Risk of depressive disorders after tobacco smoking cessation: a retrospective cohort study in Fukuoka, Japan

Objective We sought to examine the effect of smoking cessation on subsequent development of depressive disorders. Design This was a retrospective cohort study. Methods We used administrative claim and health check data from fiscal years 2010 to 2014, obtained from the largest health insurance association in Fukuoka, Japan. Study participants were between 30 and 69 years old. The end-point outcome was incidence of depressive disorders. Survival analysis and Cox proportional hazards models were conducted. The evaluated potential confounders were sex, age, standard monthly income and psychiatric medical history. Results The final number of participants was 87 255, with 7841 in the smoking cessation group and 79 414 in the smoking group. The result of survival analysis showed no significant difference in depressive disorders between the two groups. The results of Cox proportional hazards models showed no significant difference by multivariate analysis between participants, including users of smoking cessation medication (HR 1.04, 95% Cl 0.89 to 1.22) and excluding medication use (HR 0.97, 95% Cl 0.82 to 1.15). Conclusions The present study showed that there were no significant differences with respect to having depressive disorders between smoking cessation and smoking groups. We also showed that smoking cessation was not related to incidence of depressive disorders among participants, including and excluding users of smoking cessation medication, after adjusting for potential confounders. Although the results have some limitations because of the nature of the study design, our findings will provide helpful information to smokers, health professionals and policy makers for improving smoking cessation.