Vitamins and minerals
Vitamins are carbon-containing substances that are required for normal metabolism but are not synthesized in the body. They are obtained, therefore, from such outside sources as food and water or are administered orally or intravenously. Exceptions to this definition include vitamin D, which is synthesized in the body to a limited extent, and vitamins B12 and K, which are synthesized by bacterial flora in the intestinal tract. Minerals also must be obtained from outside sources.
Vitamins and minerals function as "cofactors" in the metabolism of products in the body. Most aspects of bodily metabolism proceed with the aid of specific enzymes, but if additional catalysts were not present--for example, the cofactor vitamins and minerals--the reactions would proceed so slowly that they would be ineffective.
RDA
In the United States a Food and Nutrition Board has been established for the purpose of determining vitamin and mineral requirements. This board is composed of distinguished scientists and nutritionists and is under the auspices of the National Academy of Sciences. Since 1940 the board has periodically prepared a brochure listing the "Recommended Dietary Allowances" (RDA) of vitamins and other nutrients, based on existing knowledge.
These allowances are intended as a guide for all persons involved in planning food supplies and in the interpretation of food consumption levels. The RDA figures, however, are estimations based on the present state of knowledge of the needs of most human beings; particular requirements will be less or more, depending on numerous individual factors such as genetics, environmental influences, and presence or absence of disease processes.
Supplements
A diet containing generous amounts of fresh vegetables, fruits, dairy products, and meat assures an adequate intake of vitamins and minerals. Extra vitamin intake is not necessary. Dietary supplements of vitamins are often recommended by physicians when any of the following conditions are present: unusual diets obviously deficient in vitamins (insufficient intake); conditions or diseases causing poor intestinal absorption; and increased tissue requirements that occur in relatively healthy individuals during periods of growth, hard physical work, pregnancy, lactation, and menstruation. Some disorders, including hyperthyroidism, infectious diseases accompanied by fever, and tissue-wasting diseases, also cause increased tissue requirements.
Multivitamin Preparations
Two principal types of multivitamin preparations are available to the public and the medical profession: supplemental, or prophylactic; and therapeutic. Supplemental vitamins contain a range of one-half to one-and-a-half times the RDA requirements except for vitamin D, which should not exceed 400 international units (IU) and vitamin A, which should not exceed 1,000 Retinol equivalents. These multivitamin preparations are designed to help prevent disease and to supplement the diet in cases of unusual stress and other such situations.
Therapeutic multivitamin preparations are prescribed by physicians only for deficiency states and for the nutritional support of severe pathological conditions.
Toxicity
Most of the water-soluble vitamins ingested in excessive amounts are rapidly excreted in the urine and thus rarely cause toxicity. The fat-soluble vitamins, on the other hand, are stored in body fat and are capable of causing severe toxicity when taken in excessive amounts, as in the case of vitamins A and D.
FAT-SOLUBLE VITAMINS
Vitamin A
Vitamin A exists in a variety of forms, including retinol, which is currently considered the most active form. Carotene, a pigment in some plants (see CAROTENOID), can be converted in the human body to vitamin A. Vitamin A is also highly concentrated in fish-liver oils. The normal diet contains adequate amounts of vitamin A, and therefore supplements rarely need to be administered.
Vitamin A has many important functions in the body that relate to membrane integrity, especially of epithelial cells and mucous membranes. It is also essential for bone growth, reproduction, and embryonic development. Vitamin A deficiency has long been known to result in NIGHT BLINDNESS, in which the ability of the eye to see in dim light is impaired.
Hypervitaminosis A, which results from excessive intake over a long period of time, is most common in children. Symptoms consist of irritability, vomiting, loss of appetite, headache, dry skin, and scaling of skin. Intracranial pressure is increased, and characteristic bony changes are demonstrable on X-ray examination. An extremely high plasma level of vitamin A occurs in this disorder.
