Vitamin A, also called retinol, is most important 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.
In a related role, vitamin A helps maintain the body’s epithelial tissues. These are the skin and the linings of the nose, mouth, and throat, the eyes, ears, and lungs, and the digestive and urinary tracts. Healthy epithelial tissues are smooth and soft, and are 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 smell, 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.
In the United States, overdosage of vitamin A is aserious medical problem. Vitamin A, like all fat-soluble vitamins, can be stored in the body. The question of the minimum human requirement for vitamin A is a cloudy issue because the liver can keep amounts for more than a year.