Category:Vitamins

A vitamin is an organic compound required in small amounts in the diet for normal metabolism, the deficiency of which produces a characteristic disease. The category is fixed in number, thirteen substances in current usage, and conventionally divided into the fat-soluble vitamins (A, D, E, K), absorbed with dietary lipid and stored in adipose tissue and liver, and the water-soluble vitamins (the B-vitamins and vitamin C), absorbed by the small intestine, excreted in the urine, and accumulated only in small body stores.

The clinical recognition that something in food, beyond protein and carbohydrate and fat, was necessary for life is older than the chemical isolation of any of these substances. In May 1747 the Scottish naval surgeon James Lind, aboard HMS Salisbury in the Bay of Biscay, divided twelve scorbutic sailors into six pairs and assigned each pair a different treatment: cider, dilute sulphuric acid, vinegar, sea water, a paste of garlic and mustard and horseradish, or two oranges and a lemon a day. The pair given the citrus fruit were back on duty within a week.^[1] The Royal Navy adopted lemon juice as a routine ration in 1795 and largely eliminated scurvy from the British fleet, although the active principle would not be identified for another one hundred and forty years.

The systematic study of dietary deficiency disease began in the 1880s. The Dutch physician Christiaan Eijkman, working in a military hospital on Java in the Dutch East Indies on the problem of beriberi, observed in 1889 that the chickens of the hospital coop, fed on the polished white rice of the patients' table scraps, developed a polyneuropathy that resolved when they were returned to a diet of unpolished brown rice. He concluded, after some misdirection through a hypothetical bacterial toxin in the polished rice, that the rice husk contained a substance whose absence produced the disease.^[2] A generation later, in 1906, Frederick Gowland Hopkins at Cambridge showed that young rats fed a fully purified diet of protein, fat, carbohydrate, and salts did not grow, but did grow when a small daily amount of milk was added; he postulated, and named, the "accessory food factors" responsible.^[3] In 1912 the Polish biochemist Casimir Funk, working at the Lister Institute in London, isolated from rice polishings an active fraction that cured experimental beriberi in pigeons; believing the substance to be an amine, he proposed the name vitamine, from vita for life. Not all of the substances later included turned out to be amines, and the terminal "e" was dropped; the name remained.

The chemical isolation of the individual vitamins occupied most of the second quarter of the twentieth century. Elmer McCollum and Marguerite Davis at Wisconsin established in 1913 the existence of a fat-soluble factor they called A and a water-soluble factor B; the alphabetic scheme expanded as additional factors were separated. Joseph Goldberger of the U.S. Public Health Service showed between 1914 and 1928 that pellagra, then endemic in the southern United States, was a deficiency disease and not an infection, and Conrad Elvehjem at Wisconsin identified the missing factor as nicotinic acid (niacin) in 1937.^[4] Albert Szent-Györgyi in Szeged isolated hexuronic acid in 1928 and showed it was the antiscorbutic vitamin C in 1932, work for which he received the 1937 Nobel Prize; Tadeus Reichstein in Basel and Walter Haworth in Birmingham independently synthesised it within months. Henrik Dam in Copenhagen identified the anti-haemorrhagic factor vitamin K in 1929, named for the Danish koagulation, and isolated phylloquinone in 1939; Adolf Windaus worked out the sterol structure of vitamin D in 1928, and the Wisconsin biochemist Harry Steenbock showed that ultraviolet irradiation of ergosterol produced vitamin D2 (ergocalciferol), a finding that within a few years eliminated rickets from the industrial north of the United States and Europe. The isolation of cyanocobalamin (vitamin B12) by Karl Folkers at Merck and Lester Smith at Glaxo in 1948, followed by Dorothy Hodgkin's crystallographic determination of its structure at Oxford in 1956, closed the list.

The clinical pharmacology of the vitamins divides cleanly into two kinds of indication. The first is the replacement of a deficient nutrient when the deficiency is documented or when its consequences are anticipated: cyanocobalamin in pernicious anemia, parenteral phytomenadione in warfarin reversal and in haemorrhagic disease of the newborn, folic acid before and during pregnancy for the prevention of neural-tube defects (since 1998 fortified into the U.S. grain supply, with measurable reduction in the prevalence of anencephaly and spina bifida),^[5] and the cholecalciferol and ergocalciferol preparations for the rickets and osteomalacia of vitamin D deficiency, a condition now identified in a substantial fraction of the elderly, dark-skinned, and high-latitude populations of the developed world. The second indication is pharmacological, that is, the use of a vitamin at a dose well above replacement to produce a non-nutritional pharmacologic effect: niacin in gram doses for the dyslipidaemias (its first lipid-lowering effect was reported in 1955), pyridoxine in pyridoxine-responsive seizures and isoniazid neuropathy, the active vitamin D metabolite calcitriol for secondary hyperparathyroidism in chronic kidney disease.

The history of the vitamin includes a substantial volume of work that has not held up. Linus Pauling's advocacy of gram doses of vitamin C for the common cold and for cancer prevention, taken seriously in the 1970s, has not survived randomised trial.^[6] Routine vitamin E supplementation, on the basis of an antioxidant hypothesis for cardiovascular and oncologic prevention, has been associated in some trials with a small but consistent excess of all-cause mortality. The use of high-dose beta-carotene as a chemopreventive in smokers was abandoned after the CARET and ATBC trials reported, in 1996, an increase rather than a decrease in lung cancer in the treated group.^[7] A vitamin is, in the contemporary clinical view, a medicine to be used when there is reason to use it: a quantified deficiency, a population-specific risk, a pharmacological indication beyond replacement. The default of routine multivitamin supplementation in the absence of any of these has not survived its examination.

By solubility, the conventional classification:

• Fat-soluble vitamins (A, D, E, K): retinol and retinyl palmitate; the vitamin D analogues calcitriol, cholecalciferol (D3), ergocalciferol (D2); vitamin E (alpha-tocopherol); phytomenadione (vitamin K1) and menaquinone (K2)
• B-vitamins (water-soluble): thiamine (B1), riboflavin (B2), nicotinic acid (B3) and nicotinamide, pantothenic acid (B5), pyridoxine (B6), biotin (B7), folate / folic acid (B9), cyanocobalamin (B12)
• Water-soluble vitamin C: ascorbic acid

The active hormonal form of vitamin D, calcitriol (1,25-dihydroxycholecalciferol), is a hormone rather than a vitamin in the strict sense; it is listed under both vitamin D analogues and hormones.

The boundary of this category is "medicine consisting of, or directly derived from, a substance recognised as a vitamin in normal human nutrition." Mineral supplements (iron, calcium, magnesium, zinc, selenium) are essential nutrients but are not vitamins and are collected separately, under iron supplements, calcium supplements, and trace elements. The fish-oil concentrates and other omega-3 fatty acid preparations, although often sold alongside multivitamins, are not vitamins and are collected with the lipid-lowering agents when used pharmacologically. Folinic acid (leucovorin), a vitamin-derivative used to rescue patients from methotrexate toxicity and to potentiate fluorouracil, is collected separately under its oncologic indication. Vitamin-deficiency diseases (scurvy, beriberi, pellagra, rickets, the megaloblastic anemias, the haemorrhagic disease of the newborn) are described, briefly, on the corresponding medicine pages.

This category page is an encyclopedia article about its subject. The actual index of medicines belonging to the category is generated automatically by the wiki engine, from category-membership declarations on the individual medicine pages, and appears at the foot of the page below the references.