Vitamin D
The active forms of vitamin D are ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3), both of which arise in the body from ingested precursors by exposure of the skin to ultraviolet light. Vitamin D primarily regulates calcium metabolism by determining the movement of calcium from intestines to blood and from blood to bone. It interacts with PARATHYROID hormone and calcitonin (see HORMONE, ANIMAL) in controlling calcium levels. Thus vitamin D is today more legitimately considered a hormone rather than a vitamin. In tropical countries, where exposure to sunlight is high, vitamin D deficiency is rare. It is much more common in northern regions. Ultraviolet irradiation of food products increases their vitamin D content.
A deficiency of vitamin D results in failure to absorb calcium and phosphorus, causing faulty formation of bone. In children the syndrome is known as RICKETS and is manifested by deformities of the rib cage and skull and by bow legs. Adult rickets, or osteomalacia, is characterized by generalized bone decalcification and, eventually, gross bone deformities. Symptoms of hypervitaminosis D consist of weakness, fatigue, lassitude, headache, nausea, vomiting, and diarrhea. Urinary symptoms occur when calcium deposits build up in the kidneys.
Vitamin E
Vitamin E is chemically known as alpha tocopherol, the most active of a group of tocopherols. It is present in seed oils, especially wheat-germ oil. Few vitamins have been advocated for more diseases than has vitamin E, including such diverse disorders as coronary artery disease, muscular dystrophy, habitual abortion, and schizophrenia. Thus far, vitamin E is considered to have possible value in decreasing the risk of cancer; it has shown little therapeutic value in other diseases. Fortunately, it is relatively nontoxic.
Vitamin K
Vitamin K is essential for synthesis by the liver of several factors necessary for the clotting of blood. Chemically, phylloquinone is the natural plant source of vitamin K, and a synthetic derivative, menadione, is used therapeutically. A wide variety of vegetables, egg yolk, liver, and fish oils contain this vitamin. Deficiency of vitamin K rarely occurs. It is used medically in treating specific deficiencies that occur during anticoagulant therapy, in hemorrhagic disease of the newborn, and in hepatocellular disease.
WATER-SOLUBLE VITAMINS
With the exception of vitamin C (ascorbic acid), water-soluble vitamins belong mainly to what has been termed the B complex of vitamins. The better-known B vitamins are thiamine (B1), riboflavin (B2), niacin (B3), pyridoxine (B6), pantothenic acid, lecithin, choline, inositol, and paraaminobenzoic acid (PABA). Two other members are folic acid and cyanocobalamin (B12). Yeast and liver are natural sources of most of these vitamins.
Thiamine
Thiamine, the first B vitamin to be identified chemically (1926), consists of a complex organic molecule containing a pyrimidine and a thiazole nucleus. In the body it functions as a COENZYME in the form of thiamine pyrophosphate and is important in carbohydrate intermediary metabolism. The symptoms of thiamine deficiency are known as BERIBERI, a syndrome consisting primarily of peripheral neuritis marked by sensory and motor paralysis of the limbs and, finally, heart failure. People of Asia who acquired beriberi as a result of a diet of mainly polished rice could be cured by adding rice polishings, which are high in thiamine. Today, thiamine deficiency results from liver damage and most often occurs in nutritionally deficient alcoholics.
Riboflavin
Riboflavin (B2) is a complex organic ring structure to which the sugar ribose is joined. In the body riboflavin is conjugated by phosphate to yield riboflavin 5'-phosphate (FMN) and by adenine dinucleotide to yield flavin adenine dinucleotide (FAD). Both serve as coenzymes for a wide variety of respiratory proteins (see METABOLISM).
Riboflavin deficiency in humans is characterized by growth failure in children; nerve degradation, particularly of the eyes; sore throat; seborrheic dermatitis of the face and extremities; and anemia. The only established use of riboflavin is in the therapy or prevention of deficiency disease.
Niacin
Two forms of niacin (B3) exist: nicotinic acid and nicotinamide. In the body niacin is present in nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which serve as coenzymes in conjunction with protein in tissue respiration and also as dehydrogenases.
