an organic substance found in foods and essential in small quantities for growth, health, and the preservation of life itself. The body needs vitamins just as it requires other food constituents such as proteins, fats, carbohydrates, minerals, and water. The absence of one or more vitamins from the diet, or poor absorption of vitamins, can cause deficiency diseases such as rickets, scurvy
, and beriberi
. Vitamins serve as coenzymes or cofactors in enzymatic reactions. They are required only in trace quantities because they are not consumed in the reactions. The major vitamins are designated by the letters A, C, D, E, and K, and the term B complex. The B vitamins and vitamin C are water soluble. The rest are fat soluble and are not absorbed unless the body's digestion and absorption of fats is normal. Deficiencies of the fat-soluble vitamins can be produced by various malabsorption syndromes.
Vitamin A. Vitamin A helps to maintain epithelial tissues which cover the body and line certain internal organs. This vitamin also is essential for the proper growth of skeletal and soft tissues, and is necessary for light-sensitive pigments in the eye that make night vision possible. The particular manifestation of vitamin A deficiency depends upon the age of the patient. Among the most common symptoms of vitamin A deficiency is night blindness. The skin may also be affected, becoming dry and pimply like a toad's skin.
Vitamin A occurs in nature in two forms: retinol (vitamin A1) and dehydroretinol (vitamin A2). It is manufactured by animals and humans from carotenes found in green leafy and yellow vegetables, including kale, broccoli, spinach, carrots, squash, and sweet potatoes. It is obtained directly by eating animal products such as liver, eggs, whole milk, cream, and cheese. A toxic syndrome (hypervitaminosis A) can result from excessive vitamin intake. It is marked by generalized pruritus, desquamation of the skin, loss of hair, and hyperostoses.
The B Complex
. The original “vitamin B” was found to be a group of vitamins, each differing chemically and each individually important in the body. For convenience, these vitamins are referred to as one group since they are often found together in foods. Deficiency in only one of these vitamins is rare, and the deficiency disease attributed to lack of one vitamin B usually is complicated by deficiencies of the others as well.
Vitamin B1 (Thiamine).
This vitamin is necessary to break down and release energy from carbohydrates. Lack of thiamine can cause loss of appetite, certain types of neuritis, and, in severe cases, beriberi
, which affects the brain, heart, and nerves. The best sources of thiamine are yeasts, ham and certain pork cuts, liver, peanuts, whole-grain and fortified cereals and breads, and milk. The vitamin is easily destroyed by cooking and may also be lost by dissolving in the cooking water. Because the body does not store thiamine well, foods that are good sources of it should be included in each day's diet.
Vitamin B2 (Riboflavin).
This vitamin functions as a coenzyme concerned with oxidative processes. Riboflavin deficiency (ariboflavinosis
) was at one time a common vitamin deficiency disease in the United States. It still occurs in parts of Asia, the West Indies, and elsewhere. Symptoms include open sores at the corners of the mouth and on the lips, a purple-red, inflamed tongue, seborrheic dermatitis, and corneal and other eye changes. The main food sources of riboflavin are milk, liver, kidney, heart, green vegetables, dried yeasts, and enriched breads and cereals. It is not usually affected by cooking, but is destroyed by light.
Niacin (Nicotinic Acid).
This B vitamin appears to act in enzyme systems to utilize carbohydrates, fats, and amino acids. Niacin deficiency causes pellagra
, once a major deficiency disease in the United States. Symptoms of pellagra involve the skin and digestive and nervous systems. Niacin also has vasodilating activity. Food sources of niacin are various high-protein foods such as liver, yeast, bran, peanuts, lean meats, fish, and poultry.
Vitamin B12 (Cyanocobalamin).
