NIEHS-funded researchers find low-level ozone increases respiratory risk of asthmatic children

New evidence gathered in a study funded by the National Institute of Environmental Health Sciences suggests that asthmatic children who use maintenance medication are particularly vulnerable to the effects of ground-level ozone, even at levels well below the federal standard set by the Environmental Protection Agency.

Their research results were published Oct. 8 in the Journal of the American Medical Association. The study was conducted at the Yale University School of Medicine. NIEHS is one of the federal National Institute of Health.

“Although the 1-hour average ozone levels in our study were well below the federal standard, statistical analysis revealed that for every 50 parts per billion increase in ozone, the likelihood of asthma symptoms the following day increased by more than 35 percent among asthmatic children on maintenance medication,” said Brian Leaderer, Ph.D., the Susan Dwight Bliss Professor of Epidemiology at Yale University and principal investigator for the study.

Asthma, an inflammatory disorder of the airways that is characterized by periodic attacks of wheezing, shortness of breath and coughing, can be triggered by inhaled allergens such as pet dander, dust mites, molds or pollens. But researchers have also shown that air pollutants such as ground-level ozone, an active form of oxygen that is the prime ingredient of urban smog, and fine particulate matter, which includes dust, dirt, smoke and soot from a variety of natural and man-made sources, can significantly aggravate asthma symptoms.

Repeated exposures to ozone and fine particles at or above the federal standards can irritate or damage sensitive tissue in the airways and lungs, making breathing even more difficult for asthmatics and causing more attacks, increased use of medication, and more visits to hospital emergency clinics. Children are particularly vulnerable to these exposures because their respiratory systems are still developing, and they tend to spend more time in outdoor activities than do adults.

Earlier studies of children with asthma living in highly polluted regions, such as Mexico City and Los Angeles, all concluded that exposure to ozone and fine particles in excess of 120 parts per billion (ppb) and 65 micrograms per cubic meter ( g/m3), respectively, greatly increased the risk for respiratory symptoms. “We wanted to design a study that examined the effects of air pollution on a particularly vulnerable population – children with active asthma – in regions where pollution levels were somewhat lower than those in major metropolitan areas,” said Leaderer.

Study participants included 271 asthmatic children living in Connecticut and the Springfield area of Massachusetts during the spring and summer of 2001. The investigators conducted monthly interviews with the mothers to obtain information on each child’s daily wheezing, coughing, shortness of breath, chest tightness, and asthma medication use. Daily measurements of ground-level ozone and fine particulate matter were provided by the Departments of Environmental Protection of Connecticut and Massachusetts.

Although mean 1-hr average ozone concentrations measured only 59 ppb, variations in daily levels had a profound effect on the respiratory symptoms of those who used maintenance medication. A 50 ppb increase in 1-hr ozone was associated with a 35 percent increase in wheezing, and a 47 percent increase in chest tightness. The highest ozone levels were associated with increased shortness of breath and rescue medication use.

However, the investigators did not find a significant relationship between the children’s exposure to fine particulate matter and daily respiratory symptoms or rescue medication use. Furthermore, no exposure-dependent outcomes were observed for either pollutant category among children who did not use maintenance medication.

“Our results suggest that ground-level ozone is strongly associated with adverse health effects in children with asthma, even at levels below the current federal standards,” said Leaderer.

Other co-investigators from Yale University include Janneane Gent, Ph.D., Elizabeth Triche, Ph.D., Theodore Holford, Ph.D., Kathleen Belanger, Ph.D., and Michael Bracken, Ph.D., along with William Beckett, M.D., at the University of Rochester.