PELLAGRA, caused by niacin deficiency, is characterized by a cutaneous eruption, at first resembling sunburn because it affects the areas of the body exposed to sunlight. The tongue becomes red and swollen, with excessive salivary secretion, and diarrhea occurs along with nausea and vomiting. Later, central-nervous-system symptoms appear with headache, dizziness, insomnia, depression, and even overt psychosis with hallucinations and other mental disturbances.
The only established use of niacin is in the treatment of pellagra. Because nicotinic acid in large doses lowers blood lipids, it has been extensively used in the therapy and prevention of arteriosclerotic vascular disease. Toxicity may occur in the form of liver damage, however, with large doses over a prolonged period.
Pyridoxine
Pyridoxine, or vitamin B6, is a substituted pyridine ring structure that exists in three forms, all of which may be converted in the body to pyridoxal-5-phosphate (PLP), the active coenzyme form. PLP functions in human metabolism in the conversion processes of amino acids, including decarboxylation, transamination, and racemization.
Symptoms of deficiency in humans consist of seborrhealike skin lesions of the face; increased irritability; convulsive seizures, particularly in children; and neuritis resulting in degeneration of peripheral nerves. On the other hand, excessive dosages of vitamin B6 over a period of time can also severely damage the nerves.
Pantothenic Acid
Widely distributed in nature, pantothenic acid was first identified in 1933 as a factor necessary to cure certain skin lesions in chicks. Its role in human nutrition, however, has not been clearly delineated. Biochemically, pantothenic acid is converted to coenzyme A, which serves a vital role for a variety of reactions involving transfer of 2-carbon fragments (acetyl groups). It is also essential for the production of metabolic products crucial to all living organisms. Pantothenic acid has no specific therapeutic indications but is included in multivitamin preparations.
Folic Acid
Chemically, folic acid is pteroylglutamic acid. In the body folic acid is converted to folinic acid (5-formyl-tetrahydrofolic acid), the coenzyme form, which accepts 1-carbon units important in the metabolism of many body compounds. Nucleic acid synthesis cannot take place without the presence of folic acid.
Deficiency in humans results in various anemias (see ANEMIA) and can be produced by antivitamins such as methotrexate, which is used in cancer chemotherapy. Folic acid is present in many common foods--for example, vegetables and liver--but can be destroyed by excessive cooking. Deficiency is relatively rare unless caused by an antivitamin, tropical sprue, or pregnancy. The U.S. Centers for Disease Prevention and Control (CDC) recommend that all women of childbearing age consume 0.4 mg of folic acid daily to reduce the risk of giving birth to an infant with spina bifida or other neural tube defects.
Cyanocobalamin (B12)
Vitamin B12, isolated in 1948, is chemically the most complex of all the vitamins. It has a central ringed structure called a corrin nucleus, linked to an aminopropanol esterified by a nucleotide, and also an atom of cobalt to which is attached a cyanide group. Few vitamins are as important metabolically as B12, because it is involved in many of the synthetic steps required in the manufacture of nucleoproteins and proteins. Almost all organisms need this vitamin but only in very small amounts. Vitamin B12 is present mainly in the liver, the kidneys, and the heart. In nature the source is believed to be solely synthesized by microorganisms.
The ability to absorb this vitamin depends on the production by the stomach of an intrinsic factor, a glycoprotein. Cases of B12 deficiency often involve patients with defective production of an intrinsic factor. The symptoms of deficiency are identical to the classical syndrome of pernicious anemia: ineffective manufacture of red blood cells; faulty myelin synthesis, leading to a paralyzing neuritis; and a failure to maintain the epithelium of the intestinal tract. Marked anemia and generalized debility, which eventually develop, are always fatal unless treated. Cyanocobalamin has only one established use, the treatment of this deficiency disease, but is included nevertheless in many multivitamin preparations.
