Vitamins

Although the scientific evaluation of diets at the end of the nineteenth century focused on protein and energy, some realized that there were other requirements for a healthy diet. In particular, it was known that sailors on long voyages developed scurvy unless they periodically ate fresh green vegetables or fruit. Citrus fruit juice was particularly valued. James Lind, a British naval surgeon, carried out a famous controlled trial on a group of scorbutic sailors in 1747. He found that a combination of oranges and lemons produced a rapid cure, whereas neither sulfuric acid nor vinegar had any value.

Lind believed that scurvy resulted from the debilitating effect of the moist air in ships at sea and that the antiscorbutic factor in citrus fruits was not normally needed by people living on land. Nineteenth-century experience showed that this was not so. Scurvy was a serious disease among those rushing to the California gold fields in 1849, both when they were en route by ox wagon and after they had arrived. It caused thousands of deaths in the Allied armies during the Crimean War, and even broke out during the relatively short siege of Paris in 1870-1.

A lecturer at a London medical school had said in 1830: "Scurvy is a purely chemical disease . . . each part of the body is ready to perform all its functions, but one of the external things necessary for its doing so is taken away." He compared the condition to the suffocation of someone deprived of fresh air. The "necessary thing" for preventing scurvy, he said, was contained in fresh animal and vegetable food. By contrast, the diet of sailors and soldiers on active duty was normally restricted to dried and preserved foods. His views were finally to be proved correct 100 years later. After a series of erroneous guesses as to the nature of the antiscorbutic factor, real progress was made when a report from Norway in 1907 indicated that the disease could be reproduced in guinea pigs. This made it practicable to test different fractions of lemon juice and other foods, to concentrate the active factor, and finally to isolate it. This work was completed in 1932, and the chemical, called ascorbic acid (or vitamin C), was synthesized in 1933. Ascorbic acid proved similar to a sugar in its structure, and a daily intake of only 10 milligrams per day was sufficient to prevent scurvy. (This corresponds to approximately one-eighth of an ounce over an entire year.)

Since the discovery of vitamin C, there has been some controversy as to how much is required for optimal health. The official recommendation in most countries is from 30 to 75 milligrams per day, levels that can be provided by an ordinary mixed diet. Others, however, have recommended megadoses of up to 1,000 milligrams per day, or even more, on the principle that "if a little is good, more must be better," especially in resisting disease. In practice, such quantities can be obtained only by consuming the synthetic chemical.

A continuing role of nutritional chemistry is that of determining whether new kinds of food processing result in the destruction of vitamin C. For example, potatoes have been important in protecting northern Europeans from scurvy since their adoption as a major food staple in the eighteenth century. However, the process whereby they are converted to "instant" mashed potato powder destroys most of their vitamin C. Manufacturers therefore add synthetic ascorbic acid, so that the consumer receives the same benefit as that obtained from traditionally cooked potatoes.

Another disease that was associated with faulty diet by the end of the nineteenth century was beriberi, a potentially fatal condition first encountered by Europeans in the Dutch East Indies and Malaysia. Statistics from prisons and elsewhere indicated that it was associated with the use of white (i.e., highly milled) rice, rather than the cruder brown rice. The initial explanation was that, with the outer protective layers removed, white rice grains became contaminated by the penetration of toxic microorganisms through their porous surface. In a period when microorganisms were found to be responsible for so many diseases, the explanation seemed plausible. However, when it was discovered that chickens that had developed the same disease when fed white rice could be cured by the addition of the "branny layer" or "rice millings" to the white rice diet, the explanation seemed less satisfactory. Next it was realized that, if other starchy foods were substituted for white rice, the disease could still occur. Finally, it was accepted that this disease, and presumably others, could be explained by a lack of something, rather by positive toxicity. This became a central concept in the development of nutritional views.

