Vitamin C, also called ascorbic acid, is powerful water-soluble antioxidant that is vital for the growth and maintenance of all body tissues. Though easily absorbed by the intestines, vitamin C cannot be stored in the body, and is excreted in the urine within two to four hours of ingestion. Humans, along with apes and guinea pigs, are the only species on the planet incapable of synthesizing vitamin C, and must therefore have access to sufficient amounts from adequate dietary sources or supplements in order to maintain optimal health.

One of vitamin C's most vital roles is in the production of collagen, an important cellular component of connective tissues, muscles, tendons, bones, teeth and skin. Collagen is also required for the repair of blood vessels, bruises, and broken bones.

Vitamin C helps regulate blood pressure, contributes to reduced cholesterol levels, and aids in the removal of cholesterol deposits from arterial walls, thus preventing atherosclerosis. Vitamin C also aids in the metabolization of folic acid, regulates the uptake of iron, and is required for the conversion of the amino acids L-tyrosine and L-phenylalanine into noradrenaline. The conversion of tryptophan into serotonin, the neurohormone responsible for sleep, pain control and well being, also requires adequate supplies of vitamin C.

A deficiency of ascorbic acid can impair the production of collagen and lead to joint pain, anemia, nervousness, retarded growth, reduced immune response, and increased susceptibility to infections. The most extreme form of vitamin C deficiency is called scurvy, a condition evidenced by swelling of the joints, bleeding gums, and the bursting, or hemorrhaging, of tiny blood vessels just below the surface of skin. If left untreated, scurvy is fatal. Before the discovery of lemons and limes as convenient sources of ascorbic acid, seafarers setting out on long ocean voyages could expect to lose up to two-thirds of a ships crew to scurvy. In acknowledgement of the the historical import of this well known and dreaded deficiency disease, in Latin, the word ascorbic means "without scurvy".

The recommended daily intake for vitamin c is 60 milligrams, but most health care professionals recognize that this tiny amount is barely enough to prevent the onset of scurvy, let alone confer any of the many well documented benefits of this amazing nutrient. Based on countless medical studies the therapeutic intake of ascorbic acid can be said to safely range from 500 to 4000 milligrams per day. Since this water-soluble vitamin is completely excreted from the body within 2 to 4 hours, and since the idea is to maintain stable serum levels for best results, the desired total daily dose should be divided into three separate doses and be taken throughout the day.

Foods highest in vitamin C include citrus fruits, potatoes, peppers, green leafy vegetables, tomatoes, and berries. Vitamin C is also available as a supplement in a wide range of forms such as pills, tablets, powders, wafers, and syrups. Generally doses range from 500 milligrams to 5000 milligrams depending upon the delivery system. Vitamin C activity is enhanced when taken with natural bioflavanoids such as hesperidn and rutin. Ascorbic acid works synergistically with vitamin E, meaning that both nutrients work more effectively together to extend their antioxidant effects.

While generally nontoxic, even in very large amounts, consuming vitamin C in large doses can lead to oxalic acid and uric acid stone formation unless consumed with plenty of water and supplemented with extra magnesium and vitamin B6. Taking large doses without slowly working up to the desired level can also cause temporary side effects such as diarrhea and skin rashes.