Stress, air pollution and asthma risk

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.

Researchers studied 2,497 American children aged 5-9 years old to investigate whether low socioeconomic status or parental stress modified the effect of traffic related pollution and tobacco smoke exposure on the onset of asthma in children. The children 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.

It was 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 exposed only to pollution.

Stress, as well as low levels of education in the parents, was also associated with larger effects of exposure to tobacco smoke during pregnancy.

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.

The researchers concluded 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. Air pollution can promote inflammation 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.