Dirty Air Stunts Lung Growth.

Long-term exposure to air pollutants such as nitrogen dioxide and particulate matter can cause reduced lung growth in children, and the effects are more pronounced in areas where air pollution is highest, according to findings from the Children's Health Study, a 10-year longitudinal study at the University of Southern California in Los Angeles.

Started in 1993, the Children's Health Study is following the respiratory development of over 3,000 fourth-, seventh-, and tenth-graders from 12 communities throughout California with different levels and types of air pollution. Each year the students undergo lung function tests at school. The researchers also measure levels of ozone, nitrogen dioxide, particulate matter smaller than 10 microns in diameter, and acid vapors at each test site (gasoline and diesel engine emissions are the major source for all four pollutants). Data collected during the first four years of the study were reported in the October 2000 issue of the American Journal of Respiratory and Critical Care Medicine by lead author W. James Gauderman, an assistant professor of preventive medicine at the university, and his colleagues.

Exposure to nitrogen dioxide, particulate matter, and acid vapors has been found to have the greatest association with impaired lung growth, with ozone having a statistically insignificant effect. Compared to students living in the least polluted communities, children living in the most polluted communities have shown a reduction in two measures of lung function: a cumulative 3.4% reduction in [FEV.sub.1] (forced expiratory volume) and a 5.0% reduction in MMEF (maximal mid-expiratory flow). The [FEV.sub.1], or amount of air expelled in the first second of blowing, measures how well the large and medium-sized airways in the lung are functioning, explains Gauderman, whereas the MMEF measures small airway function. Although children with reduced lung growth probably experience no outward symptoms of lung problems, they may be at increased risk as adults for chronic respiratory problems such as asthma and emphysema, says Gauderman. The longitudinal effect found in the first cohort has now been replicated in a second cohort, with identical results.

Children who spend the most time outdoors experience the greatest effect of air pollution on their lung function. Generally, advises Gauderman, children should minimize outdoor playing on high-pollution days. Reports on regional air pollutant levels are often available through TV weather channels and local meteorology offices.

"No one else has followed a cohort of schoolchildren of this age for this long a time," says pulmonologist David Bates of the University of British Columbia in Vancouver. He says the study's findings are "a major contribution" in understanding the long-term consequences of air pollution on children's lungs. Moreover, in 120 of the children who moved out of the study area and were tracked separately, lung function growth was greater in those who moved to cleaner environments compared to those who moved to more polluted areas. This is a "striking confirmation of the longitudinal study," Bates adds.