Vitamin C is the term covering several compounds that form an essential human nutrient, including ascorbic acid and ascorbate. It is a water-soluble vitamin which cannot be endogenously synthesised and must be supplied by the diet.
It contributes to the synthesis of collagen, producing symptoms of scurvy when the vitamin is lacking. It also helps to prevent bleeding from the capillaries and to heal wounds. Perhaps its most valuable function is that ascorbate is an antioxidant, protecting cells against oxidative stress and the damage caused by free radicals.
Vitamin C is traditionally believed to be effective in combating inflammatory infections such as colds and flu. It is certainly present in high concentrations in the immune cells, and gets used up very quickly during the course of an infection, suggesting that the tradition is valid, though so far research has not revealed exactly how it works.
The best dietary sources of vitamin C are vegetables and fruit, especially rosehips, chilli peppers, blackcurrants and parsley, and some meat, particularly liver. Vitamin C is the nutritional supplement most commonly purchased and comes in a variety of forms, including crystals, tablets, cold remedy powders and energy drink mixes.