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Children with stressed-out parents may be more prone to developing asthma associated with environmental "triggers" such as high levels of traffic-related pollution and tobacco smoke, hints a new study.
In the study, researchers found that children whose parents reported high levels of psychological stress, and who were exposed to cigarette smoke in the womb and to traffic-related pollution early in life, had a much higher risk of developing asthma, compared to children only exposed to pollution.
"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," Dr Rob McConnell, deputy director of the Children's Environmental Health Centre at University of Southern California, US, told Reuters Health.
For three years, McConnell and colleagues followed 2,497 children aged 5 to 9 years who were living in Southern California and who were free of asthma or wheezing at the outset. The researchers measured stress in the parents using a standard questionnaire, and collected data on air pollution and exposure to tobacco smoke during pregnancy.
During the study, 120 of the children developed asthma.
Stress alone doesn’t increase risk
According to a report in an early online edition of the Proceedings of the National Academy of Sciences, parental stress alone did not increase the risk that a child would develop asthma.
However, a child exposed to traffic-related pollution whose parents felt their lives were "unpredictable, uncontrollable, and overwhelming" - suggestive of high levels of stress - had a 51% higher risk of developing asthma during follow up compared with a child exposed to traffic pollution but whose parents had low levels of stress.
Stress, as well as low levels of education in the parents, was also associated with larger effects of exposure to tobacco smoke during pregnancy.
Psychological stress promotes asthma
These findings, the researchers say, show that psychological stress in parents can make children more susceptible to asthma.
Air pollution can promote inflammation in the airways of the lung, "which is a central feature of asthma," McConnell said. "Stress may also have pro-inflammatory effects, and this may help explain why the two exposures together were important," he added.
"Childhood asthma is a complex disease that probably has many contributing causes," McConnell noted. "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." – (Megan Rauscher/Reuters Health, July 2009)
SOURCE: Proceedings of the National Academy of Sciences Early Edition, online July 20. 2009.
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