NO2 exposure in infancy is strongly linked with later development of childhood asthma

A research team led by UCSF scientists has found that exposure in infancy to nitrogen dioxide (NO2), a component of motor vehicle air pollution, is strongly linked with later development of childhood asthma among African Americans and Latinos.

The researchers said their findings indicate that air pollution might, in fact, be a cause of the disease, and they called for a tightening of U.S government standards for annual exposure to NO2.

The study is reported online currently in the American Journal of Respiratory and Critical Care Medicine ahead of print publication.

In the study, the largest to date of air pollution exposure and asthma risk in minority children in the United States, the team found that for every five parts per billion increase in NO2 exposure during the first year of life, there was a 17 percent increase in the risk of developing asthma later in life.

The study involved 3,343 Latino and 977 African American participants.

"Many previous studies have shown an obvious link between traffic-related pollution and childhood asthma, but this has never been thoroughly looked at before in an all-minority population," said lead author Katherine K. Nishimura, MPH, a graduate student in the laboratory of senior author Esteban G. Burchard, MD, MPH, a UCSF professor of bioengineering and therapeutic sciences and medicine and director of the UCSF Center for Genes, Environment & Health.

Minorities tend to live in areas of higher air pollution and have a higher risk of developing asthma, the researchers said.

What made the current study different from previous research, said Nishimura, was that the scientists looked retrospectively at the study participants' exposure to air pollution in early childhood, before they developed asthma. Children who developed asthma before this exposure period were excluded.

"Any participant with asthma in this study was exposed to air pollution in infancy, before they developed the disease, which is a step in the right direction in inferring causality," said Nishimura.

"This work adds to the growing body of evidence that traffic-related pollutants may be causally related to childhood asthma," said Burchard.