Relationship between smoking experience and risk of suicide mortality in South Korean adults: A nationwide population-based retrospective cohort study

Background: Korea has one of the highest suicide rates in the world. Many factors associated with suicidal thoughts or behaviors are known. This study examines the association between 1) smoking status or intensity (pack-years) and 2) risk of suicide mortality in South Korea. Methods: We analyzed data from 3,966,305 individuals aged ≥20 who underwent health examinations conducted by the South Korean National Health Insurance Service in 2009 and were followed until December 2021. Participants were categorized based on their baseline smoking status and intensity. We performed a Multivariate Cox proportional hazards regression analysis with subgroup analysis by age, sex, body mass index, alcohol consumption, regular exercise, and depression. Results: During an 11.1-year follow-up period, 12,326 individuals died by suicide. Compared with never-smokers, increased hazard ratios of suicide mortality were observed in current smokers (1.64, 95 % CI = 1.56–1.72), but not in ex-smokers. The suicide mortality risk of current smokers increased for all types of smoking intensity without a dose–response relationship. The association between smoking and suicide mortality risk was stronger among women, non-drinkers, adults aged <40 years, non-obese patients, and individuals without depression. Limitation: Given that the study used retrospective data, the causal relationship remains unclear. Conclusion: Current smoking is associated with a significant increased risk of suicide mortality. Smoking cessation is crucial to prevent suicide, especially among young adults, non-obese individuals, non-drinkers, women, and those without depression. Government policies in South Korea should focus on raising awareness about smoking hazards and providing cessation education to reduce the suicide mortality.