McConnell R, Berhane K, Gilliland F, et al. Lancet. 2002;359:386–391
Purpose of the Study.
The aim of this study was to investigate the relationship between newly diagnosed asthma and team sport participation in children exposed to different concentrations and types of air pollutants.
A group of 3535 children, 9 to 16 years old, with no previous history of doctor-diagnosed asthma on a baseline questionnaire, were recruited from 12 southern California schools.
Interviewers administered baseline and yearly questionnaires regarding new diagnoses of asthma, asthma symptoms, and participation in any of 8 possible team sports in the past year. Air pollution monitoring stations in each community measured ozone, nitrogen dioxide, and particles <10 μm in diameter 10 (PM) every hour and PM 2.5 and acid vapor every 2 weeks. The risk of asthma was assessed relative to the number of high- or low-intensity team sports played at study entry, in communities with high or low levels of the measured air pollutants.
The overall risk of developing asthma was not greater in the high-pollution communities compared with the low-pollution communities, after adjusting for baseline risk factors. In the 6 high-ozone communities, there was a 3.3-fold increased relative risk of developing asthma in children playing 3 or more team sports (95% confidence interval [CI]: 1.9–5.8) compared with those playing no sports. No increase in this relative risk was observed in children playing team sports in low-ozone communities. Across all communities, there was a 1.8-fold increased risk (95% CI: 1.2–2.8) of asthma in children who had played 3 or more team sports in the past year. Spending a large amount of time outside in high-ozone communities was independently associated with an increased risk of asthma. Exposure to pollutants other than ozone was not associated with a higher incidence of asthma.
The incidence of new asthma diagnoses was associated with heavy exercise in communities with high ozone levels, suggesting a contribution of outdoor exercise and air pollution to the development of childhood asthma.
The results of this study suggest that increased ventilation rates of air containing high levels of ozone during heavy exercise may predispose children to developing asthma. Although playing high-intensity sports in high-ozone communities was associated with a greater incidence of asthma, data comparing the incidence of asthma in children playing high- and low-intensity sports was not shown. In addition, high-intensity individual sports, such as running or cycling, were not included in the questionnaires, so some children may have exercised more intensely than was documented. Ozone levels may be several-fold higher outdoors, so a comparison of the effects of outdoor and indoor exercise would have been useful. A description of asthma symptoms and the relationship of symptoms to sports participation would have been helpful to distinguish chronic wheezing from exercise-induced bronchospasm. Additional studies focusing on personal exposure to ozone, the intensity and location of exercise, and asthma symptoms will be helpful to further investigate this challenging question.