Vitamins are organic compounds found in foods that are necessary in human and animal diets to sustain life and health. There are thirteen vitamins that have been identified as necessary for human health, and several other vitamin-like substances also contribute to good nutrition. The vitamins are named by letters--vitamin A, vitamin C, D, E, K, and eight B vitamins. Because the B vitamins were originally thought to be one vitamin, they were first differentiated by numeral subscripts. Currently B6 and B12 retain the numeric names, and the rest of the B group vitamins are thiamine, riboflavin, niacin, pantothenic acid, biotin, and folic acid.
The discovery of vitamins was a patchwork affair, taking many scientists in distant communities years to piece together the story of the vitaminsÕ role in nutrition. Many of the discoveries of vitamins came from doctors working on the cure of diseases such as rickets, scurvy and pellagra, which are now known to be caused by vitamin deficiency. Scurvy was a disease that particularly affected sailors on long voyages. A Scottish doctor, James Lind (1716-1794), found in 1747 that he could cure afflicted sailors by feeding them citrus fruits. Lind attempted to convince the British navy to change the standard sailorÕs diet to include citrus, but the navy took no action until forced to by a mutiny in1795, a year after LindÕs death. And more than a hundred years passed before it was understood that the vitamin C in citrus was responsible for curing scurvy, a vitamin-deficiency disease. The most exact theory of nutrition in the 19th century came from the English physician William Prout, who laid out the three essentials of the human diet in 1827 as Òthe oily, the saccharin, and the albuminous.Ó The modern-day terms for these substances are fats and oils, carbohydrates, and proteins. Until the early years of the 20th century, ProutÕs work was taken as the last word in nutrition. An English biochemist, Frederick Hopkins (1861-1947) and the Dutch physician Christiaan Eijkman (1858-1930) were instrumental in showing that something besides fats, carbohydrate and protein needed to be part of human and animal diets.
Eijkman worked in the Dutch East Indies beginning in 1886, studying the disease beriberi. PasteurÕs germ theory of disease had just gained acceptance, and Eijkman and his team tried to discover the infectious agent in beriberi. Eijkman found that he could give the disease to chickens by feeding them polished rice, and cure them by giving them brown rice. He correctly surmised that beriberi was caused by a dietary deficiency of some element of rice husk. Hopkins, working in the first years of the 20th century, found that laboratory mice could be made ill if deprived of the amino acid tryptophan. He articulated the theory that there were necessary trace substances in foods, and suggested that rickets and scurvy might be caused by lack of these essential ingredients. These essential substances were named ÒvitaminesÓ in 1912 by a Polish-American biochemist Casimir Funk (1884-1967). Funk thought that all the various essential substances were amines, but when this turned out not to be true, the term was modified to simply vitamins. Eijkman and Hopkins shared a Nobel prize in 1929 for their early apprehension of the vitamin concept.
Research on vitamins proceeded quickly in the first decades of the 20th century. Austrian-American physician Joseph Goldberger (1874-1929) affirmed pellagra as a vitamin deficiency disease, and the American biochemist Conrad Elvehjem (1901-1962), working at the University of Wisconsin, discovered in 1937 that niacin was the missing vitamin in this case. Another University of Wisconsin biochemist, Elmer McCollum (1879-1967), discovered that one vitamin was present in some fats, whereas EijkmanÕs anti-beriberi substance was water-soluble. This meant that they had to be quite chemically different substances. McCollum isolated the first of the named vitamins, vitamin A and vitamin B, and contributed to the discovery of vitamins D and E as well. Studies with animals on vitamin-supplemented diets later showed that something was missing from vitamin B, and the further B vitamins were discovered at various laboratories, with the last one isolated in 1948.
LindÕs work had shown that some substance in citrus fruits prevented scurvy, and this was known as the antiscorbutic factor. But the factor was not isolated until 1928. The chemist Albert Szent-Györgi, working in Frederick HopkinsÕ laboratory, isolated what he at first called hexuronic acid in that year, and was able to prepare large quantities of it from Hungarian red peppers. Studies of Szent-GyörgiÕs acid, which he re-named ascorbic (anti-scurvy) acid led several laboratories to come up with syntheses of it. This was vitamin C. By the late 1930s, cheap synthetic vitamin C was widely available.
Vitamin DÕs discovery is related to research into rickets, a bone-softening disease that affects humans and animals. The folk cure for it was exposure to sunlight. In the 1920s Harry Steenbock, another University of Wisconsin chemist, discovered that an anti-rickets factor could be added to foods by submitting them to ultraviolet radiation. SteenbockÕs process was patented for the enrichment of milk, and English and German researchers finally elucidated the structure of the substance, vitamin D, in the 1930s.
Vitamin E was isolated from wheat germ oil in 1936. Vitamin K, necessary for the coagulation of blood, was first discovered by a Danish scientist in 1929. Scientists at four different laboratories in the U.S. and in Zurich finally isolated vitamin K ten years later. Nutritionists in the 1930s and 1940s also discovered other substances essential for human and animal health, such as sodium, potassium, magnesium, iron and zinc. Research into the known vitamins was essentially complete by 1956, when the complicated structure of vitamin B 12 was finally determined. Vitamin research since that time has focused on the ways vitamins work in the body, and their role in fighting specific diseases. Vitamin research is still one of the most vibrant fields in medicine, as new studies suggest many complex and little-understood functions of vitamins in regulating human health.
This is the complete article, containing 985 words
(approx. 3 pages at 300 words per page).
