Ascorbic acid (as-KOR-bik AS-id), or vitamin C, is one of the most important dietary vitamins for humans because it plays a crucial role in building collagen, the protein that serves as a support structure for the body. It is a water-soluble vitamin, which means that the body excretes any excess vitamin C in the urine and cannot store a surplus. For that reason, humans must consume vitamin C in their daily diets. Vitamin C is found in many fruits and vegetables and most kinds of fresh meat. Citrus fruits, such as oranges and lemons, are especially rich in the compound.
L-ascorbic acid; vitamin C
Carbon, hydrogen, oxygen
191°C (376°F); decomposes
Soluble in water and alcohol; insoluble in ether, benzene, and chloroform
Humans have known about the consequences of vitamin C deficiency for centuries. People traveling long distances on land or by sea often came down with an illness called scurvy. The same illness struck people living in their own homes during long winters. The disease was characterized by pain and weakness in the joints, fatigue, bleeding gums, tooth loss, slow healing of wounds, and bruising. These symptoms were caused as the body's connective tissue broke down and small blood vessels ruptured. These symptoms began to disappear as fresh foods became more available. If they did not get enough fresh food in their diets, people could die of scurvy.
Scurvy was common enough that many people searched for its cause and cure. Sailors were especially vulnerable to the disease, and the first recorded investigations involving vitamin C were done by seafaring men. In 1536, French explorer Jacques Cartier (1491–1557) cured his sailors of scurvy by following the advice of Indians in Newfoundland, feeding them extract of pine needles. Scottish physician James Lind (1716–1794) began investigating the disease in 1747. He read many historical accounts of the diseases and combined that information with his own observations to deduce that scurvy occurred only among people with very limited diets. He went on a ten-week sea voyage and fed the solders various foods to see which ones were best at curing scurvy. Citrus fruits proved to be most effective in preventing the disease, a result that Lind reported in 1753. Captain James Cook (1728–1779) led expeditions to the South Seas in the late 1700s and kept his crew healthy by feeding them sauerkraut. In 1795 the British navy began serving its sailors a daily portion of lime juice, and two things happened: British sailors stopped getting scurvy, and people began calling sailors "limeys."
Many people refused to believe that scurvy was caused by a dietary deficiency, suggesting that it was instead the result of eating bad food or lack of exercise. In 1907, Norwegian biochemists Alex Holst (1861–1931) and Theodore Frohlich conducted a study in which guinea pigs were fed an experimental diet that caused them to develop scurvy. The link between the vitamin and the disease was firmly established by this research. Ascorbic acid was first isolated independently by the Hungarian-American biochemist Albert Szent-Györgi (1893–1986) and the American biochemist Charles Glen King (1896–1988) in 1932. It was synthesized a year later by the English chemist Sir Walter Norman Haworth (1883–1950) and the Polish-Swiss chemist Tadeusz Reichstein (1897–1996), again working independently of each other.
HOW IT IS MADE
Plants and most animals (humans and guinea pigs being two exceptions) synthesize vitamin C in their cells through a series of reactions in which the sugar galactose is eventually converted to ascorbic acid. For many years, the compound has been made commercially by a process known as the Reichstein process, named after its inventor Tadeusz Reichstein. This process begins with ordinary glucose, which is converted to another sugar, sorbitol, which is then fermented to obtain yet another sugar, sorbose. The sorbose is then converted step-by-step into a series of other products, the last of which is ascorbic acid.
Chemists have long been searching for an alternative to the Reichstein process because it uses so much energy and produces by-products that are hazardous to the environment. In the 1960s, Chinese scientists developed a method that involves only two steps in the synthesis of ascorbic acid, and in the early 2000s, Scottish scientists were attempting to develop a method that involved only a single step using fermentation. Currently, however, the Reichstein process remains the most popular method for making the compound.
- The vitamin C produced by plants and by synthetic methods are chemically identical and have identical effects in the human body.
- American chemist Linus Pauling (1901–1994) believed that very large doses of vitamin C could prevent and cure the common cold and other flu-like diseases. Because of his reputation (he won two Nobel Prizes, one in chemistry, as well as the Peace Prize), his viewpoint was highly respected. He was not, however, able to prove his theory to the satisfaction of his scientific colleagues.
