Vitamins are essential nutrients required in the diet of organisms because those organisms cannot synthesize the vitamins by themselves. Vitamin C, also known as ascorbic acid, is only required for a few vertebrates, including humans and other primates, guinea pigs, fruit-eating bats, some birds, and certain fish. These organisms cannot synthesize vitamin C because they lack a liver enzyme, L-glulono-g-lactone oxidase. Good dietary sources of vitamin C include broccoli, cabbage, tomatoes, berries, cantaloupe, mango, papaya, strawberries, and citrus fruits.
Ascorbic acid (vitamin C) serves its biochemical function as a reducing agent. It prevents the disease scurvy; plays important roles in the brain, nervous system, and immune system; mobilizes iron in the body; prevents anemia; and has many other recently discovered health benefits.
Vitamin C was first isolated in 1928 by Albert Szent-Györgyi, and its structure was determined by Hirst and Haworth in 1933. For this work, Szent-Györgyi and Haworth received the Nobel Prize in 1937.
Vitamin C and Collagen
Collagen is a rigid, fibrous protein that is the principal constituent of connective tissue in animals, including bones, teeth, cartilage, tendons, skin, and blood vessels. Collagen's high tensile strength is due to the unique structure of its basic structural unit, tropocollagen, which consists of three left-handed helical polypeptide chains intertwined around each other in a right-handed triple helix (right).
Collagen has a unique amino acid composition, with nearly one-third of the amino acid residues being glycine, and containing many unusual modified amino acids. Two of these modified amino acids crucial to the structural properties of collagen, 3-hydroxyproline and 4-hydroxyproline (shown below), are produced by post-translational modification of proline residues by the enzyme prolyl hydroxylase, which requires vitamin C. So you can see why a deficiency in vitamin C would result in a severe compromise in the integrity of connective tissue, resulting in scurvy.
Vitamin C and Scurvy
Vitamin C has a long history. Dietary deficiencies of this essential vitamin leads to the disease known as scurvy. As early as the 15th century, when the imperialistic countries of Europe sent explorers to stake new territories for their king and queen, navigators dreaded the onset of scurvy amongst the crew of their vessels during their long voyages at sea. This is best exemplified by Vasco da Gama's voyage around the Cape of Good Hope in 1498, where he lost 100 men out of 160 to the disease. It has even been noted that ghost ships rode the seas at times, for everyone aboard had perished from the disease. Scurvy was characterized by lesions in the skin and blood vessels, eventually leading to grotesque disfigurement and death unless treated.
It is therefore understandable that the causes of this disease and the treatment thereof were of great concern, but it wasn't until 1753 that the then effectual methods for treating the disease were debunked by James Lind, in his Treatise on Scurvy. His proper diagnosis for the cause of scurvy was "want of fresh vegetables and greens," and he recommended the extract of lemons for the prevention and cure.
Captain James Cook, an English navigator in the Royal Navy whose accomplishments include surveying the St. Lawrence Channel, and exploring the coasts of Labrador, Newfoundland, New Zealand, and Australia, was the first to employ the advice of James Lind on his voyage circumnavigating the globe. His report was awarded the Copley Medal of the Royal Society in 1776, and prompted the frequent diet of lemon and lime extract by soldiers in the British Navy, who would forever after be labeled "limeys." Later, Captain Cook discovered Hawaii while trying in vain to discover a northwest passage between the Atlantic and Pacific oceans from the west, and was killed in a skirmish with the natives there.
Reading Captain Cook's letter on "The Method Taken for preserving the Health of The Crew of His Majesty's Ship, the Resolution," one can see the rigorous promotion of fruits and vegetables in the diet of the crew by the navigator, as well as a great attention to other matters such as the ventilation and cleanliness of the ship.
Vitamin C and Health Benefits
The famed Dr. Linus Pauling was a great proponent of the nutritional sciences. His accomplishments include a Nobel Prize in 1954 for his work investigating the nature of the chemical bond and the elucidation of complex structures such as the a-helix, as well as a Nobel Peace Prize in 1962 for his efforts to ban nuclear testing. He believed that vitamins, in particular vitamin C, were crucial to health, and his book, How to Live Longer and Feel Better, advocated taking megadose amounts to fight cancer, the common cold, heart disease, and possibly AIDS.
Recall that ascorbic acid is a reducing agent. Because of this biochemical trait, it serves as an antioxidant in the body. Cancer can be caused by oxidation of DNA, causing mutations in genes that are important for proper regulation of the cell cycle, and resulting in uncontrolled proliferation of the affected cell, culminating in tumor formation. Antioxidants such as vitamin C mop up stray oxidizing agents in the cell, limiting their ability to damage DNA, thereby greatly slowing down rates of cancer in the body.
Because of these health benefits associated with vitamin C, in April 1999, the NIH recommended tripling the FDA-recommended daily intake to 200 mg.
Vitamin C Web Site Links
Linus Pauling's Last Interview - He illustrates his controversial views on vitamins, cancer, and the medical profession. Very convincing!
C for Yourself - Great general site on vitamin C and health.
The NIH Office of Dietary Supplements - Find out what's proven and what's bunk regarding dietary supplements (including vitamin C)...backed by actual research. Pay special attention to the IBDS Database of relevant scientific literature.
Vitamin C: Immune Cell Antidote? - Describes one benefit of vitamin C in immune system. function.
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