Does traffic-related air pollution contribute to respiratory disease formation in children?

I n the current issue of the European Respiratory Journal, BRAUER et al. [1] report positive associations between markers of traffic-related air pollution and respiratory health outcomes, including asthma onset, incidence of wheeze, ear/nose/throat infections and serious colds or flu, in a large cohort of children 4 yrs of age. This study replicates and extends earlier findings on the same birth cohort at 2 yrs of age. Although a replication, the findings here are more compelling than the earlier study for a number of reasons. First, the effects are larger and more consistent than in the study of the children at 2 yrs of age. In the field of air pollution epidemiology, which closely links to government policy and regulation, concepts such as statistical significance take on a greater meaning, one that often goes beyond what epidemiologists and health scientists consider essential to interpreting results. The stronger and more consistent effects in the current study bolster a growing body of research suggesting that more refined exposure metrics associate with larger respiratory health effects in children, which are discussed hereafter. Secondly, and linked to the first point, the diagnostic accuracy of the conditions after the first 4 yrs of life is likely to be higher than in the first 2 yrs of life, again leading to greater confidence in the association. The relative consistency of the associations at 4 yrs of age compared with those at 2 yrs of age suggests that onset and persistence of respiratory disease formation begins at an early age and continues throughout the course of life. Thirdly, this study uses among the most sophisticated methods for exposure assessment, based on spatially and temporally representative field measurements and land use regression, capable of capturing the small area variation in traffic pollutants. Finally, this study remains one of the few population-based cohort studies operating in the world today that is capable of assessing disease incidence. Another major study, the Children’s Health Study [2] in Southern California, USA, focused on older children, aged 5–18 yrs; therefore, the study by BRAUER et al. [1] fills a gap in the literature on early onset.