COMMON USES AND POTENTIAL HAZARDS
The best known use of vitamin C is as a nutritional supplement, taken to ensure that one receives his or her daily minimum requirement of the vitamin. The recommended daily allowance (RDA) of vitamin C for adults is 60 milligrams per day. Anyone who eats a well-balanced diet that includes citrus fruits, tomatoes, and green leafy vegetables probably does not need to take a vitamin supplement. However, the amount of vitamin C one normally receives from a supplement is unlikely to cause any harm.
In addition to its nutritional uses, ascorbic acid has a number of other industrial applications, including:
- As a food preservative;
- As a reducing agent in chemical processes;
- As a preservative in foods;
- As a color fixing agent in meats, helping meats keep their bright red appearance;
- As an additive to bread dough, where it helps increase the activity of yeast used in the dough; and
- As a treatment for abscission in citrus plants, the tendency for a plant to lose its leaves, flowers, and fruits.
Words to Know
- Chemical reaction in which oxygen is removed from a substance or electrons are added to a substance.
- Chemical reaction in which some desired chemical product is made from simple beginning chemicals, or reactants.
FOR FURTHER INFORMATION
"Ascorbic Acid." International Programme on Chemical Safety. http://www.inchem.org/documents/icsc/icsc/eics0379.htm (accessed on September 21, 2005).
"L-Ascorbic Acid." University of Texas at Austin College of Engineering Department of Biomedical Engineering. http://www.engr.utexas.edu/bme/ugrad/UGLab/resources/MSDS/ascorbic%20acid.pdf (accessed on September 21, 2005).
Mead, Clifford, and Thomas Hager, eds. Linus Pauling: Scientist and Peacemaker. Portland, OR: Oregon State University Press, 2001.
Ascorbic acid or vitamin C is an antiscorbutic agent. Scurvy is a disease that potentially ranks as the second most important nutritional deficiency, after protein-calorie malnutrition. Scurvy, once common in among sailors, causes bleeding and inflamed gums, loose teeth, poor wound healing, pain in the joints, muscle wasting, etc. The structure of vitamin C is simple (see Figure 1), resembling a monosaccharide, and most animals are able to synthesize ascorbic acid. Only primates, guinea pigs, and some fruit bats have lost the ability to synthesize it.
Vitamins are organic molecules that mainly function as catalysts for reactions in the body. A catalyst is a substance that allows a chemical reaction to occur using less energy and less time than it would take under normal conditions.
Vitamin C is water-soluble and very important to all humans because it is vital to the production of collagen. Inside the cell, it helps form a precursor molecule called "procollagen" that is later packaged and modified into collagen outside the cell. Collagen is a gluelike substance that binds cells together to form tissues. It is the most abundant of the fibers contained in connective tissues. Connective tissue gives the human body form and supports its organs.
Vitamin C is also important as it helps protect the fat-soluble vitamins A and E, as well as fatty acids from oxidation . It is therefore a reducing agent and scavenger of radicals (sink of radicals). Radicals, molecules with unpaired electrons, are very harmful to the body as a result of their high reactivity, which may induce mutations and possibly cancer. Vitamin C, being an excellent source of electrons, can therefore donate electrons to free radicals such as hydroxyl and superoxide and quench their reactivity.
A debate exists over the anticancer properties of vitamin C. However, current evidence suggests that the major benefit of ascorbic acid with regard to cancer may be in reducing the risk of developing cancer, rather than in therapy. Vitamin C can work inside the cells to protect DNA (deoxyribonucleic acid), the hereditary material in cells, from the damage caused by free radicals. Also, it can reduce the development of nitrosamines (amines linked to the NO group) from nitrates, chemicals that are commonly used in processed foods. Once formed, nitrosamine can become carcinogenic (cancer-causing).
Sources of vitamin C are numerous: citrus fruits such as oranges, limes, and grapefruits and vegetables including tomatoes, green peppers, potatoes, and many others. The recommended dietary allowance (RDA) of vitamin C is 60 milligrams (0.0021 ounces) per day. An average American ingests about 72 milligrams (0.0025 ounces) a day. Some studies suggest higher daily doses especially for the elderly, women, and the infirm. For example, the late Linus Pauling, best known for his theory on chemical bonding and a two-time Nobel Prize winner, consumed several grams of vitamin C per day for the last forty years of his life and lived to age ninety-three.
see also Catalysis and Catalysts; Pauling, Linus.
Meisenberg, Gerhard, and Simmons, William H. (1998). Principles of Medical Biochemistry. St Louis, MO: Mosby.