Secondhand Smoke and Traffic Exhaust Confer Opposing Risks for Asthma in Normal and Overweight Children

Objective: Exposure to ultrafine particles (UFP) in secondhand smoke (SHS) and traffic-related air pollution (TRAP) may elicit chronic inflammation. It was hypothesized that the association between these exposures would be potentiated in overweight versus normal-weight children. Methods: Average lifetime exposure to TRAP and SHS and objective, physician-diagnosed asthma were determined for 575 children at age 7. Overweight was defined as having a body mass index (BMI) >85th percentile for age and gender. The association between TRAP and SHS exposure and asthma was examined by logistic regression stratified by BMI. Results: A total of 131 children were overweight; the prevalence of asthma was 24.4% and 14.2% among overweight and normal-weight children, respectively. Exposure to SHS was significantly associated with asthma among overweight (adjusted odds ratio [adjOR]=3.0; 95% confidence interval [CI]=1.2, 7.4) but not normal-weight children (adjOR=1.1; 95% CI=0.4, 2.7). In contrast, TRAP was significantly associated with asthma among normal-weight (adjOR=1.8; 95% CI=1.0, 3.4) but not overweight children (adjOR=0.7; 95% CI=0.4, 2.7). Conclusions: The association between SHS and TRAP exposure and asthma is modified by children's weight. Children's time-activity patterns, including time spent indoors or outdoors, may vary by weight and play an important role in these UFP exposures.