Source
Christchurch Health and Development Study, University of Otago, Christchurch School of Medicine and Health Sciences, PO Box 4345, Christchurch, New Zealand.
Abstract
BACKGROUND:
Research on the comorbidity between cigarette smoking and major depression has not elucidated the pathways by which smoking is associated with depression.
AIMS:
To examine the causal relationships between smoking and depression via fixed-effects regression and structural equation modelling.
METHOD:
Data were gathered on nicotine-dependence symptoms and depressive symptoms in early adulthood using a birth cohort of over 1000 individuals.
RESULTS:
Adjustment for confounding factors revealed persistent significant (P<0.05) associations between nicotine-dependence symptoms and depressive symptoms. Structural equation modelling suggested that the best-fitting causal model was one in which nicotine dependence led to increased risk of depression. The findings suggest that the comorbidity between smoking and depression arises from two routes; the first involving common or correlated risk factors and the second a direct path in which smoking increases the risk of depression.
CONCLUSIONS:
This evidence is consistent with the conclusion that there is a cause and effect relationship between smoking and depression in which cigarette smoking increases the risk of symptoms of depression.