follow-up. The relationship between smoking and depression has been extensively studied, but still remains equivocal (Glassman 1993; Covey et al. 1998). According to a twin study, the association between smoking and depression is not causal but arises largely from other factors that predispose to both smoking and depression (Kendler et al. 1993). The relationship between smoking and suicide is complicated by the fact that several suicide risk factors (e.g. depression, impulsivity-aggressiveness, alcohol consumption, poor physical health and disabilities, etc.) are more common among current smokers than among those who have never smoked (Degenhardt and Hall 2001; Ezzati and Lopez 2003; Munafo et al. 2007; Kahler et al. 2009). In the current study, information on smoking behavior was updated every two years, so that it could estimate more accurately the pack-years of smoking and time since quitting. Further, this study allowed to adjust for several potential confounders, including alcohol consumption, caffeine intake, and medical history, using updated and validated information.
