The World Health Organization (WHO), the American Gastroenterological Association (AGA) and the Russian National Hematology Society (RNHS) define iron deficiency anemia as blood Hb levels below 130 g/L in men and below 120 g/L in nonpregnant women, and ferritin levels < 15 μg/L (WHO guidelines) or < 11.0 μg/L in addition to the related clinical symptoms (RNHS guidelines). Here, GSTM1 is linked to anemia.