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Vitamin C is an essential cofactor for mixed-oxidase enzymes which catalyze the production of many proteins such as those involved in building supporting tissue in the body.
It is almost completely absorbed at doses of 200-400 mg/day, and plasma concentrations plateau at 60-80 μmol/L. Excess vitamin C in the gut is largely excreted. This absorption barrier may be overcome by administration of a direct intravenous infusion of vitamin C, which leads to high plasma levels.
These will slowly return to normal via urinary excretion. At doses lower than 200 mg/day, absorption is directly proportional to the dosage. Plasma levels of vitamin C are thus controlled largely by intestinal absorption, renal reabsorption and tissue transport mechanisms.
Dietary reference intakes may be classified as:
The following table shows the recommended daily allowance of vitamin C in various groups:
Table 1. RDA of vitamin C