Ascorbic acid (vitamin C)

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Ascorbic acid (vitamin C)

Vitamin C, or ascorbic acid, is an essential dietary nutrient for a variety of biological functions. Under physiological conditions, it is fundamental in the biosynthesis of collagen through facilitating the hydroxylation of proline and lysine residues, thus allowing proper intracellular folding of pro-collagen for export and deposition as mature collagen. Vitamin C serves in humans also as a co-factor in several important hydroxylation reactions, such as the biosynthesis of catecholamines (through the conversion of dopamine to norepinephrine), L-carnitine, cholesterol, amino acids, and some peptide hormones.

Vitamin C is required for collagen synthesis by acting as a cofactor for non-heme iron α-ketoglutarate-dependent dioxygenases such as prolyl 4-hydroxylase. Vitamin C stimulates all types of collagen synthesis by donating electrons required for hydroxylation of proline and lysine in procollagen by specific hydroxylase enzymes. Collagen synthesis is required for maintaining normal vascular function but also for tumor angiogenesis. Vitamin C functions as a potent reducing agent that efficiently quenches potentially damaging free radicals produced by normal metabolic respiration of the body. At physiological concentrations, vitamin C is a potent free radical scavenger in the plasma, protecting cells against oxidative damage caused by ROS.

Ascorbic acid acts as co-factorfor the enzyme dopamine-β-hydroxylase, which catalyzes the conversion of neurotransmitter dopamine to norepinephrine. Thus ascorbic acid is essential for synthesis of catecholamines. In addition, ascorbic acid catalyzes other enzymatic reactions involving amidation necessary for maximal activity of hormones oxytocin, vasopressin, cholecystokinin and alpha-melanotripin. Ascorbic acid is also necessary for the transformation of cholesterol to bile acids as it modulates the microsomal 7 α-hydroxylation, the rate limiting reaction of cholesterol catabolism in liver.

All functions and activities of vitamin C in the organism provide antiaging effect by different mechanism.