Ascorbic Acid (Vitamin C)
Probably the first deficiency disease to be recognized was SCURVY, and as early as 1720 fresh vegetables or fruit were found to cure the disease. James Lind, a physician in the British navy, demonstrated in 1757 that consumption of oranges and lemons could prevent the disease. As a result of his work and the scurvy-free voyages of Captain James COOK, who adopted his principles, the British navy in 1804 made it compulsory to issue a ration of lemons or limes to sailors, who were from then on nicknamed "limeys." Chemically, ascorbic acid is a plant sugar in the acid form, hexuronic acid. In the body ascorbic acid is reduced to dehydroascorbic acid and is involved in oxidation-reduction reactions. Unlike vitamins of the B complex, it does not act as a cofactor.
The symptoms of scurvy result from the fact that ascorbic acid is essential for the formation and maintenance of intercellular ground substance and collagen. The pathology affects mainly bone and blood vessels; teeth loosen because dentin is absorbed, and the gums become spongy and bleed easily. Hemorrhages in other tissues also occur easily with the slightest trauma. Vitamin C is used to prevent and treat scurvy and many other disorders, including various dental problems. Controversy surrounds the practice of taking very large daily doses of vitamin C to prevent the common cold, because medical research has not supported this notion. Intake of very large amounts for long periods of time can also be harmful, even though vitamin C has a relatively low toxicity. A sufficient daily intake of fresh orange juice provides enough vitamin C for most purposes.
Biotin, Choline, and Inositol
Biotin, a complex organic acid containing sulfur, is a coenzyme for several carboxylation reactions involving carbon dioxide fixation. It is synthesized by intestinal bacteria and is widespread in food products. A natural deficiency in humans is unknown, even in individuals on extremely deficient diets.
Choline, a simple amino alcohol, is a component of lecithin and of acetylcholine, the latter of which is one of the most important neurotransmitters. Unlike most vitamins, choline can be synthesized in the body, provided that methionine intake is sufficient. It is present in large amounts in egg yolk, milk, and seafood. Human deficiency rarely occurs.
Inositol is an isomer of glucose, the common sugar of human diets. It is a component of certain phospholipids. No coenzyme function has been established, but inositol promotes the growth of yeast.
Vitamins and Cancer
There is a growing body of both human-epidemiological and animal-experimental evidence that an adequate intake of vitamins, especially A, C, and E, will lessen the risk of cancer. A prevailing theory is that oxidizing radicals build up in tissues causing degenerative changes in DNA resulting in gene expression of a cancer-promoting nature. Vitamins C and E are ANTIOXIDANTS and help to clear the tissues of these toxic radicals. The mineral selenium in conjunction with vitamin E is essential in this function. Vitamin A is protective of epithelial tissue and is especially important in smokers who tend to be deficient in this vitamin and who are prone to lung cancer.
MINERALS
Unlike sodium and potassium, which are staple elements of the diet and are present in ample amounts in all food of vegetable and animal origin, certain minerals are additional dietary requirements. Although most are present in the average diet, these minerals may not always be ingested in quantities sufficient to satisfy metabolic needs, especially during growth, stress, trauma, and blood loss, and in some diseases.
Calcium
The body's requirements for calcium are generally met by eating or drinking dairy products, especially milk. Most calcium (90 percent) is stored in bone, with a constant exchange occurring among blood, tissue, and bone. The intake is balanced by losses in urine and feces. The blood levels of calcium and its intestinal absorption, deposition, or mobilization from bone are all controlled by a complex interplay of vitamin D, parathyroid hormone, and calcitonin. Contrary to some long-held beliefs, high intakes of protein and phosphorus do not lead to a loss of calcium. Excessive dietary fiber, however, can hinder its absorption (see NUTRITION, HUMAN).
Calcium promotes bone rigidity and is important in maintaining the integrity of intracellular cement and cellular membranes. It also regulates nervous excitability and muscle contraction and may be protective against high blood pressure. During periods of growth, pregnancy, and lactation, calcium intake should be increased. Diseases of calcium metabolism include vitamin D deficiency, hypervitaminosis D, hypo- and hyperparathyroidism, and some forms of renal disease.
