Cigarette smoking and suicidal behaviour: results from a 25-year longitudinal study

Background. This study examined the associations between cigarette smoking and suicidal ideation and suicide attempts, both before and after control for potentially confounding using fixed effects regression models. Method. Data were gathered during the Christchurch Health and Development Study, a 25-year longitudinal study of a birth cohort of New Zealand children (635 males, 630 females). The analysis was based on a sample of 1041 participants with available data on cigarette smoking and suicidal behaviour from ages 16 to 25 years. The main outcome measures were suicidal ideation and suicide attempts, ages 16-18,18-21, and 21-25. Results. There were significant bivariate associations between the frequency of cigarette smoking and both suicidal ideation and suicide attempts. Cohort members who smoked 20 or more cigarettes per day had odds of suicidal ideation that were 3.39 times (95% CI 2.06-5.59) those of non-smokers, and odds of suicide attempt that were 4.39 (95% CI 2.18-8.85) times those of non-smokers. Control for non-observed fixed confounding factors reduced the association between cigarette smoking and suicidal ideation and suicide attempts to statistical non-significance. After adjustment, those smoking more than 20 cigarettes per day had odds of suicidal ideation that were 1.00 times (95% CI 0.46-2.18) those of non-smokers, and odds of suicide attempt that were 1.84 (95% CI 0.81-4.18) times those of nonsmokers. Conclusions. The findings suggest that the associations between frequency of cigarette smoking and suicidal behaviour may largely be explained by the non-observed background factors and life circumstances that are associated with both cigarette smoking and suicidal behaviour.