The World Health Organization defines anemia as a hemoglobin (Hb) concentration of <13.0 g/dL for adult men and <12.0 g/dL for non-pregnant adult women, although slightly lower values can be found in older adults.4 Anemia is classified into the three types of microcytic, normocytic, and macrocytic, according to the mean corpuscular volume (MCV), which is calculated from the red blood cell count and the hematocrit value.5 This evidence concerns the gene GSTM1 and anemia (phenotype).