VITAMINS. – Regulatory principles, largely known chemically, contained in animal and vegetable tissues used as food. The name “vitamins,” coined by Funk, is the most widespread, though improper because not all these principles contain nitrogen; they have also been called “accessory dietary factors” (McCollum), “eutonins” (Pugliese), “nutramines” (Abderhalden), and “completins” (R. Berg).
I. HISTORY
The history of vitaminology is recent, even though as early as 1720 the Dutch physician Kramer made interesting observations on the relationship between scurvy and diet. Generally, the field is considered to begin with the findings of Lunin (1881) and the Italians Coppola and Pasqualis (1895–96), who suggested that natural foods, such as milk, contained principles necessary for metabolic balance beyond the known classes of foodstuffs. In 1897, Eijkman made fundamental observations on the relationship between a diet consisting exclusively of polished rice (as used in many regions of the Far East) and beriberi; in 1906, Hopkins published exemplary research on the inadequacy of synthetic diets, even when combined with full respect for energy requirements and amino acids. In 1910, Stefani hypothesized that pellagra results from the absence in a poor diet of something “imponderable” yet necessary to the organism. In 1912, Holst and Frølich described the condition of experimental scurvy in guinea pigs, recognizing it as a deficiency of a factor of this kind, found especially in certain vegetable tissues and fresh animal organs but absent in cereal grains; they thus placed on a secure experimental basis the old empirical observations of sailors and explorers. In 1914, Funk published a fundamental monograph on vitamins and their related deficiencies or “avitaminoses.” To complete this outline of the development of vitaminology, after recalling the work of McCollum and Davis, who distinguished vitamins into fat-soluble and water-soluble (1915), it is fitting to add that Lorenzini and collaborators, as early as 1917, had begun studying methods of extracting and stabilizing vitamins and envisaged various therapeutic applications, recognizing the importance of those dysvitaminoses linked to the organism’s inability to use vitamins correctly, even when normally supplied by the diet. Particularly, the study of such dysvitaminoses, along with avitaminoses from imbalance, has been taken up with special interest by the most modern research directions. Nowadays, chemistry has taken hold of vitamin studies, and thanks especially to eminent chemists such as Windaus, Karrer, Szent-Györgyi, Williams, R. Kuhn, and others, synthesis has been achieved for almost all the vitamins now known.There are at least 14 vitamins, but in the syllabus presented by the “Council on Foods and Nutrition” of the American Medical Association (published in June 1946), only the manifestations of seven vitamin-deficiency states are noted—namely, those avitaminoses that have been definitely observed in humans and are of dietary origin. Some of the omitted vitamins have been shown to be essential only under special experimental conditions. Many vitamins, since they are not synthesized by human tissues, are ordinarily produced in sufficient quantity by the bacteria of the intestine. Sulfonamides, for example, which inhibit the growth of intestinal bacteria, can give rise to various forms of avitaminosis.
Today, in evaluating the quantities of vitamins necessary in the diet, there is a tendency to ensure a wide margin of safety to avoid the possible onset of deficiency symptoms under unfavorable conditions. Vitamin-deficiency diseases are often the result of multiple factors, and the lack of vitamins in the diet is only one of their causes, as, for example, in rickets; until a better understanding is reached of the accessory causal factors, generous administration of vitamins is to be recommended as the only sure means of prophylaxis, especially during periods of increased requirement and illness.
Alongside cases of hypovitaminosis from deficient vitamin intake, deficiency states from complete failure of utilization can also be observed; thus, for example, a disorder of intestinal absorption of fats can imply poor absorption of fat-soluble vitamins, even when dietary intake of them is entirely normal. The metabolic imbalance induced by vitamin deficiency can cause irreparable and irreversible lesions: Mouriquand has called “paravitaminosis” the morbid condition represented by lesions resistant to administration of the specific vitamin. It is now established that one deficiency aggravates another, and that an adequate supply of vitamins enables the organism to maintain equilibrium with a lower protein quota.
