Prolonged absolute iron deficiency leads to the emergence of iron deficiency anaemia (IDA), defined according to World Health Organization (WHO) criteria as Hb <120 g/L in women (<110 g/L in pregnant women) and <130 g/L in men (although these levels represent lower limits of normal Hb – levels are typically much higher in healthy individuals). Here, GSTM1 is linked to Iron deficiency anemia.