Exposure to traffic-related air pollution increases the risk of developing childhood asthma

Children and adolescents exposed to high levels of traffic-related air pollution have a higher risk of developing asthma, according to a systematic review and large-scale analysis performed by researchers from the Barcelona Institute for Global Health (ISGlobal) and the University of Leeds.

An estimated 334 million people suffer from asthma worldwide, and numerous studies show that the prevalence of childhood asthma has markedly increased since the 1950s. The factors underlying this increase are largely unknown, but changes in environmental exposures including air pollution are thought to be involved.

This study, published in Environment International, is the largest and most up-to-date review and analysis of current evidence of exposure to traffic-related air pollution (TRAP) and development of childhood asthma. The authors reviewed more than 4,000 articles published on the topic between 1999 and September 2016, and analysed the data from 41 epidemiological studies from the Netherlands, the USA, Canada, Germany, Norway, Sweden, England, France, Italy, Japan, China, Taiwan, and Korea, that met criteria for inclusion in the systematic review. Khreis and co-authors then combined data for over a million kids in meta-analyses, and showed that TRAP exposures increase the risk of childhood asthma development.

Haneen Khreis, researcher at the University of Leeds and lead author of the study, concludes that “according to the analysis we performed, combining data from multiple studies, we can now confirm that there is a positive association between TRAP exposures and development of childhood asthma”. In particular, the review looked at exposure to traffic-associated nitrogen dioxide, black carbon, and particulate matter (PM2.5 and PM10) during childhood, and the subsequent development of asthma. “Our analysis shows that the most robust effects were in association with black carbon exposures, a specific marker of traffic exhaust and a diesel-related pollutant, but more research is needed to draw definitive conclusions, including exploring the effects of non-exhaust pollutants”. Many cities in Europe nowadays are diesel dominated, and there is an urgent need to reduce their emissions.

“Air pollution has a great impact on childhood health” underlines Mark Nieuwenhuijsen, senior author of the study and director of the Urban Planning, Environment and Health Initiative at ISGlobal. “Given that almost 70% of people globally are projected to live in urban areas by 2050, exposure to traffic-related air pollution is a major global health problem and we need to act quickly”, he adds.