In addition to the strong effect of CYP2A6 and other genetic influences, NMR is also influenced by various demographic and hormonal factors. According to a recent study [17], factors affecting NMR include ethnicity, likely due to the varying frequency of reduced activity CYP2A6 variants among different ethnicities [13]. Other affecting factors include sex, hormone replacement therapy, and use of estrogen containing contraceptive pills, all related to CYP2A6 being induced by estrogen [18], as well as body mass index (BMI), alcohol consumption, and cigarette consumption [17]. Altogether these above mentioned factors were estimated to account for approximately 8% of inter-individual variance in NMR [17].
