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Vitamin C Physiological Function

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In humans, vitamin C is essential to a healthy diet as well as being a highly effective antioxidant, acting to lessen oxidative stress; a substrate for ascorbate peroxidase;

Collagen, carnitine, and tyrosine synthesis, and microsomal metabolism
Ascorbic acid performs numerous physiological functions in human body. These functions include the synthesis of collagen, carnitine and neurotransmitters, the synthesis and catabolism of tyrosine and the metabolism of microsome. Ascorbate acts as a reducing agent (i.e. electron donor, anti-oxidant) in the above-described syntheses, maintaining iron and copper atoms in their reduced states.

Vitamin C acts as an electron donor for eight different enzymes: These reactions add hydroxyl groups to the amino acids proline or lysine in the collagen molecule via prolyl hydroxylase and lysyl hydroxylase, both requiring vitamin C as a cofactor. Hydroxylation allows the collagen molecule to assume its triple helix structure and making vitamin C essential to the development and maintenance of scar tissue, blood vessels, and cartilage.


2 are necessary for synthesis of carnitine. Carnitine is essential for the transport of fatty acids into mitochondria for ATP generation.
The remaining three have the following functions in common but do not always do this:
dopamine beta hydroxylase participates in the biosynthesis of norepinephrine from dopamine.
another enzyme adds amide groups to peptide hormones, greatly increasing their stability.
one modulates tyrosine metabolism.
Antioxidant
Ascorbic acid is well known for its antioxidant activity. Ascorbate acts as a reducing agent to reverse oxidation in aqueous solution. When there are more free radicals (Reactive oxygen species) in the body versus antioxidant, a human is under the condition called Oxidative stress. Oxidative stress induced diseases encompass cardiovascular diseases, hypertension, chronic inflammatory diseases and diabetes The plasma ascorbate concentration in oxidative stress patient (less than 45 µmol/L) measured is lower than healthy individual (61.4-80 µmol/L) According to McGregor and Biesalski (2006). This reaction can generate superoxide and other ROS. However, in the body, free transition elements are unlikely to be present while iron and copper is bound to diverse proteins. thus, ascorbate as a pro-oxidant is unlikely to convert metals to create ROS in vivo.

Immune system
Some advertisements claim that Vitamin C "supports" or is "important" for immune system function. These claims are partially supported by the scientific evidence (see Chandra RK, 1997, "Nutrition and the immune system: an introduction". The American Journal of Clinical Nutrition 66 (2): 460S–463S. PMID 9250133.)