Second-hand smoking and obesity among non-smoking adolescents aged 12-15 years from 38 low- and middle-income countries

Introduction: Second-hand smoking (SHS) may be a risk factor for obesity in adolescence but data on the association between SHS and obesity are scarce, especially from low- and middle-income countries (LMICs). Therefore, the aim of this study was to assess the association between SHS and obesity among adolescents aged 12-15 years from 38 LMICs. Methods: Cross-sectional data from 38 LMICs that participated in the Global School-based Student Health Survey (GSHS) were analyzed. Body mass index was calculated based on measured weight and height. The 2007 WHO Child Growth reference was used to define obesity. SHS was categorized as no exposure, non-daily exposure (i.e., 1-6 days), and daily exposure (i.e., 7 days) based on the number of days exposed to second-hand smoke in the past 7 days. Multivariable logistic regression and meta-analyses were conducted to assess the associations. Results: The analyzed sample consisted of 88,209 adolescents aged 12-15 years who never smoked. The overall prevalence of non-daily and daily SHS was 34.2% and 15.7%, respectively. After adjustment for potential confounders, compared with no SHS, there was no significant association between non-daily SHS and obesity (OR=0.94; 95%CI=0.86-1.02) but adolescents who reported daily SHS were significantly more likely to have obesity (OR=1.19; 95%CI=1.06-1.34). Conclusions: The prevalence of SHS was high among adolescents in LMICs and daily SHS was associated with a significant increase in odds of obesity. Future studies with longitudinal designs are warranted to assess causality and whether prevention of SHS can reduce risk of obesity in adolescence