Background: Smoking is more prevalent among people with depression. Depression may make cessation more difficult and cessation may affect depression symptoms.
Purpose: The aims of this study were to assess the associations between (1) baseline depression and 1-year smoking abstinence and (2) abstinence and change in depression.
Methods: Observational study using data collected routinely in a smoking cessation clinic in the Czech Republic from 2008 to 2014. Aim 1: N = 3775 patients; 14.3% reported mild and 15.4% moderate/severe baseline depression levels measured using Beck's Depression Inventory (BDI-II). Logistic regressions assessed if depression level predicted 1-year biochemically verified abstinence while adjusting for patient and treatment characteristics. Aim 2: N = 835 patients abstinent at 1 year; change in depression was analysed using Chi-square statistics, t test and mixed method analyses of variance.
Results: Rate of abstinence was lower for patients with mild (32.5%, OR = 0.68; 95% CI: 0.54 to 0.87, p = 0.002) and moderate/severe depression (25.8%; OR = 0.57, 95% CI: 0.45 to 0.74, p < 0.001) compared with patients without depression (40.5%). Across abstinent patients, the majority with baseline depression reported lower depression levels at follow-up. Overall mean (SD) BDI-II scores improved from 9.2 (8.6) to 5.3 (6.1); t(834) = 14.6, p < 0.001. There were significant main effects of time (F(1832) = 880.8, p < 0.001, partial η2 = 0.51) and baseline depression level (F(2832) = 666.4, p < 0.001, partial η2 = 0.62) on follow-up depression and a significant depression * time interaction (F(2832) = 296.5, p < 0.001, partial η2 = 0.42).
Conclusions: In this effective smoking cessation clinic, depression at the start of treatment predicted reduced smoking abstinence 1 year later. Patients abstinent from smoking experienced considerable improvement in depression.
Keywords: Cohort study; Depression; Effectiveness; Evidence-based practice; Preventive health services; Smoking cessation.