Background: We examined the effects of smoking habit change on the risk of depression using the National Health Insurance Service-National Health Screening Cohort database of Korea. Methods: This nationwide population-based cohort study included 88,931 men aged 40 years or older. The participants were divided into baseline heavy (≥20 cigarettes/day), moderate (10–19 cigarettes/day), and light (<10 cigarettes/day) smokers, quitters, and never smokers. Smokers were then categorized as continual smokers, reducers, quitters, and non-smokers based on the two-year change in smoking status between the first and second health examinations. The participants were followed from the index date to 2013 to assess depression status. Cox proportional models were used to examine the effects of smoking habit change on the risk of depression. Results: After a median 7.7 years of follow-up, 2,833 depression cases were identified. Never smokers and long-term quitters had a lower risk of depression than heavy continual smokers (hazard ratio, HR 0.817; 95% CI, confidence interval 0.689–0.967 and HR: 0.691; 95% CI: 0.559–0.853, respectively). Short-term quitters and reducers had a lower risk of depression, but it was not significant. The influence of smoking on depression was prominent among men in their 50 s (HR: 0.585; 95% CI: 0.419–0.820 in long-term quitters, HR:.0.738; 95% CI: 0.570–0.954 in never smokers). Limitations: The information about smoking habits was based on self-reported questionnaires. This study examined only men because the smoking rate among women in Korea is very low. Conclusions: This population-based study found that never smokers and long-term quitters have lower risk of depression. The risk of depression decreased when the amount of smoking decreased, but the difference was not statistically significant. Furthermore, more attention should be paid to middle-aged men when formulating smoking cessation policies.
- Long-term quitter
- National Health Insurance Service-Health Screening Cohort database
- Smoking cessation
- Smoking habit change
- Smoking reduction