Findings of a study led by the Barcelona Institute for Global Health (ISGlobal) and published in the European Respiratory Journal suggest that a significant proportion of childhood asthma cases may be attributable to outdoor air pollution, and that these cases could be prevented.

Asthma is the most common chronic disease in children. Emerging evidence suggests that exposure to air pollution may increase the risk of developing this respiratory disease during childhood. The new study has estimated the burden of childhood asthma in 18 European countries that may be attributable to outdoor NO₂, PM_2.5 and black carbon (BC).

The researchers combined country-level childhood incidence rates and pooled exposure-response functions with counts and exposure estimates for more than 63 million children.

They investigated two exposure reduction scenarios: first, the recommended annual World Health Organization (WHO) air quality guideline values; and second, the minimum air pollution levels recorded across 41 studies in the underlying meta-analysis.

NO₂ ranged from 1.4 to 70.0 µg·m⁻³, with a mean of 11.8 µg·m⁻³. PM^2.5 ranged from 2.0 to 41.1 µg·m⁻³, with a mean of 11.6 µg·m⁻³. BC ranged from 0.003 to 3.7×10⁻⁵m⁻¹, with a mean of 1.0×10⁻⁵m⁻¹.

Compliance with the NO₂ and PM_2.5 WHO guidelines, respectively, was estimated to prevent 2,434 (0.4%) and 66,567 (11%) incident cases.

Meeting the minimum air pollution levels for NO₂ (1.5 µg·m⁻³), PM_2.5 (0.4 µg·m⁻³) and BC (0.4×10⁻⁵m−¹), respectively, was estimated to prevent 135,257 (23%), 191,883 (33%) and 89,191 (15%) incident cases.

Overall, these estimates are in line with two previous studies conducted in the UK which found that the percentage of annual incident childhood asthma attributable to NO₂ was 22%. Another study estimated that 4 million new pediatric asthma cases could be attributable to NO₂ pollution annually, 64% of which occur in urban centers.

Only in the past two years, several analyses on air pollution and onset of childhood asthma have emerged, strengthening the case from different research teams that air pollution is contributing substantially to the burden of pediatric asthma. Largely, these impacts are preventable and there are numerous policy measures which can reduce the ambient levels of, and children's exposures to, outdoor air pollution. We can and should do something about it.

—Haneen Khreis, lead author of the study and an associated researcher at the Center for Advancing Research in Transportation Emissions, Energy, and Health at the Texas A&M Transportation Institute

The 18 European countries covered in the study are Austria, Belgium, Denmark, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Lithuania, the Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom. Countries from Eastern Europe were not included due to the lack of air pollution exposure data in the region.

Resources

• Haneen Khreis, Marta Cirach, Natalie Mueller, Kees de Hoogh, Gerard Hoek, Mark J. Nieuwenhuijsen, David Rojas-Rueda (2019) “Outdoor Air Pollution and the Burden of Childhood Asthma across Europe” European Respiratory Journal doi: 10.1183/13993003.02194-2018