Phosphorus
Phosphorus plays an important role in the hemostasis of calcium and in reactions involving carbohydrates, lipids, and proteins. The chemical energy of the body is stored in "high energy phosphate" compounds.
Elemental phosphorus is extremely poisonous, but phosphorus ingested as phosphates in the diet is not toxic.
Iodine
The one important function of iodine is associated with the synthesis of thyroxine and the function of the thyroid gland. Persons living in coastal regions usually receive an adequate supply of iodine because of the high content in seafood. In geographic regions located far inland, however, a lack of iodine in food is apt to occur, causing goiter, so a small amount of iodine is often added by manufacturers of table salt (iodized salt). Elemental iodine is highly poisonous, and its only use in medicine is as an antiseptic.
Iron
Iron is a vital component of hemoglobin and also of certain respiratory enzymes. Foods high in iron content include meat (liver and heart), egg yolk, wheat germ, and most green vegetables. Increased requirements for iron occur during the growth period and pregnancy and with excessive menses and other instances of blood loss. The average diet contains 10 to 15 mg a day, adequate for most people. Iron deficiency, resulting in anemia, can be treated by large amounts of iron in order to gain positive absorption.
Magnesium
Magnesium is an essential element in human metabolism and functions in the activities of muscles and nerves, protein synthesis, and many other reactions. Magnesium deficiency may occur in alcoholism, diabetes mellitus, pancreatitis, and renal diseases. Prolonged deficiency can cause changes in heart and skeletal muscle. Excessive retention of magnesium can occur in renal disease and results in muscle weakness and hypertension.
Zinc
Zinc serves as a cofactor of dehydrogenases and carbonic anhydrase; its lack can cause skin rashes, taste disturbances, and mental lethargy. Zinc loss occurs during such stress situations as surgical operations, and its replacement aids in wound healing. Dietary programs often promote zinc loss, and the use of concentrated zinc supplements can lead to calcium deficiency. Overingestion of zinc or inhalation of its vapors can cause depression, vomiting, and headache.
Fluorine and Trace Minerals
Fluorine as fluoride is a requirement to bind calcium in bones. Microamounts of such elements as boron, chromium, chlorine, copper, manganese, molybdenum, selenium, silicon, sulfur, and vanadium are considered necessary to health. Copper deficiency, for example, has been linked with heart disease, and the onset of diabetes in older age may in some way be associated with chromium deficiency. Normal diets appear to provide adequate amounts of trace minerals, but effects such as the linking of high levels of fructose in the diet with copper-deficiency problems are the subject of ongoing research.
Joseph R. DiPalma, M.D.
Bibliography: Bender, D. A., Nutritional Biochemistry of the Vitamins (1992); Centers for Disease Prevention and Control, "Recommendations for the Use of Folic Acid to Reduce the Number of Cases of Spina Bifida and Other Neural Tube Defects," Morbidity and Mortality Weekly Report, September 1992; Combs, G. F., Jr., The Vitamins (1991); Consumer Guide, Complete Book of Vitamins and Minerals (1988); DiPalma, J. R., and Thayer, W. S., "Use of Niacin as a Drug," Annual Review of Nutrition 1991; Griffith, E. W., ed., Vitamins, Minerals, and Supplements (1988); Jacobs, M. M., Vitamins and Minerals in the Prevention and Treatment of Cancer (1991); Shils, M. E., and Young, V. R., eds., Modern Nutrition in Health and Disease (1988).
nutritional-deficiency diseases
Nutritional-deficiency diseases result primarily from a diet that does not have enough of the nutrients that are essential to health or development (see DIET, HUMAN). Another cause is that an individual may not be able to utilize properly the nutrients consumed in the diet. Deficiency diseases may result from a person's abnormally high metabolic needs for a nutrient or from some imbalance in the nutrients ingested. Certain drugs or medicines may also affect the utilization of nutrients.
