Health experts have been saying for years now that environmental pollution is one of the leading causes of the increase in childhood cases of asthma. But a new study has found that when you add parental stress to pollution, you get kids who are at an even greater risk.
In the study, published in the Proceedings of the National Academy of Sciences, 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 Center at University of Southern California in Los Angeles, told Reuters Health.
The study 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. For three years, 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. 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. But the study did find that a child exposed to traffic-related pollution whose parents indicated high levels of stress had a 51 percent higher risk of developing asthma during follow-up compared with a child exposed to traffic pollution but whose parents had low levels of stress.
Why would parental stress lead 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.