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Introduction: We examined the mediating role of friends smoking in the association between depressive symptoms and daily/weekly cigarette smoking from adolescence into adulthood.Methods: Data were drawn from the Nicotine Dependence In Teens study (NDIT, Canada) and the Avon Longitudinal Study of Parents and Children (ALSPAC, UK) studies. Three age groups were investigated in NDIT: age 13-14 (n = 1189), 15-16 (n = 1107), and 17-18 (n = 1075), and one in ALSPAC (n = 4482, age 18-21). Multivariable mediation models decomposed the total effect (TE) of depressive symptoms on smoking into a natural direct effect (NDE) and natural indirect effect (NIE) through friends smoking.Results: The odds ratios (ORs) for the TE were relatively constant over time with estimates ranging from 1.12 to 1.35. Friends smoking mediated the association between depressive symptoms and smoking in the two youngest samples (OR [95% confidence interval [CI] 1.09 [1.01,1.17] in 13- to 14-year-olds; 1.10 [1.03,1.18] in 15- to 16-year-olds). In the two older samples, NDE of depressive symptoms was close to the TE, suggestive that mediation was absent or too small to detect.Conclusion: Friends smoking mediates the association between depressive symptoms and daily/weekly cigarette smoking in young adolescents.Implications: If young adolescents use cigarettes to self-medicate depressive symptoms, then interventions targeting smoking that ignore depressive symptoms may be ineffective. Our results also underscore the importance of the influence of friends in younger adolescents, suggestive that preventive intervention should target the social environment, including social relationships. [ABSTRACT FROM AUTHOR]

Introduction: We investigated whether secondhand smoke (SHS) exposure is associated with depressive symptoms in a population-based sample of children.Methods: Never-smoking students from 29 French-language elementary schools in Greater Montréal, Canada, were followed from 5th to 11th grade (2005-2011) in five waves: 1 (5th grade), 2 (spring 6th grade), 3 (7th grade), 4 (9th grade), and 5 (11th grade). Associations between depressive symptoms and SHS exposure at home and in cars were examined in cross-sectional and longitudinal gamma generalized regression models adjusted for sex, maternal education, and neighborhood socioeconomic status.Results: The sample comprised 1553 baseline never-smokers (mean [SD] age = 10.7 [0.5] years; 44% male; 89% French-speaking). SHS exposure at home and in cars was associated with higher depressive symptom scores in cross-sectional analyses pooled across grades and adjusted for demographics (B [95% confidence interval (CI)] = 0.041 [0.017 to 0.068] for home exposure; 0.057 [0.030 to 0.084] for car exposure). In longitudinal analyses from fifth to sixth grade, B (95% CI), adjusted for demographics and baseline depressive symptoms, was 0.042 (0.003 to 0.080) for home exposure and 0.061 (0.019 to 0.103) for car exposure. From sixth to seventh grade, B (95% CI) was 0.057 (0.003 to 0.110) for home exposure and 0.074 (0.015 to 0.133) for car exposure. SHS exposure at any age did not predict depressive symptoms 2 years later.Conclusions: SHS exposure is associated with depressive symptoms in young persons, both concurrently and 1 year later. This finding adds to the evidence base supporting that children should be protected from SHS exposure.Implications: SHS exposure has deleterious effects on physical health and results of this study raise concerns that such exposure might also affect the mental health of young persons. Clearly, protecting children from SHS in all locations is a critical public health priority. Although research is needed to determine if the association between SHS exposure and depressive symptoms is causal, continued implementation of smoking bans and educational efforts to discourage smoking in vehicles when children are present are warranted. [ABSTRACT FROM AUTHOR]