Depressive symptoms among patients with COPD according to smoking status: a Danish nationwide case–control study of 21 184 patients

INTRODUCTION: Depressive symptoms appear more often among patients with COPD and are associated with reduced disease control and increased mortality. Both smoking and COPD increase the risk of depressive symptoms. Whether smoking cessation among COPD patients affects the occurrence of depressive symptoms is unknown. We hypothesised that smoking cessation in patients with COPD leads to reduced use of antidepressants and fewer admissions to psychiatric hospitals with depression, anxiety or bipolar disorder. METHODS: We conducted a nationwide retrospective case–control study, in patients from The Danish Register for COPD with spirometry-verified COPD, age ≥40 years, a history of smoking and absence of cancer. Consistent smokers were matched 1:1 with ex-smokers using a propensity score model. Prescription fillings of antidepressants and risk of admissions to psychiatric hospitals with either depression, anxiety or bipolar disorder both descriptively was assessed by Cox proportional hazard models. RESULTS: We included 21 184 patients. A total of 2011 consistent smokers collected antidepressant prescriptions compared with 1821 ex-smokers. Consistent smoking was associated with increased risk of filling prescription on antidepressants (HR 1.4, 95% CI 1.3–1.5, p<0.0001) and with increased risk of psychiatric hospital admission with either depression, anxiety or bipolar disorder (HR 2.0, 95% CI 1.6–2.5). The associations persisted after adjustment for former use of antidepressants. CONCLUSION: Consistent smoking among COPD patients was associated with increased use of antidepressants and admissions to psychiatric hospitals with either depression, anxiety or bipolar disorder, compared to smoking cessation.