Second-hand smoking and depressive symptoms among in-school adolescents

Introduction: Smoking has been linked with depressive symptoms in adolescents but data on second-hand smoking (SHS) and depressive symptoms in low- and middle-income countries (LMICs) are scarce. Thus, the aim of this study was to analyze the association between SHS and depressive symptoms among in-school adolescents from 22 LMICs. Methods: Data from the Global School-based Student Health Survey (GSHS) 2003-2008 were analyzed in June 2019. Data on past-week exposure to second-hand smoke and past-year depressive symptoms were collected. The association between SHS and depressive symptoms was studied using multivariable logistic regressions and meta-analyses. Results: The sample consisted of 37,505 adolescents aged 12-15 years who never smoked. The prevalence of depressive symptoms increased from 23.0% in adolescents with no SHS to 28.9% in those with SHS everyday in the past week. After adjusting for sex, age, food insecurity, and country, there was a dose-response relationship between SHS and depressive symptoms in the overall sample [0 day: reference; 1-2 days: OR=1.06 (95%CI=0.95-1.18); 3-6 days: OR=1.38 (95%CI=1.20-1.58); 7 days: OR=1.63 (95%CI=1.44-1.86)]. Finally, the country-wise analysis showed that SHS on at least 3 days (vs. <3 days) in the past week was associated with a 1.48-fold increase in the odds of depressive symptoms (95%CI=1.39-1.59), with a low level of between-country heterogeneity (I2=4.2%). Conclusions: There was a positive association between SHS and depressive symptoms among in-school adolescents from LMICs. Further research should investigate causality and assess whether prevention of exposure to second-hand smoke can have a positive effect on the mental well-being of adolescents.