Collagen synthesis
Vitamin C is a required cofactor for prolyl and lysyl hydroxylase, the enzymes that stabilize the triple helix of collagen. Without it, collagen fibers cannot cross-link properly, which is why classical scurvy shows up as bleeding gums, loose teeth, and wounds that will not close. Skin, tendons, blood vessels, and bone all depend on this pathway.
Immune cell function
White blood cells concentrate Vitamin C at levels 50 to 100 times higher than plasma. Neutrophils use it during the oxidative burst that kills pathogens, then depend on it again to protect themselves from their own reactive species. Lymphocyte proliferation and natural killer cell activity also fall when Vitamin C is low.
Antioxidant defense
Vitamin C donates electrons to neutralize free radicals in the aqueous compartments of the body. It also regenerates oxidized Vitamin E in cell membranes, effectively recycling another major antioxidant. This is the mechanism behind its role in oxidative stress from infection, exercise, alcohol, and pollution.
Neurotransmitter synthesis
Dopamine beta-hydroxylase, the enzyme that converts dopamine to norepinephrine, requires Vitamin C. It is also involved in the synthesis of certain peptide hormones and in modulating catecholamine release under stress. Brain tissue holds some of the highest Vitamin C concentrations in the body.
Iron absorption and metabolism
Vitamin C reduces dietary iron from the ferric to the ferrous form, dramatically improving absorption from plant sources. It also participates in mobilizing stored iron. This is one reason low Vitamin C and low iron often show up together in the same patient.