"This is the best evidence yet of a chronic effect of air pollution in children," says John Peters, M.D., D.Sc., USC professor of preventive medicine and one of the study 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."
The report, released in the October issue of the American Journal of Respiratory and Critical Care Medicine, covers smog's health effects on children over the first four years of the study.
Normally, children's lung function grows steadily as they grow up. 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 awhile before slowly declining as a person ages.
Researchers with the Children's Health Study 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. Each year, USC scientists tested lung function by having each child take a deep breath, then measuring how much air the kids could blow out and how fast. The 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 fourth graders, followed from age 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 compared to 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," says W. James Gauderman, Ph.D., USC 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 notes, 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 tests air in the 12 communities, from Atascadero in the north to Alpine in the south. Locations in the Inland Empire were chosen because 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.
The USC team released preliminary results of the Children's Health Study in 1999, which provided an initial hint that lung function is lower in children who breathe the most polluted air.
The researchers will continue monitoring students into their teens and possibly into adulthood. They also are following students who have moved away to lower pollution areas, to see if their lung function rebounds.
In general, air quality in Southern California has improved over the last two decades. Says Gauderman, "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."
For more information about the Children's Health Study, please visit the researchers' website at: www.usc.edu/medicine/scehsc.