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Vitamin A
Vitamin A is required by all children for proper growth, and by human beings of all ages for the maintenance of the proper condition of the epithelial tissues, as in respiratory, digestive, and urinary tracts and in glands of internal secretion. It is also necessary for proper formation of the teeth. Another function of this vitamin is its association with the ability of a person to adjust his sight when going from a brightly lighted place to a dark or dimly lighted one. It is essential for the regeneration of visual purple in the eye, a phototropic substance in the retina which is very sensitive to light. Vitamin A is associated with the presence or absence of the deficiency disease known as night blindness or the inability to see well after dark, but not all cases of night blindness are associated with vitamin A deficiency.
There is a popular belief that vitamin A prevents infection such as colds. From the present medical point of view, however, this is not true in its strictest sense, although a deficiency in vitamin A unquestionably lowers the resistance of the body cells and may thereby be related in some measure to the ability to withstand infection. If the body has a good store of vitamin A, and the foods which one eats supply liberal amounts of this vitamin daily, an additional amount of the vitamin will not produce further increases in resistance to infection, as is believed in some quarters.
< align="left"> When animals, including human beings, are deprived in large part of vitamin A, they cannot grow or rebuild worn-out bodily tissues. Such delicate organs as the eyes, when deprived of this vitamin, may likewise become affected by infection. In extremely acute stages of vitamin A deficiency, xerophthalmia, a serious eye disease which may cause complete and permanent blindness if not arrested, is found in rare instances.
Rich food sources of vitamin A are liver, butter, cream, eggs, some kinds of cheese, fish liver oils, some fruits, and some vegetables, especially the green leafy and the yellow vegetables. |