Effects of progression to cigarette smoking on depressed mood in adolescents: Evidence from the National Longitudinal Study of Adolescent Health

Aims: To investigate the relationship between smoking status and continuously distributed depressed mood among a cohort of adolescents. Design: Quasi-experimental design, selecting the subset of adolescents who reported never having smoked a cigarette at baseline, some of whom progressed subsequently to smoking at follow-up approximately 1 year later. Setting: Data were drawn from the National Longitudinal Study of Adolescent Health, an ongoing study designed to assess the health status of adolescents, and explore the causes of adolescent health-related behaviours. Participants: Nationally representative sample of adolescents from the USA (n = 12 149), including a subsample who reported never having smoked a cigarette at baseline (n = 5475), aged on average 15 years at baseline and of predominantly European ancestry. Measurements: Logistic and linear regression models controlling for potential confounders to explore the relationship between smoking status and depressed mood measured using the Centers for Epidemiological Studies Depression Scale (CES-D). Findings: Various relationships between smoking status and depressed mood were observed, with a general trend for these effects to be greater among females. Smoking status at baseline did not significantly predict CES-D score at follow-up, although this effect approached significance in females (P = 0.077). Among never smokers at baseline, level of depressed mood at baseline predicted subsequent progression to smoking initiation (P = 0.022) but not progression to regular smoking (P = 0.229). Among never smokers at baseline, progression to smoking initiation during the follow-up period was associated with higher CES-D scores at follow-up, even after adjusting for baseline depressed mood (P < 0.001), with this effect greater for females than for males. Among those who initiated smoking, progression to regular smoking was associated with higher CES-D score at follow-up among females (P = 0.001), but not males (P = 0.966). Conclusions: These data appear to support a complex model of the relationship between depressed mood and smoking status which includes elements of both confounding and causal models. The relationship between cigarette smoking and depression may be a factor in the development of subsequent dependence.