Symptoms of many of these disorders include severe weight loss. The greatest tissue loss can occur in the intestines and liver. Most systems are affected, including the body's immune system. The skin appears dry and pale; the hair is dry and sparse and may fall out. Respiratory rate and heart output are reduced. Endocrine disturbances result in AMENORRHEA in women. DIARRHEA frequently occurs in undernourished individuals and can result in death.
Nutrient deficiencies produce a wide variety of illnesses; in fact, nutritional deficiency contributes to much of the ill health in developing countries. In these countries the most important forms of malnutrition are protein-calorie malnutrition (PCM); endemic GOITER and cretinism because of iodine deficiency; vitamin A deficiency leading to xerophthalmia (abnormal dryness of the eye), which may impair vision; and nutritional ANEMIAS.
DEFICIENCY DISEASES
Humans obtain energy (measured in calories or joules) from carbohydrates, fat, and protein and also from alcohol. In the majority of societies the most available source of calories is carbohydrate, and fat and protein are less available. In general, as families or communities become more affluent, the proportion of fat and animal protein in the diet increases.
Protein-Calorie Malnutrition
A failure to consume adequate quantities of food energy may lead to loss of weight or growth failure in children, wasting of tissues, and eventually STARVATION. The production of enzymes and hormones is impaired in severe protein deficiency. Young children living in poorer communities throughout the world commonly have protein-calorie malnutrition. This condition is aggravated by common infections, such as diarrhea, and sometimes by the irregular intervals at which a child may have food to eat.
The two clinical forms of PCM are nutritional MARASMUS and KWASHIORKOR. Marasmus is due primarily to an energy (calorie) deficiency; in kwashiorkor, protein deficiency predominates. Mild or moderate PCM is much more common than these two severe forms and leads to a slow rate of growth, to poor development, to increased susceptibility to infections, and eventually to permanent physical stunting.
Mineral Deficiency
Other nutritional-deficiency diseases include those due to mineral deficiencies and those due to vitamin deficiencies. The most important simple mineral deficiencies are iron deficiency, a common cause of ANEMIA; iodine deficiency, leading to goiter and sometimes cretinism; and fluoride deficiency, which contributes to tooth decay.
Vitamin Deficiency
The major vitamin-deficiency diseases include xerophthalmia, which is due to vitamin A deficiency. It can result in ulceration of the cornea of the eye and increased susceptibility to infection and sometimes blindness. BERIBERI, a thiamine, or vitamin B-1, deficiency, is commonly found among rice-eating peoples and alcoholics. Pellagra results from a deficiency in niacin and is associated with persons eating mainly a corn, or maize, diet. A riboflavin, or vitamin B-2, deficiency causes ariboflavinosis, in which there may be cracks of the lips and red, scaly lesions in the genital areas. The macrocytic anemias (involving abnormally large red blood cells) result particularly from folic-acid deficiency during pregnancy and sometimes from B-12 deficiency. RICKETS and osteomalacia (softening of the bones) are due to vitamin D deficiency, and SCURVY is due to vitamin C deficiency. Other vitamin deficiencies, such as vitamin K deficiency in the newborn and vitamin B-6 deficiency in those taking certain medications, are much less important and less prevalent.
Treatment
The specific treatment for each of these deficiency states is usually the medical provision of appropriate doses of the nutrient in question and also an assurance that foods rich in these nutrients are consumed in the diet. This latter approach is also the basis for prevention of these diseases. Some diseases may also be prevented by fortification of commonly eaten foods with nutrients, by various food supplement programs, by increasing local production of nutritious foods, and, in the long run, by better nutrition education.
PROBLEMS OF WORLD HEALTH
In recent years world concern has increased both about hunger and to some extent about malnutrition. In most parts of the world major FAMINES have led to international action to reduce the extent of starvation.