This vitamin contains cobalt
and is needed for the efficient production of blood cells and for the health of the nervous system. Only small amounts of B12
are required by the body. The activity of this vitamin is associated with that of another B vitamin, folic acid. Inability to absorb vitamin B12
occurs in pernicious anemia
, in which a substance normally secreted by the stomach, called intrinsic factor, is missing. Intrinsic factor is needed to absorb vitamin B12
in the small intestine. Injections of vitamin B12
can control pernicious anemia. Poor absorption of vitamin B12
also occurs in sprue.
is not found in plant foods. The main sources in the human diet are animal products such as milk, eggs, and liver. Probably the ultimate source of B12
is bacterial production in animal intestines. This production occurs in humans, and in normal persons probably meets some or perhaps all of the body's requirements.
Other Members of the B Vitamin Complex.
These include vitamin B6
), biotin, folic acid, pantothenic acid, choline, inositol
, and p-aminobenzoic acid
. Vitamin B6
deficiency can cause convulsions, lethargy, mental changes and retardation, inflammation of the skin, and anemia. These substances, like most other members of the B complex, are widely found in fruits, vegetables, meat, and whole-grain cereals.
Vitamin C (Ascorbic Acid)
. This vitamin is necessary for the health of supporting tissues such as bone, cartilage, and connective tissue. Deficiency produces scurvy
. Vitamin C is found in fresh fruits and vegetables, including citrus fruits, tomatoes, brussels sprouts, and to some extent whole potatoes. Cooking and storage destroy much of the vitamin C content of foods.
. The action of sunlight on the skin changes certain substances in the body into vitamin D, a term for any of several active substances required for the utilization of calcium and phosphorus, which are essential for the growth and maintenance of bone. These include cholecalciferol and ergocalciferol (known collectively as calciferol). Vitamin D deficiency causes rickets
in children and osteomalacia
in adults. Rickets is usually caused either by a diet deficient in vitamin D or by insufficient exposure to sunlight. Few foods contain vitamin D. The only rich natural sources are fish liver oil and the livers of animals feeding on fish. For this reason vitamin D often is added to milk. A toxic syndrome (hypervitaminosis D) can result from excessive vitamin D intake. It results in hypercalcemia with its typical symptoms of weakness, fatigue, loss of weight, and impairment of renal function.
. There are at least eight different antioxidants in this group, of which alphatocopherol
is the most common; they prevent the oxidation of unsaturated fatty acids
, thus preventing cell damage that can lead to neurological symptoms. Because of its ubiquitous nature, supplemental intake of vitamin E is not necessary. It is found in wheat germ oil, cereals, egg yolk, and beef liver.
Vitamin K. Any of a group of vitamins including vitamin K1 (phytonadione) and vitamin K2 (menaquinone) found in alfalfa, spinach, cabbage, putrefied fish meal, and hempseed, which promote blood clotting by increasing the synthesis of prothrombin by the liver; therefore, deficiency of vitamin K delays clotting. Symptoms of vitamin K deficiency are excessive bleeding and bruises under the skin. Generally, the bacteria of the intestine produce vitamin K in quantities that are adequate (provided it can be absorbed), except in newborn infants, in whom the deficiency is most frequently found.
Vitamin Supplements. The exact vitamin requirements for good health often are not known with accuracy; they vary with age, weight, sex, and state of health. The need for certain vitamins increases with fever, some diseases, heavy exercise, pregnancy, and nursing. Persons eating an adequate, varied diet of meats, fruits and vegetables, and dairy products will receive enough vitamins to meet normal requirements. Public health measures such as the addition of vitamin D to milk and the B vitamins to bread and other cereal products have helped to combat deficiency diseases.
The use of vitamin supplements is expensive and in general unnecessary. Specialists in nutrition advise against taking supplementary vitamins unless they are prescribed for a specific reason. Overdoses of vitamins D, A, or K may result in serious disease, with the excess vitamins acting like poisons. Vitamins are commonly prescribed in infancy and childhood, during pregnancy and nursing, for elderly patients whose dietary habits are poor, and in clearly diagnosed deficiency states. These include not only the more familiar deficiency diseases already described but also alcoholism and chronic wasting diseases.