Cigarette smoking and risk of completed suicide: A meta-analysis of prospective cohort studies

Epidemiologic studies have reported conflicting results relating smoking to suicide risk. We conducted a meta-analysis of prospective cohort studies to evaluate the association of cigarette smoking with completed suicide. Eligible prospective cohort studies were identified from PubMed and EMbase databases (from 1966 to May 2011) and the reference lists of retrieved articles. Two authors independently extracted data and assessed study quality using the Newcastle–Ottawa Scale. Study-specific risk estimates were pooled using random-effects model and generalized least squares trend estimation was used to assess dose–response relationship. Fifteen prospective cohort studies involving 2395 cases among 1,369,807 participants were included in the meta-analysis. Our data suggested that cigarette smoking significantly increased the risk of completed suicide. Compared with never smokers, the pooled RR was 1.28 (95% CI: 1.001–1.641) for former smokers, and 1.81 (95% CI: 1.50–2.19) for current smokers, respectively. Subgroup analyses showed that the increased suicide risk among current smokers appeared to be consistent, although there was heterogeneity among studies of current smoking (p < 0.001). Significant dose–response relationship was found between smoking and suicide, and the risk of suicide was increased by 24% for each increment of 10 cigarettes smoked per day (RR, 1.24; 95% CI: 1.20–1.28). Our meta-analysis robustly demonstrates that cigarette smoking is associated with an increased risk of completed suicide, consistent with a dose–response relationship. This conclusion has an important public health message for countries with high smoking prevalence and high suicide rate such as China.