The association between smoking and depression from adolescence to adulthood

Background and aims: The association between depression and smoking is firmly established, but how the association develops remains unclear. The aim of this study was to examine development of the smoking-depression association from early adolescence to adulthood.

Design: Cross-sectional and longitudinal analyses of the smoking-depression association from adolescence to adulthood.

Setting: Hordaland, Norway.

Participants: A cohort of adolescents (initially, 924 pupils) in the Norwegian Longitudinal Health Behaviour Study (NLHB) was followed over nine data collection waves from ages 13 to 30 years.

Measurements: Daily smoking and depressed mood were measured in each wave.

Findings: In the cross-sectional analyses, daily smoking and depression were significantly associated (P-value range from P < 0.01 to 0.04) in eight of nine waves. In the final longitudinal model, after controlling for the time-invariant effects of smoking and depression and of tertiary factors, the only significant paths were early adolescent smoking prediction of early adolescent depression (waves 1-2: β = 0.07, P < 0.05; waves 2-3: β = 0.12, P < 0.05) and vice versa (waves 1-2: β = 0.10, P < 0.05; waves 2-3: β = 0.08, P < 0.05).

Conclusions: The inter-relationship between depression and smoking seems to be due to the reciprocal causal effects between smoking and depression that are established in early adolescence and maintained into adulthood.