THURSDAY, Jan. 31, 2002 (HealthDayNews) -- Exercising when there are high concentrations of ozone in the air is associated with an increased risk that a child will develop asthma, a California study finds.
Children who played at least three outdoor sports in high-ozone areas were three times more likely to develop asthma than children who did not play any sports, a group led by Dr. Rob McConnell of the University of Southern California reports in the Feb. 2 issue of The Lancet. There was no such risk for children in low-ozone areas.
"There is a lot of evidence that air pollution makes asthma worse in children who have asthma," says McConnell, an associate professor of preventive medicine at USC's Keck School of Medicine. "There has been relatively little evidence that air pollution actually causes asthma. Our study provides evidence that ozone pollution can increase the risk of asthma in children who exercise heavily."
Ozone is a highly reactive oxygen molecule that is created naturally in the atmosphere when ordinary oxygen reacts to lightning. As a pollutant, it comes mostly from automobile exhausts, although some is emitted by power plants and factories. Asthma is the most common chronic disease of childhood, and its incidence has been increasing in the United States and other developed countries.
A variety of mechanisms, including air pollution, have been proposed as causes of the increase in asthma, which has been especially marked in athletes. But there have been no studies that have looked at young athletes to see what might increase the risk, the USC researchers say.
For five years, McConnell and his colleagues followed more than 3,500 children from schools in 12 southern California communities, six with high ozone levels, the other six with low ozone levels. The researchers looked at the amount of time the children spent outdoors and whether they played outdoor sports.
Overall, the risk of asthma was 40 percent higher in children who spent a lot of time outdoors in the high-ozone communities, compared to those in low-ozone communities, the researchers report, with the threefold increased risk noted in children who competed in a number of sports. Competing in outdoor sports in the low-ozone communities did not increase the risk of asthma. No association was found in exposure to other air pollutants, such as nitrogen oxide.
"Our study is one piece of a complicated asthma puzzle," McConnell says. "On a scientific level, we don't really understand what it is that causes this disease. More research needs to be done to understand the relationship between ozone and other pollutants and asthma."
But the report notes that "the increased pulmonary dose of ambient ozone resulting from heavy exercise, combined with exposure to outdoor and indoor allergens, is one possible mechanism for inducing new onset asthma."
"This is one more piece of evidence of the deleterious effects of ozone," says Dr. Norman H. Edelman, a consultant for scientific affairs to the American Lung Association. "It is obvious that ozone in levels that exist widely are associated with asthma."
But cause and effect are not clear, Edelman says. "It could mean that mild cases of asthma are not detected, and ozone exposure makes them evident," he says. "One thing to be aware of is that some studies have shown that as many as one-third of children with asthma are undiagnosed."
McConnell says that "our research suggests that our government must do more to control air pollution. It decreases lung function in older people and increases school absences. There is a tremendous social cost of air pollution in general."
And parents should not tell their children to avoid exercise and sports, McConnell says. "Exercise is good for children, for a variety of reasons. You do not help children if you prevent them from exercising," he says.
What To Do
"When your local health or environmental agency predicts a high- pollution day, we advise children not to do heavy outdoor exercise," McConnell says. "Here in southern California, when the air pollution authorities expect heavy air pollution, we issue a school advisory."
You can learn more about what the dangers of ozone to kids's lungs from the American Lung Association. You can also try the American Academy of Allergy, Asthma, and Immunology for information on asthma.
