New research from the US suggests that having stressed parents may make it more likely that children will develop asthma that is triggered by air pollution, for instance from traffic and tobacco smoke. The researchers found that stress and low parental education were also linked with larger effects of exposure to tobacco smoke during pregnancy.

The study was led by Dr Rob McConnell, professor of preventive medicine at the Keck School of Medicine of the University of Southern California (USC) and deputy director of the Children’s Environmental Health Center at USC, and was published in the early online issue of the Proceedings of the National Academy of Sciences, PNAS on 17 July.

McConnell told the media that:

“We found that it was children exposed to the combination of air pollution and life in a stressful environment who were at highest risk of developing asthma.”

Asthma is the most common chronic illness among children in developed countries, and a number of studies have linked it to environmental factors, including stress and socioeconomic status.

For the study McConnell and colleagues used data on 2,497 children aged 5 to 9 who were taking part in the USC Children’s Health Study, a longitudinal study investigating respiratory health among children in 13 Southern California communities.

None of the children had a history of asthma or wheezing at the start of the study (2002-2003). The researchers followed them for three years and noted any parental reports of doctor-diagnosed new onset asthma in their children during that time.

The researchers also asked parents to fill in questionnaires so they could assess parental stress and socioeconomic status (they used education level for the latter) and whether the children had been exposed to tobacco smoke when in the mother’s uterus. The researchers also collected data on exposure to traffic-related air pollution using a line source dispersion model.

The results showed that:

  • Parental stress alone was not linked to a higher risk of developing asthma.
  • However, for children who lived in areas where exposure to traffic-related pollution was high, those with the most stressed parents had the highest risk of developing asthma.
  • Stress was also linked to a larger effect from being exposed to tobacco smoke while in the uterus.
  • There was a similar pattern of increased risk of asthma among children from low socioeconomic status families who also were exposed to either traffic-related pollution or in utero tobacco smoke.

The authors concluded that:

“These results suggest that children from stressful households are more susceptible to the effects of TRP [traffic-related pollution] and in utero tobacco smoke on the development of asthma.”

McConnell explained that:

“Air pollution can promote inflammatory responses in the airways of the lung, which is a central feature of asthma.”

“Stress may also have pro-inflammatory effects and this may help explain why the two exposures together were important,” he added.

The authors commented that children whose parents saw their lives as unpredictable, uncontrollable or overwhelming were more likely to get asthma triggered by traffic-related polllution. They suggested that stress associated with poverty may explain why asthma prevalence is often higher in communities of lower socioeconomic status.

McConnell said:

“Childhood asthma is a complex disease that probably has many contributing causes.”

“Further study of effects of exposure to air pollution in combination with stressful environments associated with poverty and other social factors could contribute to our understanding of why the disease develops,” he suggested.

The National Institute of Environmental Health Sciences, the US Environmental Protection Agency, the National Cancer Institute, the Hastings Foundation and the Canadian Institutes of Health Research funded the study.

,i>”Parental stress increases the effect of traffic-related air pollution on childhood asthma incidence.”
Ketan Shankardass, Rob McConnell, Michael Jerrett, Joel Milam, Jean Richardson, and Kiros Berhane.
PNAS, published online before print 17 July 2009.

Additional source: USC News.

Written by: Catharine Paddock, PhD