Iron and vitamin C

Hallberg and colleagues measured iron absorption from bread rolls enriched with phytates, compounds in whole grains and legumes that bind iron. The effect depended on the dose: 2 mg of phytates reduced absorption by 18%, 25 mg by 64% and 250 mg by 82%. Adding vitamin C clearly counteracted this inhibition, whereas the effect of meat was less clear.

Cook and Reddy measured iron absorption in 12 people over three 5-day periods, with vitamin C intakes ranging from 51 to 247 mg per day. Average absorption did not differ between the periods. The statistical analysis did find a positive association with vitamin C, but it was much weaker than for a single meal. According to the authors, this explains why several studies found no effect of prolonged vitamin C supplementation on iron stores.

Li and colleagues divided 440 adults with iron-deficiency anemia, 97% of whom were women, into two groups: 100 mg of iron every 8 hours, with or without 200 mg of vitamin C, for 3 months. After 2 weeks, hemoglobin had increased by 2.00 g/dL with vitamin C and by 1.84 g/dL without it, a difference considered equivalent. After 8 weeks, ferritin had increased by about 35 ng/mL in both groups. Adverse effects were the same, at around 21%.

If your iron comes mainly from plants, having a vitamin C-rich food at the same meal is a reasonable way to help. For a prescribed iron supplement, vitamin C is not necessary according to the Li trial. Iron supplementation should be justified by blood test results, not taken by default. To learn more, see the table of iron-rich foods , our article on low ferritin and our comparison liposomal or standard vitamin C .

Hallberg's measurements concern single test meals. Cook's study included only 12 people. Li's trial was conducted in a single hospital, was open-label, and used a high iron dose (300 mg per day): its conclusions do not necessarily apply to low doses or alternate-day dosing. None of these studies measured digestive tolerability specific to the combination.