Smoking cessation and depression risk in newly diagnosed COPD patients: A nationwide cohort study

Depression is a common and clinically significant comorbidity in chronic obstructive pulmonary disease (COPD), adversely influencing prognosis and survival. Although smoking cessation improves mental health in the general population, its effect on depression risk after a new COPD diagnosis remains uncertain.

Using the National Health Insurance Service-National Health Screening Cohort, we conducted a nationwide population based cohort study of 5671 adults newly diagnosed with COPD between 2003 and 2014. Smoking status before and after diagnosis was classified as continual smokers, short term quitters (<2 years), long term quitters (≥2 years), and never smokers. Incident depression was defined using ICD 10 codes F32-F33 with antidepressant prescriptions. Cox proportional hazards models estimated adjusted hazard ratios (aHRs) for depression.

Over 48,621 person years of follow up, 603 incident depression cases occurred. Long term quitters showed a significantly lower risk of depression compared with continual smokers (aHR 0.66; 95% CI 0.45-0.97). The association was strongest among patients with severe COPD (aHR 0.40; 95% CI 0.20-0.82) and was consistently observed in subgroups defined by male sex, age under 65 years, lower comorbidity burden, higher household income, and body mass index below 25 kg/m².

In this nationwide cohort of newly diagnosed COPD patients, sustained smoking cessation was associated with a substantially reduced risk of subsequent depression, particularly in those with severe disease. These findings support emphasizing long term smoking cessation as a core element of comprehensive COPD management to improve both mental health and overall outcomes in routine clinical practice worldwide settings.