GSTM1 and anemia (phenotype): Two other studies based only on Hb levels reported the prevalence of anemia among teenagers in Najran (the south-western region of Saudi Arabia) (22.5% with a mean Hb value of 94 g/L) [19] and in Medina university students (with an overall prevalence of mild anemia (<110/dL) of 45%) [20].