Ascorbic acid is necessary for many physiologic functions, including the metabolism of iron. The absorption of nonheme iron (primarily from plant sources) from the intestinal tract depends on iron being in its reduced form. (Heme iron, found in meat, fish, and poultry, appears to be absorbed intact.) Ascorbic acid, by maintaining iron in the ferrous state, can enhance the absorption of oral iron, however, the magnitude of this increase is in the range of 10% and only occurs with doses of ascorbic acid, vitamin C of 500 mg or greater. Healthy individuals usually absorb iron supplements (e.g., iron salts or polysaccharide-iron complex) adequately from the GI tract, but some patients may benefit from receiving supplemental ascorbic acid with each oral iron dose.
Patients should be advised not to take ascorbic acid, vitamin C supplements along with deferoxamine chelation therapy unless such supplements are prescribed with the approval of their health care professional. Patients with iron overload usually become vitamin C deficient, probably because iron oxidizes the vitamin. Vitamin C can be a beneficial adjunct in iron chelation therapy because it facilitates iron chelation and iron complex excretion. As an adjuvant to iron chelation therapy (e.g., deferoxamine), vitamin C (in doses up to 200 mg/day for adults, 50 mg/day in children < 10 years of age or 100 mg/day in older children) may be given in divided doses, starting after an initial month of regular treatment with deferoxamine. However, higher doses of ascorbic acid, vitamin C can facilitate iron deposition, particularly in the heart tissue, causing cardiac decompensation. In patients with severe chronic iron overload, the concomitant use of deferoxamine with > 500 mg/day PO of vitamin C in adults has lead to impairment of cardiac function; the dysfunction was reversible when vitamin C was discontinued. The manufacturer of deferoxamine recommends certain precautions for the coadministration of vitamin C with deferoxamine. First, vitamin C supplements should not be given concurrently with deferoxamine in patients with heart failure. Secondly, in other patients, such supplementation should not be started until 1 month of regular treatment with deferoxamine, and should be given only to patients receiving regular deferoxamine treatments. Do not exceed vitamin C doses of 200 mg/day for adults, 50 mg/day in children < 10 years of age, or 100 mg/day in older children, given in divided doses. Clinically monitor all patients, especially the elderly, for signs or symptoms of decreased cardiac function.