Persistent heavy smoking as risk factor for major depression (MD) incidence--evidence from a longitudinal Canadian cohort of the National Population Health Survey.
Reports of bidirectional associations between smoking and major depression (MD) have been interpreted as providing evidence for confounding by shared-vulnerability factors (SV) that predispose individuals to both conditions. If this is true, then smoking cessation may not reduce the risk of MD. From clinical practice and public health perspectives, the long-term outcomes associated with smoking persistence and cessation are potentially important and deserve exploration. To this end, the 12-year risk of MD in persistent heavy smokers and abstainers who were former-heavy smokers with and without adjustment for potential confounders were compared.
Follow-up data from the National Population Health Survey (NPHS) was used. Multinomial logistic (ML) models were fit to identify potential confounders. Using proportional hazard (PH) models, unadjusted and adjusted hazard ratios (HRs) for MD outcome were estimated for different smoking patterns.
The unadjusted HR relating the risk of MD among current-heavy versus former-heavy smokers was 4.3 (95% CI: 2.6-6.9, p