Cigarette smoking and depression: tests of causal linkages using a longitudinal birth cohort.
BACKGROUND
Research on the comorbidity between cigarette smoking and major depression has not elucidated the pathways by which smoking is associated with depression.


OBJECTIVE
To examine the causal relationships between smoking and depression via fixed-effects regression and structural equation modelling.


METHODS
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.
Christchurch Health and Development Study, University of Otago, Christchurch School of Medicine and Health Sciences, PO Box 4345, Christchurch, New Zealand.
Joseph M
JM
Boden
David M
DM
Fergusson
L John
LJ
Horwood
D000293:Adolescent; D000367:Age Factors; D002648:Child; D002675:Child, Preschool; D003865:Major Depressive Disorder / Q000453:epidemiology / Q000523:psychology*; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D009520:New Zealand / Q000453:epidemiology; D012907:Smoking / Q000453:epidemiology / Q000523:psychology*; D014029:Tobacco Use Disorder / Q000453:epidemiology / Q000523:psychology*