In this large, population-based sample, active tobacco smoking was dose-dependently associated with increased risk of suicide, while former smoking was not, in a temporal sequence consistent with a causal relationship. This association held for all age groups, except the oldest, which was underpowered. The association remained after excluding those with reliably assessed antipsychotic and antidepressant medication use, psychiatric disability and tobacco-related somatic illness, including cancer. It also remained after adjusting for pre-existing depressiveness as a proxy for depressive illness, sedative–hypnotic use and excess alcohol use. Finally, in the first, to our knowledge, analysis among twin pairs who were doubly discordant for smoking and suicide, as a control for unmeasured genetic and environmental confounding, smoking was also strongly associated with suicide. Thus, this report extends findings from prior reports conducted from cohorts with shorter follow-up periods and fewer sources from which to control for confounders (Tanskanen et al. 2000; Iwasaki et al. 2005; Li et al. 2012; Lucas et al. 2013; Schneider et al. 2014) and implicates tobacco smoking as an environmental risk factor for suicide, indicating added risk for suicide independent of prior psychiatric and medical diagnosis or treatment.
