The region on chromosome 19 encompassing CYP2A6 is genome-wide significantly associated with cigarettes per day in large meta-analyses of European ancestry adults (TAG, 2010; Thorgeirsson et al., 2010). Among nicotine dependent adults, several studies demonstrate that slower metabolizers smoke fewer cigarettes per day (Benowitz, 2008; Malaiyandi et al., 2005). This observation is thought to reflect that smokers naturally titrate cigarette consumption to maintain steady nicotine levels.
