LOS ANGELES, CALIFORNIA. The incidence of asthma among children in developed countries is increasing rapidly. The causes of this epidemic are not entirely clear, but the exposure to allergens and the increased emphasis on protection from early-life infections ("hygiene hypothesis") are thought to play a role. Researchers at the University of Southern California School of Medicine now report that frequent participation in team sports in areas of heavy ozone pollution is closely linked with an increased evidence of childhood asthma.
Their study involved 3535 asthma-free children from 12 southern California communities. Monitoring
stations were set up in each community and the air concentration of ozone, nitrogen dioxide, and particulate
matter were measured daily during the five-year study period. After five years, 265 of the children had
developed asthma. The researchers found that children who lived in communities heavily polluted with
ozone were 3.3 times more likely to develop asthma if they regularly participated in three or more team
sports than if they played no sports or lived in communities with low ozone levels. They conclude that the
development of asthma is linked to heavy exercise combined with exposure to high levels of ozone.
Nitrogen dioxide levels and the level of particulate matter were not related to asthma incidence.