Ascorbic Acid (Vitamin C)

The active form of vitamin C is ascorbic acid (Fig. 1). Its main function is as a reducing agent. Vitamin C is a coenzyme in hydroxylation reactions (for example, hydroxylation of prolyl and lysyl residues in collagen),where its role is to keep the iron (Fe) of hydroxylases in the reduced, ferrous (Fe⁺²) form. Thus, vitamin C is required for the maintenance of normal connective tissue as well as for wound healing. Vitamin C also facilitates the absorption of dietary nonheme iron from the intestine by reduction of the ferric form (Fe⁺³) to Fe⁺² .

Figure 1: Structure of ascorbic acid.
A. Deficiency
Ascorbic acid deficiency results in scurvy, a disease characterized by sore and spongy gums, loose teeth, fragile blood vessels, hemorrhage, swollen joints, bone changes, and fatigue (Fig. 2). Many of the deficiency symptoms can be explained by the decreased hydroxylation of collagen, resulting in defective connective tissue. A microcytic anemia caused by decreased absorption of iron may also be seen.

Figure 2: Oral manifestations in a patient with scurvy.
B. Chronic disease prevention
Vitamin C is one of a group of nutrients that includes vitamin E and β-carotene , which are known as antioxidants. [Note: Vitamin C regenerates the functional, reduced form of vitamin E.] Consumption of diets rich in these compounds is associated with a decreased incidence of some chronic diseases, such as cardiovascular disease (CVD) and certain cancers. However, clinical trials involving supplementation with the isolated antioxidants have failed to demonstrate any convincing preventive effects.