Vitamin C in Human Health: Biochemistry, Physiology, and Pathophysiology

Abstract

Ascorbic acid (vitamin C) is a water-soluble micronutrient essential for various physiological processes in humans, who must obtain it through diet due to an inability to synthesize it endogenously. Functioning as a potent antioxidant and a cofactor for numerous enzymes, vitamin C plays critical roles in collagen biosynthesis, immune support, wound healing, and the maintenance of skin health. It is actively accumulated in body tissues, especially the skin, where it protects against oxidative stress and promotes dermal integrity. In collagen formation, vitamin C acts as a cofactor for prolyl and lysyl hydroxylases within the endoplasmic reticulum, enabling hydroxylation of proline and lysine residues—key modifications for the structural integrity, folding, and extracellular secretion of collagen fibrils. As an antioxidant, it neutralizes reactive oxygen species and works synergistically with other antioxidants, while at high concentrations, it may exhibit pro-oxidant behavior in the presence of transition metals. In the immune system, vitamin C enhances cellular functions and reduces susceptibility to infections. Deficiency leads to scurvy, marked by impaired collagen synthesis, hemorrhages, poor wound healing, and in severe cases, fatal complications. Ascorbic acid also contributes to neurotransmitter synthesis and cholesterol metabolism. Dietary sources rich in ascorbic acid include citrus fruits, berries, and cruciferous vegetables, with intestinal absorption mediated primarily by sodium-dependent vitamin C transporters (SVCT1 and SVCT2). Given its diverse biological roles, adequate intake of vitamin C is essential for maintaining homeostasis and mitigating oxidative and inflammatory pathologies.