Cleaner Air Improves Lung Development in Children

Yael Waknine

March 05, 2015

Long-term improvements in air quality are linked to clinically significant improvements in pediatric lung development and function, according to a longitudinal cohort study published in the March 5 issue of the New England Journal of Medicine.

"[T]he results of our investigation make it clear that broad-based efforts to improve general air quality are associated with substantial and measurable public health benefits," write W. James Gauderman, PhD, from the Department of Preventive Medicine at the University of Southern California in Los Angeles, and colleagues.

Prior studies suggest that outdoor air pollution restricts pulmonary growth in children, increasing not only their risk for asthma but also their susceptibility to respiratory and cardiovascular disease in adulthood. However, the respiratory health benefits of reducing pollution have not been fully established.

To this end, investigators from the Southern California Children's Health study measured changes in pediatric pulmonary function during a period characterized by implementation of aggressive pollution-control strategies. In particular, adoption of a more stringent vehicle emissions policy yielded dramatic reductions in exposure to nitrogen dioxide and particulate matter with aerodynamic diameters of less than 2.5 μm (PM25) and 10 μm (PM10), respectively.

The researchers enrolled a total of 2120 children from five distinct communities in three cohorts: 1994 to 1998, 1997 to 2001, and 2007 to 2011. Mean age at the beginning and end of each cohort was 11 years and 15 years, respectively, capturing a 4-year period of rapid lung development in both boys and girls. Annual measures of pulmonary function included maximal forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC).

Longitudinal results from each of the five communities were consistent, in that 4-year FEV1 and FVC significantly improved with declining levels of nitrogen dioxide (P < .001 for both), PM25 (P = .008 and P < .001), and PM10 (P < .001 for both). The improvements were significant in both sexes and among children with and without asthma. Adjustment for potential confounders, such as smoking or exposure to indoor allergens, did not affect the significance or magnitude of the association.

Overall, mean 4-year FEV1 and FVC growth increased by 91.4 and 168.9 mL per decrease of 14.1 ppb in nitrogen dioxide level (P < .001), by 65.5 and 113.0 mL per decrease of 8.7 μg/m3 in PM10 level (P < .001), and by 65.5 and 126.9 mL per decrease of 12.6 μg/m3 in PM25 level (P = .008 and P < .001), respectively.

"These results suggest that the children born after air-pollution levels had declined in these communities had greater lung-function growth," Douglas W. Dockery, ScD, and James H. Ware, PhD, from the Harvard T.H. Chan School of Public Health in Boston, Massachusetts, comment in an accompanying editorial.

Indeed, further analysis revealed that the prevalence of low FEV1, defined as 80% of predicted value, was only 3.6% at the end of the last cohort, compared with 7.9% and 6.3% in the earlier cohorts (P < .005).

"Some have argued that the substantial improvements in air quality over the past 40 years are sufficient to protect public health and that there is little evidence to support more stringent standards. However, the current report and other studies suggest that further improvement in air quality may have beneficial public health effects," the editorialists conclude.

Supported in part by contracts with the Health Effects Institute and the California Air Resources Board and by grants from the National Institute of Environmental Health Sciences. Dr McConnell reports holding a research contract from funds from an air quality violations settlement between the South Coast Air Quality Management District, a California state regulatory agency, and BP. The other authors and the editorialists have disclosed no relevant financial relationships.

N Engl J Med. 2015;372:905-913, 970-972. Article full text, Editorial full text


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