Background: A link between cigarette smoking and suicidal behavior has been reported in clinical and epidemiological studies.
Objective: To examine the association between smoking and suicidal thoughts or attempt in a longitudinal study, in which proximate status of smoking and psychiatric disorders in relation to timing of suicidal behaviors is taken into account.
Design: A longitudinal study of young adults interviewed initially in 1989, with repeated assessments over a 10-year follow-up.
Setting and participants: The sample was selected from a large health maintenance organization representing the geographic area, except for the extremes of the socioeconomic range. The response rate at each follow-up (3, 5, and 10 years after baseline) exceeded 91%.
Main outcome measures: Relative risk of occurrence of suicidal behaviors during follow-up intervals by status of smoking and psychiatric disorders at the start of the interval, estimated by generalized estimating equations with repeated measures. The National Institute of Mental Health Diagnostic Interview Schedule was used at baseline and at each reassessment.
Results: Current daily smoking, but not past smoking, predicted the subsequent occurrence of suicidal thoughts or attempt, independent of prior depression and substance use disorders (adjusted odds ratio, 1.82; 95% confidence interval, 1.22-2.69). Additionally, current daily smoking, but not past smoking, predicted the subsequent occurrence of suicidal thoughts or attempt, adjusting for suicidal predisposition, indicated by prior suicidality, and controlling for prior psychiatric disorders (adjusted odds ratio, 1.74; 95% confidence interval, 1.17-2.54).
Conclusions: The biological explanation of the finding that current smoking is associated with subsequent suicidal behavior is unclear. Recent observations of lower monoamine oxidase activity (which may play a role in central nervous system serotonin metabolism) in current smokers but not ex-smokers might provide clues, but interpretations should proceed cautiously.