title: A systematic review of longitudinal studies on the association between depression and smoking in adolescents.
abstract: BACKGROUND
  It is well-established that smoking and depression are associated in adolescents, but the temporal ordering of the association is subject to debate.
  
  
  METHODS
  Longitudinal studies in English language which reported the onset of smoking on depression in non clinical populations (age 13-19) published between January 1990 and July 2008 were selected from PubMed, OVID, and PsychInfo databases. Study characteristics were extracted. Meta-analytic pooling procedures with random effects were used.
  
  
  RESULTS
  Fifteen studies were retained for analysis. The pooled estimate for smoking predicting depression in 6 studies was 1.73 (95% CI: 1.32, 2.40; p < 0.001). The pooled estimate for depression predicting smoking in 12 studies was 1.41 (95% CI: 1.21, 1.63; p < 0.001). Studies that used clinical measures of depression were more likely to report a bidirectional effect, with a stronger effect of depression predicting smoking.
  
  
  CONCLUSIONS
  Evidence from longitudinal studies suggests that the association between smoking and depression is bidirectional. To better estimate these effects, future research should consider the potential utility of: (a) shorter intervals between surveys with longer follow-up time, (b) more accurate measurement of depression, and (c) adequate control of confounding.
authors.affiliation: Dalla Lana School of Public Health, University of Toronto, Toronto, Canada. michael.chaiton@utoronto.ca
authors.forename: Michael O
authors.initials: MO
authors.lastname: Chaiton
authors.forename: Joanna E
authors.initials: JE
authors.lastname: Cohen
authors.forename: Jennifer
authors.initials: J
authors.lastname: O'Loughlin
authors.forename: Jurgen
authors.initials: J
authors.lastname: Rehm
mesh_terms: D000293:Adolescent; D015897:Comorbidity; D003863:Depression / Q000150:complications*; D018450:Disease Progression; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D012907:Smoking / Q000009:adverse effects*; D055815:Young Adult