Iron-deficiency anaemia and haemoglobin. Artwork of irregularly shaped red blood cells (red) in a patient suffering from iron-deficiency anaemia. At centre is a molecule of haemoglobin, the blood pigment that carries oxygen. Haemoglobin consists of chains of amino acids folded into four globin subunits (blue and pink). The haem groups (green) surround the iron atoms (blue) which can bind to oxygen atoms (red spheres). Iron-deficiency anaemia is caused by a deficiency of iron, an essential component of haemoglobin. Many of the cells are irregularly shaped and this reduces their oxygen-carrying capacity. Symptoms include tiredness, dizziness and a pale skin.