Vitamin C and oral iron: why take iron tablets with orange juice
Vitamin C converts ferric iron (Fe3+) into ferrous iron (Fe2+), the form that the duodenum can absorb, so orange juice taken with oral iron tablets increases absorption.
Remember
Orange juice helps iron tablets because its vitamin C converts ferric iron into the ferrous form, whereas tannins in tea bind iron and reduce its absorption.
Iron in the diet comes in two forms. Haem iron comes from meat and enters by its own route. Non-haem iron, the type in plant foods, is a mixture of ferrous (Fe2+) and ferric (Fe3+) iron, and iron tablets are a source of non-haem iron.
Only the ferrous form can be taken up in the duodenum and upper jejunum (the first parts of the small intestine). Vitamin C is a reducing agent, which means it donates electrons, so it converts ferric iron into ferrous iron in the gut lumen. The ferrous iron is then carried into the enterocytes (the absorptive cells lining the gut) by a transporter protein called DMT1, and a larger share of the dose reaches the blood.
Some everyday items do the reverse. Tea and red wine contain tannins, while wholemeal products and chapattis contain phytates. Both bind non-haem iron in the intestine and reduce how much of it is absorbed. Antacids (medicines that reduce stomach acidity) also reduce absorption.
That is why a patient on iron tablets is told to take them with citrus juice rather than with meals or with tea. Vitamin C also keeps iron dissolved in the alkaline duodenum and can counter the effect of inhibitors such as tea. A useful rule is that citrus helps and tea hinders.
Key facts
- Absorbed form
- ferrous iron (Fe2+) is the form taken up in the duodenum and upper jejunum.
- Vitamin C
- it is a reducing agent that converts ferric (Fe3+) iron into ferrous (Fe2+) iron in the gut lumen.
- Uptake
- ferrous iron crosses into the enterocytes through the transporter DMT1.
- Inhibitors
- tea and red wine (tannins), chapattis and wholemeal products (phytates) and antacids lower absorption.
- Haem iron
- iron from meat uses its own route of uptake and does not need vitamin C.
- Practical advice
- take iron tablets with orange juice and not with tea.
Exam traps
- Vitamin C does not increase transferrin, which is made in the liver and carries iron through the blood once it has been absorbed, so transferrin does not control uptake in the gut.
- Tea does not help iron tablets: its tannins bind non-haem iron in the gut and reduce absorption.
- Ferroportin, the protein that exports iron from the enterocyte into the blood, works after iron has entered the cell, whereas vitamin C acts earlier, in the gut lumen.
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