Out of all of the vitamins, vitamin C (or ascorbic acid or 2-oxo-L-threo-hexono-1,4- lactone-2,3-enediol or
(R)-3,4-dihydroxy-5-((S)- 1,2-dihydroxyethyl)furan-2(5H)-one!) is probably the most well known.
Image kindly reproduced according to the licence at: http://en.wikipedia.org/wiki/File:L-Ascorbic_acid.svg
Image kindly reproduced according to the licence at: http://en.wikipedia.org/wiki/File:Ascorbic-acid-from-xtal-1997-3D-balls.png
Vitamin C is an antioxidant. An antioxidant is capable of stopping the oxidation of other molecules. Humans have lost the gene (through mutations) that is responsible for making ascorbic acid and so it must be obtained through the diet. Other animals do not need it in their diet.
The reactions in cells can produce hydrogen peroxide (H2O2), hypochlorous acid (HOCl), and free radicals such as the hydroxyl radical (·OH) and superoxide (O2−). These oxidants can damage cells for example, by oxidising DNA, causing mutations and or cancer.
An understanding of the need for ‘something’ in the diet came to fruition in the 1750’s, often attributed to the Englishman James Lind. Lind was a ships surgeon for the British Royal Navy who realised that there was something in fruit that stopped sailors developing scurvy, a disease caused by the lack of vitamin C in the diet.
Scurvy manifests itself as lethargy but leads to spots on the skin, bleeding mucous membranes, open wounds that do not heal, loss of teeth, jaundice and eventually death. This was a huge problem on long sea journeys as fresh food could not be stored and sailors were issued with rations of dry food – which lacked vitamin C. Lind gave some men on the ship oranges and lemons, whilst others did not have this luxury. The men receiving the fruit were noticeably fitter than the men who doid not receive it and it is one of the first examples of a controlled medical trial.