A US study in this weeks issue of THE LANCET highlights how children playing outdoor team sports in areas of high ozone concentration could be three times more likely to develop asthma than children who do not take part in sporting activities.

Asthma is the most common chronic disease of childhood; its prevalence and incidence have been increasing in children in developed countries during the past few decades, although the causes of this epidemic remain unclear. Little is known about the effect of exposure to air pollution during exercise or time spent outdoors on the development of asthma. Rob McConnell and colleagues from Keck School of Medicine of the University of Southern California, Los Angeles, USA, investigated the relation between newly-diagnosed asthma and team sports in a population of children exposed to different concentrations and mixtures of air pollutants.

Around 3500 children (who had no history of asthma) were recruited from schools in 12 communities in southern California and were followed-up for up to 5 years. 265 children reported a new diagnosis of asthma during follow-up. Children who played three or more outdoor sports in high-ozone environments were more than three times as likely to develop asthma compared with children who did not play any sports. There was no increased risk where ozone concentrations were low. Children who spent time outside in areas with high ozone concentrations were 1.4 times more likely to develop asthma than children in areas of low ozone concentration. Other environmental pollutants- nitrogen dioxide, particulate matter, and inorganic-acid vapour-were not associated with an increased asthma risk.

Rob McConnell comments: We conclude that the incidence of new asthma diagnoses is associated with heavy exercise in communities wi
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Contact: Richard Lane
richard.lane@lancet.com
44-20-7611-4076
Lancet
31-Jan-2002