Vitamin C belongs to a group of water-soluble vitamins, ubiquitously present in a variety of fruits and vegetables. In organisms, Vitamin C can exist in two forms: reduced—the exact ascorbic acid (AA) which in physiological pH occurs in its anion form of an ascorbate—and oxidized one—dehydroascorbic acid (DHA), which is a product of two-electron oxidation of AA. In the course of metabolic processes an ascorbate free radical can be produced as a result of one-electron oxidation. This variety may subsequently undergo dismutation forming ascorbate and DHA.
Most mammalian organisms are generally capable of synthesizing Vitamin C themselves. However, some species like fruit bats, guinea pigs, other primates and humans are deprived of this ability due to the lack of l-gulono-1,4-lactone oxidase enzyme which is an element of the metabolic pathway responsible for synthesis of ascorbic acid from glucose. Moreover, Vitamin C is not produced by intestinal microflora, therefore ascorbate levels in the human body are strictly dependent on dietary intake and therapeutic supplementation.
The recommended nutritional levels of Vitamin C suggest that intake should be 75 mg (women) and 90 mg(men) per day, whereas in smokers this value ought to be increased by 35 mg per day. There are other considerations and cofactors which may require much higher doses due to excessive oxidative stress levels, and more rapid rate of ascorbate depletion.
