Ascorbic acid--important for iron metabolism

Ascorbic acid is actively involved in the control of iron metabolism. It has long been known to enhance absorption of iron from test meals. At first this effect was ascribed to luminal reduction and solubilsation of iron. Later, molecular cloning of mammalian duodenal brush-border reductase activity and studies in animals and man strongly supported ascorbate as the intracellular electron donor for duodenal ferri-reductase activity and provided molecular mechanism for an intracellular role of ascorbate in intestinal iron absorption. Factors that alter duodenal ascorbate levels (dietary intake of ascorbate, dehydroascorbate, or oxidants) may therefore alter the rate of absorption. Ascorbate could play dual role in human cells; it could react as pro-oxidant and as antioxidant. The balance of these contradictory effects depends on ascorbate concentration. Pro-oxidant reactions predominate at low concentrations; at higher concentrations vitamin C reacts as antioxidant. The increase of plasma ascorbate in human iron deficiency, especially in females in active age, could explain gender-related biological variation of plasma levels of vitamin C. The possible participation of ferric reductase activity Dcytb in transferrin cycle in liver and in neutrophil host defense implies new aspects of the role of vitamin C in the regulation of iron homeostasis.