Air pollutants from traffic are associated with increased asthma severity levels in pregnant asthmatic women, according to a new study.
"Air pollution is a known trigger for asthma symptoms," said lead author Janneane Gent, PhD, Research Scientist in Epidemiology (Environmental Health) at the Yale School of Public Health. "In our study, exposures were assessed using a sophisticated air pollution modeling system (Community Multiscale Air Quality, CMAQ) that permits community-level estimates (i.e., close to where the subject resides) instead of assigning regional measurements made at Environmental Protection Agency (EPA) central site monitors to all subjects. Using community-level estimates, we found that exposure to nitrogen dioxide at levels much lower than the current EPA standard was associated with increased risk of asthma morbidity."
The results of the study will be presented at the ATS 2013 International Conference.
The study enrolled 637 pregnant women (<24 weeks gestation) with active asthma (physician-diagnosed asthma plus symptoms and/or asthma medication use in the previous 12 months) from Connecticut and Western Massachusetts. Asthma severity levels, measured by days of wheeze, medication use, and a 5-level asthma severity score were assessed through phone interviews for each 28-day gestational month.
Exposure to nitrogen dioxide, fine particulate matter, and the elemental carbon content of fine particulate matter were estimated using the CMAQ modeling system. Analyses of the relationship between exposure to traffic-related pollutants and asthma severity were adjusted for a number of possible confounding factors, including month of pregnancy, pre-pregnancy body mass index, demographics, health, household exposures and season.
Mean community-level predicted concentrations for nitrogen dioxide, elemental carbon and fine particulate matter were 23.7 parts per billion (ppb), 0.67 micrograms (one-millionth of a gram) per cubic meter of air (g/m3) and 11.1 g/m3, respectively.
Each 10 ppb increase in community-level nitrogen dioxide was associated with an increased risk of wheeze, with an odds ratio (the odds that an outcome will occur after a particular exposure, compared to the odds of the outcome occurring in the absence of that exposure) of 1.27. Each 10 ppb increase in nitrogen dioxide was also associated with a higher asthma severity score (odds ratio 1.31). Similarly, each 0.5 g/m3 increase in elemental carbon was associated with an increased risk of wheeze (odds ratio 1.30) and higher asthma severity score (odds ratio 1.32).
Exposure to fine particulate matter did not significantly increase asthma morbidity or asthma severity score.
"Exposure to air pollution from traffic is known to have a number of deleterious effects on human health," said Dr. Gent. "Our study suggests that exposures to community-level concentrations of traffic-related pollutants are associated with increased asthma morbidity, and that these pollutant concentrations are likely to be lower than those measured at EPA central monitoring sites."