iron

iron An essential mineral. The average adult contains 4–5 g of iron, of which 60–70% is present in the blood as haem in the circulating haemoglobin, and the remainder present in myoglobin in muscles, a variety of enzymes, and tissue stores. Iron is stored in the liver as ferritin, in other tissues as haemosiderin, and as the blood transport protein transferrin.

Iron balance: losses in faeces 0.3–0.5 mg per day, in sweat and skin cells 0.5 mg, traces in hair and urine, total loss 0.5–1.5 mg per day. Blood loss leads to a considerable loss of iron. The average diet contains 10–15 mg, of which 0.5–1.5 mg is absorbed. The haem iron of meat and fish is considerably better absorbed than the inorganic iron of vegetable foods. Reference intakes are 8.7 mg for adult men and 14.8 mg for women; women who have heavy menstrual blood losses may not be able to obtain enough from food, and supplements are necessary.

Absorption of iron is aided by vitamin C taken at the same time as iron‐containing foods, and reduced by calcium, phosphate and phytic acid. Iron content of foods per 100 g: liver 6–14 mg, cereals up to 9 mg, nuts 1–5 mg, eggs 2–3 mg, meat 2–4 mg. Iron is added to flour so that it contains not less than 1.65 mg per 100 g. Fortified cereals provide 35% of the iron of British diets. Prolonged deficiency gives rise to anaemia.