Smog Stunts Lung Growth in Children, Study Finds

by Alicia Di Rado
W. James Gauderman, assistant professor of preventive medicine, lead author of a USC-led study on the effects of smog on children, speaks at an Oct. 19 press conference. A map shows the 12 communities that were studied.

Photo by Jon Nalick
Common air pollutants slow children’s lung development over time, according to results from the USC-led Children’s Health Study.

The study is considered one of the nation’s most comprehensive studies to date of the long-term effects of smog on children.

“This is the best evidence yet of a chronic effect of air pollution in children,” said John Peters, professor of preventive medicine and one of the study’s authors. “Long-term exposure to air pollution has long-term effects on children’s lungs, and the effects are more pronounced in areas of higher air pollution.”

Preventive medicine researchers have monitored levels of major pollutants in a dozen Southern California communities since 1993, while carefully following the respiratory health of more than 3,000 students. The report, released in the October issue of the American Journal of Respiratory and Critical Care Medicine, covered smog’s health effects on children over the first four years of the study.

Each year of the study, USC scientists tested lung function by having each child take a deep breath, then measuring how much and how fast kids could exhale. Researchers showed that as children grow up, those who breathe smoggier air tend to lag in lung function growth behind children who breathe cleaner air. Children with decreased lung function may be more susceptible to respiratory disease and may be more likely to have chronic respiratory problems as adults.

The air pollution effects were most evident in the children followed from ages 10 to 14. On average, over the four years, the lung function growth rate of children in the most polluted community was about 10 percent lower than that of children in the least polluted community. Similar effects on lung function were observed in boys and girls, and in asthmatic and healthy children.

“The association we see with air pollution also is stronger in children who spend more time outdoors,” said W. James Gauderman, assistant professor of preventive medicine and the study’s lead author. “That is consistent with what we would expect from a detrimental effect of outdoor air pollution.”

One surprising finding of the study, Gauderman noted, is that ozone did not appear to play a major role in the pollution’s effects on children’s lungs. Instead, the offenders were nitrogen dioxide, microscopic particles known as particulate matter and acid vapors. All come directly or indirectly from the burning of fossil fuels (the exhaust from a car or truck, for example) as well as from emissions from industrial plants and other sources.

Millions of Southern Californians breathe polluted air every day, especially on days when levels of pollutants exceed state and federal standards for air quality. The area’s layout as a basin, as well as the typical sunny weather and omnipresent vehicle traffic, combine to keep high levels of pollutants in the air. Although polluted air has long been known to cause immediate uncomfortable symptoms such as eye irritation, coughing and chest tightness, long-term or chronic effects have been less clear. In the current research, though, scientists have begun to demonstrate effects over time.

The researchers recruited 150 fourth graders, 75 seventh graders and 75 tenth graders in 1993 from each of the 12 communities. For this study, the California Air Resources Board routinely tested air in the 12 communities, from Atascadero in the north to Alpine in the south. Locations in the Inland Empire were chosen be cause they were known to have relatively high levels of pollutants, while northern communities were chosen because they have lower pollution levels.

Researchers found that, on average, lung function growth tended to be higher in cleaner communities and lower in areas with more air pollution.

Normally, children’s lung function grows steadily as they mature. Females reach their greatest potential lung function when they are in their late teens, while males reach their maximum lung function when they are in their early 20s. After that, lung function stays level for a while before slowly declining as a person ages.

The researchers will continue monitoring students into their teens and possibly into adulthood. They are also following students who have moved away to less polluted areas, to see if their lung function rebounds.

In general, air quality in Southern California has improved over the last two decades, Gauderman said. “Our results indicate that continued reduction of air pollution, through the efforts of both regulators and the public, will lead to improved health in our children.”

The study was undertaken with support from the California Air Resources Board. The National Institute of Environmental Health Sciences, the Environmental Protection Agency and the Hastings Foundation provided additional funding.