Last revised by Daniel J Bell on 10 Jul 2021

Iron (chemical symbol Fe) is one of the trace elements that is essential for normal human health due to its central importance in the structure and function of hemoglobin and the cytochromes.

Iron is a transition metal with atomic number 26 and an atomic weight of 55.847 g/mol. It exists in two main oxidation states: ferric (Fe (III) or Fe3+) and ferrous (Fe (II) or Fe2+) forms. 

There are four stable isotopes of iron, of which iron-56, the commonest on earth accounts for 91.7%, whilst iron-54, the second commonest isotope comprises a further 5.8%. Iron-57 comprises most of the rest of global iron (2.1 %) and iron-58 only a tiny percentage (0.2%) 4. A further 27 unstable isotopes are known, with the one showing most promise in nuclear medicine being iron-52 (half-life 8.3 hours), which is a positron emitter and is used for PET 4,5.

In the normal diet iron may be found in meat, eggs, cereals, and some fruits and vegetables. 

Generally iron in food is in the ferric (Fe3+) form but the body absorbs elemental iron in the ferrous (Fe2+) form. Reduction from ferric to ferrous forms is assisted to a great extent by gastric juice, which puts the iron into solution and allows it to complex with ascorbic acid (vitamin C) and other substances that reduce the iron. This is reflected in the iron deficient state that results following a removal of part or all of the stomach, without adequate iron replacement therapy.

Iron is of central importance as a key constituent of:

  • hemoglobin (therefore iron is also a hematinic)
  • myoglobin 
  • cytochromes in the electron transport chain 

Primarily results in iron-deficiency anemia.

Iron-containing fumes have been implicated as a precipitant in metal fume fever, although this is contentious 3.

  • iron-52 in PET 4,5
  • iron-59, used for many years for ferrokinetic research and clinical use 4,5

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