Alice Varney, age 13, of Johnson City, Tenn., for her question:
WHAT EXACTLY IS A VITAMIN?
A vitamin is any of the organic compounds required in minute quantities from the diet for the body to metabolize foods. Vitamins also assist in such other vital body functions as the formation of hormones, blood cells, nervous system chemicals and genetic material
Vitamins generally act as catalysts, combining with proteins to create metabolically active enzymes that in turn produce hundreds of important chemical reactions throughout the body. Without vitamins, many of these reactions would slow down or cease. The intricate ways in which vitamins act on the body, however, are still far from clear.
The 13 well defined vitamins are classified according to their ability to be absorbed in fat or water. The fat soluble vitamins ¬A, D, E and K are generally consumed along with fat containing foods and because they can be stored in the body's fat, they do not have to be consumed every day.
The water soluble vitamins the eight B vitamins and vitamin C cannot be stored and must be consumed every day, with the exception of some B vitamins.
Of these 13 vitamins, the body can manufacture only vitamin D. All the others must be derived from the diet. Lack of them causes a wide range of metabolic dysfunctions.
A well balanced diet contains all the necessary vitamins and most individuals who follow such a diet can correct any previous vitamin deficiencies. Doctors nevertheless have to prescribe vitamin supplements in some cases.
Vitamin supplements are often popularly believed to offer "cures" for many diseases, from colds to cancer, but in fact the body quickly eliminates most of these expensive over the counter preparations without absorbing them. Therefore, it is best to discuss the need for supplements with your family doctor.
A well nourished adult stores enough vitamin A in his liver to meet all his requirements for a year.
The source of vitamin A is carotene, a yellow pigment found in carrots, turnips, yellow corn, green vegetables, liver and fish.
Vitamin D is known as the sunshine vitamin because it is formed in the skin by exposure to sunlight. The ultraviolet rays from the sun, acting on a chemical substance in the skin, convert it to the vitamin. Most foods contain little vitamin D.
Sources of vitamin E are yellow vegetables, especially those containing carotene. Vitamin K is found particularly in green vegetables. Good sources for the B vitamins are whole grain or enriched cereal products, meat and liver. Rich food sources of vitamin C are citrus fruits, tomatoes, green peppers, potatoes and cabbage.