The first attempts to isolate and identify the antiberiberi factor, using animals to test the activity of different materials, actually came before the corresponding work on the antiscorbutic factor. In 1912 Casimir Funk suggested that the factor in rice bran was a "vital amine," or "vitamine," and that a number of diseases were caused by a dietary lack of minute amounts of this or similar organic compounds. This proved to be true except that the compounds were not all of the chemical group called amines, and the term was reduced to vitamin. At least until the chemical structures of the factors became known, they were listed as vitamins A, B, C, and so forth. And when vitamin B, the water-soluble factor in yeast, was realized to be itself a complex of factors, these factors were called Bx, B2, B6, and so on. These code names have now been largely replaced by the corresponding chemical names, which in this case are thiamine, riboflavin, and pyridoxine for Bj, B2, and B6. Altogether 13 vitamins have been discovered.

Some species need other organic compounds in addition to the vitamins required by humans; others can synthesize vitamins. Dogs, pigs, and many other animals, for example, make their own vitamin C and thus thrive on a diet that would be scorbutic for human beings.

Because the animal kingdom, as a whole, lives on the vegetable kingdom, one would expect that all of the vitamins we in the animal kingdom require would be synthesized by plants. However, there were some puzzling exceptions for investigators to unravel. The first was vitamin A (or retinol), the fat-soluble factor, the lack of which resulted first in an inability to see in dim light and then in ulceration of the cornea of the eye and permanent blindness. The richest sources of the factor were fish liver oils; it was colorless and had characteristic chemical properties. Yet green leafy foods also prevented the deficiency, but apparently did not contain the same chemical. Finally it was discovered that green leafy foods contained a group of chemicals, the carote-noids, yellow, orange or red in color, which acted as provitamins - and were converted to the actual vitamin in the body.

Another disease to be associated with the lack of a fat-soluble vitamin was rickets, and again workers engaged in studying the cause of the disease obtained apparently contradictory results. Some reported that they could cure rachitic puppies by giving them exercise, that is, taking them for walks, without changing their diet. Others reported that they could cure the condition not by giving the puppies exercise but by supplementing their diet with fish liver oil - even if the oil had been oxidized so that it had lost its vitamin A activity. This paradox was resolved by a long series of studies showing that an active factor (to be named vitamin D) was produced by the action of the sun's ultraviolet rays on sterols, such as cholesterol, which animals synthesized for themselves. Vitamin D is synthesized in animal or human skin exposed to sunlight, after which it is stored in the liver.

The function of vitamin D was next related to the absorption of calcium and its deposition in bones. Rickets, which characteristically results in bent legs, occurs when bones are soft and undermineralized. The condition so prevalent in young children in Victorian cities was caused by inadequate irradiation of the skin, because of the pall of smoke from coal-burning homes and industries and the use of starch-based weaning formulas that lacked the vitamin. For a given amount of irradiation, less vitamin D is synthesized in people with pigmented skins than in people with less pigmentation. At the beginning of the twentieth century, a mild case of rickets was considered almost normal in the young children of black families who had migrated to northern industrial cities in the United States. It is still a problem among children of Asian immigrants in the United Kingdom.

Cobalamin (or vitamin B12), the last vitamin to date to be discovered (in 1948), is synthesized only by microorganisms. Ruminant animals obtain it from the bacteria living in their rumen (i.e., fore-stomach), and others from food with adhering soil bacteria. Omnivores, humans among them, obtain the vitamin from meat, fish, eggs, and milk.

As with ascorbic acid, the development of chemical analytic methods for determining the levels of each vitamin in foods and the inexpensive production of vitamins have enabled food manufacturers to fortify processed foods with them - without unduly raising their prices. Thus, margarine has vitamins A and D added at levels at least as high as those in butter, for which it is a substitute. White rice is fortified with thiamine, milk with vitamin D, and so on. In addition, many people in the more affluent countries take vitamin pills, or capsules, to ensure that they are receiving a sufficient dosage or in the hope of "superhealth," although there is no conclusive evidence that there is such a thing.

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Dieting Dilemma and Skinny Solutions

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