Smoking, Nicotine Dependence, and Suicide Risk: A Dose-Response Analysis Using the Heavy Smoking Index.

OBJECTIVES: Although smoking is a risk factor for suicide, the role of nicotine dependence is unclear. We evaluated whether the Heavy Smoking Index (HSI) could serve as a brief screening tool to identify Korean adults at elevated risk of suicidal ideation, suicide planning, and suicide attempts in population health settings. METHODS: We analyzed data from the 2019 and 2022 Korea National Health and Nutrition Examination Survey using multivariable logistic regression to estimate adjusted odds ratios (AORs) for suicidal ideation, suicide planning, and suicide attempts by smoking status and HSI-defined nicotine dependence. RESULTS: Among 9321 participants aged ≥19 years, 4.7% reported suicidal ideation, 1.1% had a suicide plan, and 0.5% had attempted suicide. Compared with nonsmokers, smokers had higher odds of suicidal ideation (AOR = 1.75; 95% CI, 1.33-2.31) and suicide planning (AOR = 3.33; 95% CI, 1.99-5.58); the odds of suicide attempts were not significantly higher (AOR = 1.17; 95% CI, 0.53-2.59). Among current smokers, higher HSI-defined nicotine dependence was associated with greater risk of suicidal ideation and suicidal planning, consistent with a dose-response relationship across dependence levels. CONCLUSIONS: Nicotine dependence influenced suicidal behaviors beyond smoking status alone, supporting the integration of targeted cessation programs into national suicide prevention frameworks. Future longitudinal studies with biochemical assessment should clarify the underlying causal pathways.