July 21, 2009 -- Children living in high-stress homes may be more at risk for asthma associated with environmental triggers like traffic-related air pollution and exposure to cigarette smoke, new research shows.
Among children who had regular exposure to pollution from traffic exhaust, those living in households with the most stress were 50% more likely to develop asthma than those living in low-stress homes.
Stress did not have a big influence on asthma risk when the environmental trigger was not present, says study researcher Rob S. McConnell, MD, of the University of Southern California (USC) Keck School of Medicine.
“It is well known that pollution can cause inflammatory effects in the lungs, and inflammation is a cardinal feature of asthma,” he tells WebMD. “Stress can also have a pro-inflammatory effect, so it is certainly plausible that the impact of stress and air pollution together might be worse than either one by itself.”
Pollution, Stress, and Asthma
The study included about 2,500 children between the ages of 5 and 9 enrolled in a larger study examining the effect of air pollution on respiratory health.
None of the children had evidence of asthma or wheeze at enrollment, and all were followed for three years.
As a marker of childhood stress, which is not easy to measure directly, parents completed questionnaires examining their own stress levels. Researchers also collected other information, including smoking exposure, household characteristics, and parental education, which is an indicator of socioeconomic status.
During the three-year study, 120 children developed asthma
Although stress alone did not appear to increase asthma risk, McConnell and colleagues from USC and Toronto’s St. Michael’s Hospital found that the combination of living in a stressful home and living near high levels of traffic-related pollution was a bigger risk factor for asthma than living in a traffic-congested area alone.
Children whose mothers smoked during pregnancy were also more likely to develop asthma when their home environment was stressful.
“This research provides some new clues about what might be contributing to this complex disease that almost certainly has multiple causes,” McConnell says.
Asthma Incidence Growing
According to the CDC, the prevalence of asthma increased by 75% between 1980 and 1994, and asthma rates among children under age 5 increased by more than 160% during these years.
About 300 million people worldwide are estimated to have asthma, and the World Health Organization projects that this number will grow to 400 million by the year 2025.
Asthma researcher David B. Penden, MD, of the University of North Carolina tells WebMD that it is increasingly clear that exposure to environmental pollutants like traffic exhaust and cigarette smoke can trigger asthma symptoms in people with the disease.
There is also growing evidence that these exposures play a role in the development of asthma.
The research by McConnell and colleagues is among several recent studies to suggest a role for stress in the development of asthma.
“We are beginning to learn a lot about the role of stress on a host of different diseases related to immune function,” he says.
He cites a series of studies from researchers at Harvard’s Beth Israel Deaconess Medical Center finding stress to be associated with an increase in wheezing and other asthma risk factors in infancy.
“I think the data are increasingly convincing even though a lot is still not understood about the impact of stress on disease,” he says.