The World Health Organization (WHO), the Food and Agriculture Organization (FAO), and United Nations Children's Fund (UNICEF), all agencies of the United Nations, play important and different roles in trying to reduce the extent and seriousness of malnutrition, particularly in developing countries. They coordinate activities and attempt to establish international standards of classification and reporting; they also make recommendations about nutrient requirements for different population groups. (See also AGRICULTURE AND THE FOOD SUPPLY).
In the United States the Food and Nutrition Board of the National Academy of Sciences/National Research Council publishes Recommended Dietary Allowances (RDA) of all the important nutrients.
Taken From:Michael C. Latham.Bibliography: Chandra, R. K., eds., Nutrition and Immunology (1988); Cornatzer, W.E., Role of Nutrition in Health and Disease (1989); Halstead, C. H., and Rucker, R. K., eds., Nutrition and the Origin of Disease (1988); Hess, A. F., Scurvy: Past and Present (1982); Krause, M. Latham, M. C., Human Nutrition in Tropical Africa, 2d ed. (1980); Rose, John, ed., Nutrition and Killer Diseases (1982); Somogyi, J. C., and Varela, G., eds., Nutritional Deficiencies (1981); Todd, G. P., Nutrition, Health and Disease, ed. by R. S. Friedman (1985); Trowell, H. C., Kwashiorkor (1982); Walker-Smith, J. A., and McNeish, A. S., Diarrhea and Malnutrition in Childhood (1986); Werbach, M.R., Nutritional Influences on Illness (1989); Woodward, J. C., and Bruss, M., eds., Comparative Aspects of Nutritional and Metabolic Diseases (1983).
Vitamins (history)
A new kind of medicine arrived with the discovery of vitamins. Although nutritional deficiency diseases were known since the work of James Lind and others, the different chemical identities of the substances causing the diseases were not discovered until the twentieth century. The term `vitamin' was coined in 1912 by Casimir Funk, a chemist working at the Lister Institute in London. It was partly his research that helped clarify the distinctive functions of vitamins.
When Funk started his work, it was known from clinical studies that certain human diseases were caused by a deficiency of specific vitamins: for example, beriberi for lack of thiamine (vitamin B1) (see Diseases, Nutritional and Medical Breakthroughs, 20th Century); scurvy, long known to be prevented by a sufficiency of citrous fruits, for a lack of ascorbic acid (vitamin C) (see Scurvy, An Early Clinical Trial); and so on.
It was realized that where there was a lack of a particular vitamin in the diet, treatment with that vitamin was life-saving. Once this became known, there were no further doubts about how to treat specific deficiency diseases.
Regrettably, however, superstition grew fast about vitamins, and they promptly acquired a reputation as magical cure-alls. Manufacturers were quick to exploit the myth, baffled physicians were relieved to adopt it, and comfort-seeking patients were (and are) all too willing to believe it.
Evidence for minor benefits from various vitamins is hard to obtain and generally of the anecdotal and unconvincing kind. But poisoning by excess, particularly of the fat-soluble vitamins, is well known: nervous disturbances and birth defects are produced by an excess of vitamin A, and excess of body calcium and kidney stones after too much vitamin D.
But vitamins remain a popular and heavily promoted form of therapy, rarely (in prosperous countries) with any rational basis. They are probably more rewarding to the shareholders of manufacturing companies than to most of the people who consume them.
Whether vitamins are drugs is a matter of the use of language, and need not be pursued. The term vitamin, contracted mistakenly by Casimir Funk from `vital amine', is misleading, because most accessory food factors are not amines, and whether they are vital, meaning essential for survival, differs from species to species. But the name has come to stay.
The way vitamins act in living cells throws much light on the ways cells work, and knowledge of this activity has been used to design drugs for specific purposes, especially antibacterial agents. The detailed biochemistry of vitamins was worked out largely in microbes - much more convenient and socially acceptable research subjects than mammals.
From the knowledge so gained it was a simple step (although few saw the great possibilities) to go on to designing antibacterial drugs that interfere with the way microbes use their essential foods. Remarkable results followed.
Taken From: Webster's World Encyclopedia 2000.
