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 ommon air pollutants slow children's lung development over time, accord ing to results from the University of Southern California-led Children's Health Study. The 10-year-long study is considered one of the nation's most comprehensive studies to date of the long-term effects of smog on children. The study was initiated with support from the California Air Resources Board and was funded by the National Institute of Environmental Health Sciences, the Environmental Protection Agency and the Hastings Foundation.
 "This
is the best evidence yet of a chronic effect of air pollution
in children," says John Peters, MD, DSc, 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, PhD, 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." 
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