Rationale: Traffic-related emissions have been associated with respiratory symptoms in some studies. However, there is limited information on how traffic-related emissions relate to lung function and airway inflammation.
Objectives: To determine the differential association of traffic-related exposures with exhaled nitric oxide (NO) and lung volumes and symptoms in children with and without asthma.
Methods: We performed a longitudinal study of 200 children from ages 6 to 12 years of whom half had physician-diagnosed asthma. Two-week NO(2) and 48-hour average levels of elemental carbon and particulate matter of less than 2.5 microm (PM(2.5)) were measured at participating schools. Road and traffic densities were determined at schools and at each participant's house.
Measurements and main results: In children with asthma, an interquartile increase in road density within the 50-, 100-, and 200-m home buffer areas was associated with increased exhaled NO (50 m: 28%; P = 0.03; 95% confidence interval [CI], 3-60; 100 m: 27%; P = 0.005; 95% CI, 8-49; 200 m: 17%, P = 0.09, 95% CI, -2 to 40), and reduced FEV(1) (50 m: -0.091 L; P = 0.038; 95% CI, -0.174 to -0.007; 100 m: -0.072 L, P = -0.028, 95% CI, -0.134 to -0.009; 200 m: -0.106 L, P = 0.002, 95% CI, -0.171 to -0.041]). Exposure to NO(2) at schools was marginally associated with reduced FEV(1) (-0.020; P = 0.060; 95% CI, -0.042 to 0.001). We did not observe significant associations with PM(2.5) or elemental carbon on exhaled NO. We did not observe significant reductions in lung volumes or changes in exhaled NO among healthy children.
Conclusions: Vehicular traffic exposures are associated with increased levels of exhaled NO and reduced lung volumes in children with asthma.