Secondhand smoke exposure and depressive symptoms in children: a longitudinal study

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-11th grade (2005-11) in 5 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% CI) = 0.041 (0.017, 0.068) for home exposure; 0.057 (0.030, 0.084) for car exposure). In longitudinal analyses from 5th to 6th grade, B (95% CI), adjusted for demographics and baseline depressive symptoms, was 0.042 (0.003, 0.080) for home exposure and 0.061 (0.019, 0.103) for car exposure. From 6th to 7th grade, B (95% CI) was 0.057 (0.003, 0.110) for home exposure and 0.074 (0.015, 0.133) for car exposure. SHS exposure at any age did not predict depressive symptoms two years later. Conclusions: SHS exposure is associated with depressive symptoms in young persons, both concurrently and one year later. This finding adds to the evidence base supporting that children should be protected from SHS exposure.