water, forms two molecules of vitamin A. This process is thought to take place in the liver, where the vitamin is then stored. Eating excessive amounts of vitamin A in any product can be toxic.
Deep-yellow vegetables such as pumpkin, squash, carrots, or yams, and leafy greens such as spinach and broccoli are excellent sources of vitamin A. Cantaloupe, apricots, and mangoes are also high in vitamin A.
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