The species-specific loss in the ability to synthesize ascorbate strikingly parallels the evolutionary loss of the ability to break down uric acid. Uric acid and ascorbate are both strong reducing agents (electron-donors). This has led to the suggestion [4] that in higher primates, uric acid has taken over some of the functions of ascorbate.
Vitamin C was first isolated in 1928, and in 1932 it was proved to be the agent which prevents scurvy. Both Charles Glen King at the University of Pittsburgh and Albert Szent-Györgyi (working with ex-Pittsburgh researcher Joseph Svirbely) came to discover what is now known as Vitamin C around April of 1932. Although Szent-Gyorgyi was awarded the 1937 Nobel Prize in Medicine, many feel King is as responsible for its development if not more so. [5][6]

Vitamin C is a weak acid, called ascorbic acid or a salt ascorbate. It is the L-enantiomer of ascorbic acid. The D-enantiomer shows no biological activity. Both are mirror image forms of the same chemical molecular structure (see optical isomers).

The active part of the substance is the ascorbate ion, which can express itself as either an acid or a salt of ascorbate that is neutral or slightly basic. Commercial vitamin C is often a mix of ascorbic acid, sodium ascorbate and/or other ascorbates. Some supplements contain in part the D-enantiomer, which is useless and harmless. See the ascorbic acid article for a full description of the molecule's chemical properties.

Functions in the body
As a participant in hydroxylation, vitamin C is needed for the production of collagen in the connective tissue. These fibers are ubiquitous throughout the body, providing firm but flexible structure. Some tissues have a greater percentage of collagen, especially: skin, mucous membranes, teeth and bones. 
Vitamin C is required for synthesis of dopamine, noradrenaline and adrenaline in the nervous system or in the adrenal glands. 
Vitamin C is also needed to synthesize carnitine, important in the transfer of energy to the cell mitochondria. 
The tissues with greatest percentage of vitamin C — over 100 times the level in blood plasma — are the adrenal glands, pituitary, thymus, corpus luteum, and retina. 
The brain, spleen, lung, testicle, lymph nodes, liver, thyroid, small intestinal mucosa, leukocytes, pancreas, kidney and salivary glands usually have 10 to 50 times the concentration present in plasma. 
Vitamin C is an antioxidant and acts as a substrate for ascorbate peroxidase. 

Vitamin C deficiency
No bodily organ stores ascorbate as a primary function, and so the body soon depletes itself of ascorbate if fresh supplies are not consumed through the digestive system, eventually leading to the deficiency disease known as scurvy (a form of avitaminosis), which results in illness and death if consumption of vitamin C is not resumed in time.

Therapeutic applications and doses
Vitamin C is needed in the diet to prevent scurvy, however, from the time it became available in pure form in the 1930s, some practitioners experimented with vitamin C as a treatment for diseases other than scurvy.
 

Colds
At least 29 controlled clinical trials (many double-blind and placebo-controlled) involving a total of over 11,000 participants have been conducted. These trials were reviewed in the 1990s [5][6] and again recently.[16] The trials show that vitamin C reduces the duration and severity of colds but not the frequency. The data indicate that there is a normal dose-response relationship. Vitamin C is more effective the higher the dose. 

Heart disease
Vitamin C is the main of the three ingredients in Linus Pauling's patented preventive cure for heart disease, the other two being the amino acid lysine and nicotinic acid (a form of Vitamin B3). This treatment is not supported by mainstream medical science.[citation needed]

Viral diseases, and poisons
Orthomolecular medicine and a minority of scientific opinion sees vitamin C as being a low cost and safe way to treat viral disease and to deal with a wide range of poisons.

Vitamin C has a growing reputation for being useful in the treatment of colds and flu, owing to its recommendation by prominent biochemist Linus Pauling. In the years since Pauling's popular books about vitamin C, general agreement by medical authorities about larger than RDA amounts of vitamin C in health and medicine has remained elusive. Ascorbate usage in studies of up to several grams per day, however, have been associated with decreased cold duration and severity of symptoms, possibly as a result of an antihistamine effect [23]. The highest dose treatments, published clinical results of specific orthomolecular therapy regimes pioneered by Drs. Klenner (repeated IV treatments, 400-700+ mg/kg/day [24][25]) and Cathcart (oral use to bowel tolerance[4], up to ~150 grams ascorbate per day for flu), have remained experimentally unaddressed by conventional medical authorities for decades.

Lead poisoning
There is also evidence that Vitamin C is useful in preventing lead poisoning, possibly helping to chelate the toxic heavy metal from the body. [27]
 

Cancer
In 2005 in vitro research by the National Institutes of Health indicated that Vitamin C administered in pharmacological concentrations (i.e. intravenous) was preferentially toxic to several strains of cancer cells. The authors noted: "These findings give plausibility to intravenous ascorbic acid in cancer treatment, and have unexpected implications for treatment of infections where H2O2 may be beneficial." This research appeared to support Linus Pauling's claims that Vitamin C can be used to fight cancer.
 

Cataracts
It has been also suggested that Vitamin C might prevent the formation of cataracts. [8]