Parental tobacco and indoor secondhand smoking exposure and the risk of offspring under-five mortality in low- and middle-income countries.

Children are vulnerable to exposure of secondhand smoking (SHS) which is a major preventable cause of disease and death. This study aimed to investigate the association between parental tobacco use or SHS exposure, respectively, and under-five mortality. Data were obtained from the nationally representative and population-based Demographic and Health Surveys in low- and middle-income countries (LMICs) between 2000 and 2018. Cox proportional hazard regression models with complex survey design were conducted to examine the adjusted associations between parental smoking and SHS exposure and child under-five mortality. In the pooled analysis of parental smoking, 437 322 children were included. Compared with children whose parents are not smoking, those whose father or both parents smoked any form of tobacco had higher risks of mortality (hazard ratio [HR] = 1.08, 95% confidence interval [CI] = 1.03-1.13; HR = 1.18, 95% CI = 1.06-1.32, respectively). In addition, parental using smokeless tobacco, smoking tobacco, and using smokeless tobacco and smoking tobacco simultaneously was significantly associated with child under-five mortality (HR = 1.07, 95% CI = 1.01-1.12; HR = 1.12, 95%CI = 1.04-1.21; and HR = 1.17, 95%CI = 1.06-1.30, respectively). In the pooled analysis of SHS exposure, 605 442 children were included, and weekly and daily SHS exposure were significantly associated with child under-five mortality (HR = 1.11, 95% CI = 1.03-1.20, and HR = 1.10, 95% CI = 1.06-1.15, respectively). The results were robust in most stratification analyses and sensitivity analyses. Parental tobacco use and indoor SHS exposure were associated with increased risk of under-five mortality in LMICs. Comprehensive tobacco control programs should be considered by policymakers in LMICs to promote smoke-free environments for children.