II. CLASSIFICATION
Vitamins are commonly divided into fat-soluble, i.e., bound to fats, soluble in them and extractable with fat solvents, and water-soluble, i.e., soluble in aqueous media and extractable by water or hydroalcoholic extraction.The most important fat-soluble vitamins are: 1) vitamin A or antixerophthalmic vitamin, contained especially in cod-liver oil, raw spinach, butter, egg yolk, and fresh tomatoes; it is very important for vision, anti-infective action, and epithelial protection; 2) the group of vitamin D or calcifying or antirachitic vitamins, little widespread in nature; cod-liver oil is especially rich in it; for the development of rickets, besides dietary deficiency and lack of solar irradiation of the organism, the calcium-phosphorus balance in the diet also counts; 3) vitamin E or antisterility vitamin, which promotes fertility in animals, is present in cereal embryos, green leaves, nuts, and peas; it also appears to be a neurotropic factor of great importance; 4) vitamin K or antihæmorrhagic vitamin, whose deficiency produces hæmorrhages and reduced blood coagulability: K1, of vegetable origin, is contained especially in green leaves, oats, and wheat; K2, of bacterial origin, is found in the liver, derived from saprogenic intestinal germs; 5) the so-called vitamin F, an unsaturated fatty acid, whose deficiency produces mainly disorders of cutaneous nutrition.
The most important water-soluble vitamins are: numerous factors extractable from yeasts, which constitute the B complex; the multiple factors that make up this complex, distinguishable according to their resistance to heating, are not yet all sufficiently known. The most studied are: 1) vitamin B1 or aneurin or thiamine, an anti-neuritic vitamin of fundamental importance, since around it a complex of indispensable enzymatic functions (decarboxylation, oxidation, phosphorylation) is centered; it promotes alcoholic fermentation and the multiplication of bacteria; as Williams says, it is one of the earliest inventions to evolve life; 2) vitamin B2 or riboflavin or lactoflavin, contained in lactic and butyric bacteria, in egg white, and in milk serum; it is anti-somatitic, anti-eczemic, and perhaps also anti-pellagric; 3) vitamin B3 or adermin or pyridoxine, contained in rice bran, egg yolk, and beef liver; it is anti-dermatitic; 4) vitamin PP, anti-pellagric, nicotinamide, of fundamental importance in the protection of the skin, mucous membranes, and nervous system; it is a constituent of the active group of enzymes involved in oxidation-reduction processes (dehydrogenases); 5) vitamin B12, active in doses of a few gamma (γ = thousandth of a milligram) against pernicious anemia; and finally, 6) folic acid, against pernicious and granulocytic anemias; 7) pantothenic acid; 8) vitamin H or anti-seborrheic or biotin.
Also belonging to the water-soluble vitamins are: 9) vitamin C or ascorbic acid, anti-scorbutic; it is widely distributed in the plant kingdom (especially in peppers, lemons, and asparagus); it cannot be synthesized by man or monkeys, who must therefore obtain preformed ascorbic acid from external sources; the fundamental function of vitamin C is to transport hydrogen in the oxidation-reduction processes of cells; its requirement is increased in fever and in all infectious diseases that require an increase in adrenal protective function; 10) vitamin P or citrin or capillary permeability vitamin, a complex of flavonic substances with a generally anti-hemorrhagic action; its action overlaps only partially with that of ascorbic acid, since it primarily regulates vascular permeability.
All these exogenous regulators, introduced as such or as precursors (provitamins) that the organism can convert into vitamins, are normally involved in fundamental vital processes for all cells. Some vitamins undoubtedly influence the central and peripheral nervous system and perhaps especially the autonomic nervous system; the relationships between certain aspects of dermatology and ophthalmology and vitaminology are also extensive. The relationship between vitamins and natural immunity has been widely studied.
In cases of dietary restrictions imposed for any reason on a community, vitamin deficiency can cause more serious damage than a reduction in caloric intake. Vitamins, which are true plant hormones and often act as growth factors for plants themselves, therefore play a fundamental role in the rational nutrition of modern man (Virtanen) and constitute a vast and important chapter, still developing, of nutritional science.