GSTM1 and anemia (phenotype): Among them are one research from the Central Vietnam region,16 nine studies from the Northern Vietnam region,14,15,17-19,21,23-25 one national study,20 and one study on a large-scale.22 Additionally, there were six studies from plain areas,14,15,17,21,23,25 four studies from mountain areas,16,18,19,24 and one study from both plain and mountain areas.22 Haemoglobin (Hb) values below 12.0 g/dL or 120 g/L were utilized for all included studies as the diagnostic threshold for anaemia among non-pregnant women of reproductive-aged 15–49 years old.