The association of smoking and depression is established, but it remains unclear which depression dimensions are linked to smoking patterns.
The associations between smoking and depression dimensions were investigated among 4,980 male and 5,997 female Finnish twins. Longitudinal cigarette smoking patterns in 1975-1981 included multiple categories describing consistency and change. Depression was measured with the Beck Depression Inventory (BDI) in 1990. Preexisting depressed mood was screened with the life satisfaction scale strongly correlated with BDI. The BDI dimensions were negative attitudes toward self (NATS), performance impairment (PI), and weight loss (WL). Multiple logistic regressions and conditional logistic regressions for discordant twin pairs were conducted.
Controlling for confounders, two smoking patterns predicted all later depression dimensions. The NATS dimension showed a significant Sex × Smoking interaction: the associations of persistent smoking (odds ratio = 1.6, 95% CI = 1.3-2.0; p