Interaction of smoking and depression or anxiety on the mortality of COPD patients: a prospective study

Background: Smoking, depression, and anxiety increase the risk of death in chronic obstructive pulmonary disease (COPD), but the combined effect of these factors is unknown. This study aimed to assess the interactive effects of smoking and psychological disorders on the death of patients with COPD.

Study Design: A cohort study which enrolled 7,787 participants in 14 rural communities was observed from May, 2008 to May, 2012.

Methods: Prospective data for 7,787 Chinese patients with COPD were analyzed. The product of smoking and psychological disorders was added to the logistic regression model to evaluate the multiplicative interaction and relative excess risk of interaction (RERI). The attributable proportion (AP) of interaction and the synergy index (S) was applied to evaluate the additive interaction of two factors.

Results: In COPD patients, the interaction of current smoking and depressive symptoms increased death risk by 3.8-fold (OR 3.78 [95% CI 2.51-5.05]) with significant biological interactions (RERI 1.74 [0.51 –2.99]; AP 0.48 [0.13–0.85]; S 2.98 [1.44-4.56]). The biological interactions increased with increasing years or pack-years of smoking (years of smoking ≥ 30: RERI 1.80 [1.05–2.75]; AP 0.48 [0.15–0.82]; S 2.85[1.75–3.96]. pack-years of smoking ≥ 40: RERI 3.11 [1.54–4.71]; AP 0.60 [0.31–0.91]; S 4.00[2.84–5.26].). Similarly, the combined effect of current smoking and anxious symptoms increased death risk by 4.3-fold (OR 4.27[95% CI 2.96-5.59]) with significant biological interactions (RERI 1.51 [0.31 –2.74]; AP 0.46 [0.11–0.87]; S 2.89 [1.31-4.51]). The biological interactions also increased with increasing years or pack-years of smoking (years of smoking ≥ 30: RERI 1.41 [0.45–2.43]; AP 0.45 [0.12–0.81]; S 2.88[1.24–5.98]. pack-years of smoking ≥ 40: RERI 3.15 [2.07–4.61]; AP 0.55 [0.21– 0.94]; S 3.00[1.45–4.75].).

Conclusions: Smoking and psychological distress are associated with risk of death in patients with COPD. The risk for death and psychological distress increases with increasing duration of smoking (years) and cigarette pack-years.

Clinical Trial registration: Chinese Clinical Trials Registration (ChiCTR-TRC-12001958).