GSTM1 and atrial fibrillation: Among subjects with normal Hb levels (13–15.9 g/dL in men and 12–14.9 g/dL in women) at the first health checkup, both decrease and increase in Hb levels at the second measurement outside the normal ranges elevated AF risk by 11% and 21% for men and 3% and 27% for women, respectively, compared with those who maintained normal Hb levels (reference groups).