Kids who dangle from the monkey bars in parks where the air is heavy with pollution are more likely to develop asthma than those who breathe in cleaner air. And if their parents are stressed, the chances are even higher that they'll have to carry a puffer in their backpacks.
New research from the University of Southern California suggests children of stressed-out parents in high-pollution areas are more likely to have asthma than children in high-pollution areas with more relaxed mothers and fathers.
The study, which will be published in the July 28 issue of the Proceedings of the National Academy of Sciences journal, followed 2,497 five-to-nine-year-olds from Southern California and tracked where they lived, their socioeconomic status, and their parents' stress level. Over the course of the three years, 120 children developed asthma.
At the start of the study, parents were asked a series of questions about whether they perceived their lives as "unpredictable, uncontrollable and overwhelming." Researchers found that the kids who had higher-stressed parents had a 50 per cent increased rate of developing asthma from living in zones with high levels of traffic-related pollution. When stress was taken out of the equation, there was only a 30 per cent increase in cases of asthma for children who lived in high-pollution areas versus those in low-pollution communities.
"What we've found is the dual exposure of stress and pollution could contribute to the development of asthma," said Ketan Shankardass, one of the study's authors.
Mr. Shankardass, who works at St. Michael's Hospital's Centre for Research on Inner-City Health in Toronto, said stress causes airway inflammation and the body typically responds by calming that inflammation. But when people are chronically stressed, that controlling mechanism gets worn out and fails. With asthmatics, this can cause asthma attacks.
Mark Greenwald, a Toronto physician who specializes in treating asthma and allergy sufferers, said the results of the study don't surprise him. When parents are overwhelmed by life events, that stress is often passed on to their children.
The mother of one of his 14-year-old patients complained about high levels of stress, which he said might be affecting the severity of her son's asthma.
But he said where stress and asthma overlap can create a chicken-or-egg scenario: Do kids with stress develop asthma, or does having asthma cause stress?
Mr. Shankardass underscored that the study didn't show that stress alone was associated to an increased risk of asthma, but rather it was a combination of stress and environmental conditions.
"Asthma is a really complex disease," he said. "We might have discovered something that plays a role in that development process."
In cases where parents said they battled stress but did not live in a high-pollution area, there was no increase in asthma cases, said Mr. Shankardass.
In 2007, the Public Health Agency of Canada reported 485,700 children from ages four to 11 had asthma. The disorder affects about 16 per cent of children in that age range.