Purpose: To clarify whether cigarette smoking was associated with completed suicide in a cohort of middle-aged Japanese men.
Methods: A total of 45,209 out of 57,714 men, aged 40 to 69 years, in nine public health centers across Japan responded to a self-administered questionnaire that included questions regarding their smoking history. The questionnaire was distributed in 1990 (Cohort I) and in 1993 and 1994 (Cohort II). By the end of 2000, 173 suicides were identified by death certificates.
Results: After adjusting for potential confounders, current smokers had a marginally higher risk of suicide than never smokers. Current smokers with more than 60 pack-years of cigarette smoking had a more than two-fold higher risk of suicide than never smokers (pooled multivariate relative risk=2.1; 95% confidence interval, 1.1, 4.0), but a significant dose-response relationship between pack-years of smoking and suicide was not found. The risk of suicide increased significantly with increasing numbers of cigarettes smoked per day (p for trend=0.036). Smoking status, duration of quitting, duration of smoking, and age at the start of smoking were not significantly associated with suicide risk.
Conclusion: Our results suggest that heavy smoking, particularly a large number of cigarettes per day at baseline was associated with an increased risk of suicide independent of several potential confounders.