Traffic-related organic and inorganic air pollution and risk of development of childhood asthma: A meta-analysis.

The effect of early childhood exposure to traffic-related air pollution (TRAP) on the development of asthma remains unclear. The aim of this study was to clarify potential associations between TRAP (fine particulate matter, PM2.5; nitrogen dioxide, NO2; Benzene and total volatile organic pollutants, TVOCs) and childhood asthma by integrating the results from previous studies. Elsevier, LISTA (EBSCO) and Web of Science databases were searched for relevant studies. Adjusted odds ratio (OR) with corresponding 95% confidence interval (CI) for the association between traffic-related air pollutants and health effects were recovered from individual studies and summary effect estimates (meta-OR) were generated in Review Manager 5.3. Twenty-seven studies were included in the meta-analysis and the results showed that TRAP increased the risk of asthma among children: PM2.5 (meta-OR = 1.07, 95% CI:1.00-1.13), NO2 (meta-OR = 1.11, 95% CI:1.06-1.17), Benzene (meta-OR: 1.21, 95% CI:1.13-1.29) and TVOC (meta-OR:1.06, 95% CI: 1.03-1.10). Sensitivity analyses supported these findings. In addition, regional analysis showed that ORs of inorganic TRAP (PM2.5 and NO2) on the risk of childhood asthma were significantly higher in Asia than those in Europe and North America. Subsequent research should focus on the association between organic pollutants in TRAP and childhood asthma. Furthermore, the disentanglement between TRAP and other pollutant sources may be investigated in future studies.