Tobacco smoking as a risk factor for major depressive disorder: population-based study

Background
Smoking is disproportionately prevalent among people with
psychiatric illness.

Aims
To investigate smoking as a risk factor for major depressive disorder.

Method
A population-based sample of women was studied using case–control and retrospective cohort study designs.
Exposure to smoking was self-reported, and major
depressive disorder diagnosed using the Structured Clinical
Interview for DSM–IV–TR (SCID–I/NP).

Results
Among 165 people with major depressive disorder and 806 controls, smoking was associated with increased odds for major depressive disorder (age-adjusted odds ratio (OR)=1.46, 95% CI 1.03–2.07). Compared with non-smokers, odds for major depressive disorder more than doubled for heavy smokers (>20 cigarettes/day). Among 671 women with no history of major depressive disorder at baseline, 13 of 87
smokers and 38 of 584 non-smokers developed de novo major depressive disorder during a decade of follow-up. Smoking increased major depressive disorder risk by 93% (hazard ratio (HR)=1.93, 95% CI 1.02–3.69); this was not explained by physical activity or alcohol consumption.

Conclusions
Evidence from cross-sectional and longitudinal data suggests that smoking increases the risk of major depressive disorder in women.