Reducing nitrogen dioxide (NO2) exposure could prevent a significant amount of new pediatric asthma cases worldwide, particularly in urban areas, according to study findings published in The Lancet Planetary Health.
Researchers used data from the European Commission’s Joint Research Centre 2015 Global Human Settlement population grid. The population counts for the years 1975, 1990, 2000, and 2015 are at a spatial resolution of 250×250 meters, which is the finest resolution available with global coverage.
An estimated 4 million new pediatric asthma cases per year, or 13% of global incidence, may be attributable to ambient NO2 exposure. In addition, approximately 92% of NO2-attributable pediatric asthma occurred in areas in which NO2 concentrations are lower than the World Health Organization guideline of 21 ppb, with 97% of children living in said areas.
Regionally, Andean Latin America had the highest burden of new cases, followed by high-income North America, and high-income Asia Pacific. The latter had the largest percentage of regional pediatric asthma incidence attributable to NO2, followed by East Asia, high-income North America, southern Latin America, and Western Europe.
Nationally, China had the largest number of new asthma cases attributable to NO2 exposure at 760,000 cases per year. India, the United States, Indonesia, and Brazil followed with 350,000; 240,000; 160,000; and 140,000 cases, respectively. Of the 194 countries the researchers studied, Canada had the 34th highest incidence rate, which was the highest among high-income nations. Meanwhile, urban areas represented 64% of global cases. Lima, Peru; Shanghai, China; and Bogota, Colombia had the greatest burdens of new pediatric asthma cases with 690, 650, and 580 per 100,000 children annually, respectively. The percentage of new cases attributable to NO2 pollution ranged from 5.6% in Orlu, Nigeria to 48% in Shanghai, China among the 125 major cities examined.
This is the first study to provide global estimates of the annual burden of pediatric asthma incidence directly related to ambient NO2 exposure. However, it is not without limitations. Ground-based NO2 monitors are mostly in urban areas, which means the researchers’ global land-use regression model may have overestimated concentrations in rural areas. In addition, the NO2 concentrations used were the 2010 to 2012 annual average, but the population and asthma incidence rates were the 2015 estimates. The researchers also cautioned that variations in subnational incidence rates might exist because they relied on national pediatric asthma incidence rates.
Nevertheless, the researchers concluded, “Despite substantial decreases in NO2 concentrations over the past decade in large areas of the USA and western Europe, our findings suggest that existing levels of ambient NO2 pollution are a substantial risk factor for pediatric asthma incidence in both developed and developing countries, especially in urban areas.” To that point, the World Health Organization guideline for annual average NO2 concentrations might need to be reconsidered, they noted.
Achakulwisut P, Brauer M, Hystad P, Anenberg SC. Global, national, and urban burdens of paediatric asthma incidence attributable to ambient NO2 pollution: estimates from global datasets [published online April 10, 2019]. Lancet Planet Health. doi:10:1016/S2542-5196(19)30046-4