Tore Tjora

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. Cross-sectional and longitudinal analyses of the smoking-depression association from adolescence to adulthood. Hordaland, Norway. 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. Daily smoking and depressed mood were measured in each wave. 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). 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.

Aims: Adolescence is considered a critical phase for smoking initiation, while smoking initiation in adulthood has received less attention. In the present study, we investigated smoking initiation in early adulthood, with an additional focus on how socioeconomic status (SES) relates to late-onset smoking. Methods: The Norwegian Longitudinal Health Behaviour Study followed a representative sample of adolescents (n=530) from age 13 (7th grade) to age 30 (years 1990–2007) through 9 waves of data collection. Information was collected on the adolescents’ gender, smoking, alcohol use, cannabis use, physical activity, and SES. Those reporting to be smokers at age 30, but not at age 18, were defined as “late-onset smokers”. Results: At age 30, 21% were daily smokers, of which 45% met our definition of late-onset smoking. Participants with a low SES had a higher odds ratio for late-onset smoking (OR=3.42) and a lower odds ratio for quitting smoking (OR=0.40) after adjusting for confounders. Conclusions: Early adulthood is an additional critical phase for daily smoking initiation. The clear and consistent negative association between SES and late-onset smoking, as well as the positive association between SES and smoking cessation, contribute to the association between SES and smoking in the general adult population.

Studies on adolescent smoking indicate that the smoking behaviours of their parents, siblings and friends are significant micro-level predictors. Parents' socioeconomic status (SES) is an important macro-level predictor. We examined the longitudinal relationships between these predictors and the initiation and development of adolescents' smoking behaviour in Norway.