A metal which is an essential constituent of the red blood corpuscles, where it is present in the form of HAEMOGLOBIN. It is also present in muscle as MYOGLOBIN, and in certain respiratory pigments which are essential to the life of many tissues in the body. Iron is absorbed principally in the upper part of the small intestine. It is then stored: mainly in the liver; to a lesser extent in the spleen and kidneys, where it is available, when required, for use in the bone marrow to form the haemoglobin in red blood corpuscles. The daily iron requirement of an adult is 15–20 milligrams. This requirement is increased during pregnancy.
The main use of iron is in the treatment of iron-deficiency anaemias. (See ANAEMIA.) Iron preparations sometimes cause irritation of the gastrointestinal tract, and should therefore always be taken after meals. They sometimes produce a tendency towards constipation.