BACKGROUND

Asthma affects more than 17 million people in the United States;1/3 of these are children. Children are particularly vulnerable to airborne pollution because of their narrower airways and because they generally breathe more air per pound of body weight than adults, increasing their exposure to air pollutants. However, the results from previous studies on the association between motor vehicle emissions and the development of childhood wheeze and asthma are conflicting. Therefore, we conducted a meta-analysis to clarify their potential relationship.

METHODS

MEDLINE, Highwire, and The Cochrane Library databases were searched for relevant studies. Adjusted odds ratio (OR) with corresponding 95% confidence interval (CI) for the association between traffic air pollutants and wheeze or asthma were retrieved from individual studies and pooled to generate summary effect estimates (meta-OR) in STATA 11.1.

RESULTS

Nineteen studies were included in the meta-analysis. Exposure to nitrogen dioxide (meta-OR: 1.05, 95% CI: 1.00-1.11), nitrous oxide (meta-OR: 1.02, 95% CI: 1.00-1.04), and carbon monoxide (meta-OR: 1.06, 95% CI: 1.01-1.12) were positively associated with a higher prevalence of childhood asthma. Exposure to sulfur dioxide (meta-OR: 1.04, 95% CI: 1.01-1.07) was positively associated with a higher prevalence of wheeze in children. Exposure to nitrogen dioxide was positively associated with a higher incidence of childhood asthma (meta-OR: 1.14, 95% CI: 1.06-1.24), and exposures to particulate matter was positively associated with a higher incidence of wheeze in children (meta-OR: 1.05, 95% CI: 1.04-1.07).

CONCLUSIONS

Living or attending schools near high traffic density roads exposes children to higher levels of motor vehicle air pollutants, and increases the incidence and prevalence of childhood asthma and wheeze.