Asthma
cases dropped when air pollution declined

Decreases in
air pollution levels are known to reduce the number of asthma attacks
experienced by children who have the disease. But whether pollution influences
how many children are newly diagnosed with asthma has been less clear.

Researchers
from the University of Southern California led by Dr. Erika Garcia used data
from the Southern California Children’s Health Study to better understand this
relationship. The study has collected health information from children in 16
diverse communities in Southern California for over 25 years.

What is
the association between reductions in regional air pollutant concentration and
incidence of childhood asthma?

The
researchers followed large groups of children living in nine of these
communities over three time periods from fourth grade through the end of high
school: from 1993-2001, from 1996 to 2004, and from 2006 to 2014.

Air
pollution declined steadily in the U.S. during the study period. Air pollutant
monitoring stations tracked these changes over time in each of the
participating communities. The stations have continuously measured air
pollution since the start of the study.

Design,
Setting, and Participants

The
researchers used air pollutant measurements from the first year of each time
period as a benchmark for the overall air quality each group experienced. They
then compared new diagnoses of asthma between the three groups. The study was
funded in part by NIH’s National Institute of Environmental Health Sciences
(NIEHS) and National Heart, Lung, and Blood Institute (NHLBI). Results were
published on May 21, 2019, in JAMA.

Air
pollution declined overall in the communities during the study. Those
communities that started out with more pollution experienced larger decreases.

Out of more
than 4,000 children included in the study, about 500 developed asthma.
Reductions in two of the pollutants measured—nitrogen dioxide and a type of
fine particle called PM2.5—were associated with reductions in new asthma
diagnoses over the course of the study.

These
reductions in nitrogen dioxide and PM2.5 over two decades were associated with
an approximately 20% reduced risk of asthma development. This was true
regardless of children’s sex, ethnicity, race, exposure to tobacco smoke in the
home, and other factors that can influence the development of asthma.

“This is
encouraging news as it shows the number of new cases of asthma in children can
be reduced through improvements in air quality,” says Dr. Kiros Berhane, one of
the study’s authors.

This study doesn’t prove that these specific compounds are responsible for cases of asthma. They may be markers for the general mixture of traffic-related air pollution. But the findings add to growing evidence showing the health benefits of cleaner air.

{Source – National Institutes of Health (U.S. Department of Health and Human Services)}