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February 4, 2014

SickKids-led study shows how even modest levels of traffic pollution triggers asthma in some Toronto kids

As the fourth-largest city in North America, Toronto is a busy metropolis that matches its peers in many areas; it even surpasses some when it comes to good air quality due to relatively modest levels of traffic-related air pollution. Despite this limited exposure, young Torontonians are not immune to the detrimental lung health effects of traffic-related air pollution, according to a recent study published in the advance online edition of Environment International. The research was led by The Hospital for Sick Children (SickKids) in collaboration with Health Canada and Environment Canada.

“The research demonstrates that young children, pregnant women and people who are predisposed to develop allergic disease are particularly susceptible to the effects of traffic pollution,” says lead author Dr. Sharon Dell, Staff Respirologist and Senior Associate Scientist at SickKids. This, she notes, reinforces the importance of ongoing public policy debate related to the reduction of traffic-related air pollution.

The research team studied long-term exposure in a randomly-sampled, population-based study of nearly 1,500 children in Grades 1 and 2 who had lived in Toronto since birth. This was measured by tracking levels of nitrogen dioxide (NO2), which has previously been linked with childhood asthma. The children’s home, school and daycare addresses since birth were collected through telephone surveys in 2006. This data was used to derive estimates of cumulative NO2 exposures from birth to school age (five to seven years). This was the second phase of a larger study of more than 5,500 Toronto students.

While air pollution resulting from Toronto traffic congestion was found to be less intense than in other large cities, the harmful effects of traffic-related air pollution still triggered the onset of asthma in some children. NO2 exposure levels were generally below World Health Organization (WHO)-recommended maximum levels. Very few participants lived within 100 metres of a highway.

“This study establishes that even Toronto’s modest levels of air pollution resulting from traffic congestion may contribute to the development of asthma in school-age children,” says Dell, who is also Associate Professor in the Department of Paediatrics at the University of Toronto.

The researchers attribute this phenomenon to one or both of the following mechanisms: 1) traffic- related air pollution may boost allergic response in early childhood, so allergens could cause airway inflammation and airway hyperresponsiveness (easily triggered contraction of the small airways of the lungs) to develop, and 2) traffic pollution may increase the likelihood of airway inflammation upon exposure to allergens in children who have had a prior allergic response (food allergy, eczema, hay fever), leading to airway hyperresponsiveness and airway remodelling (permanent structural changes in the airway resulting from long-term inflammation). Early traffic-related air pollution exposure – around the time of birth – suggests that both mechanisms may be acting together.

“These findings are consistent with results of previous studies of major urban centres in other countries, which have already demonstrated similar harmful effects of traffic pollution,” says Dell. “Our research builds on this literature by evaluating the impact of exposures at different periods of a child’s life.”

According to the authors, the public health implication of their research is that infants, and potentially pregnant women, should be protected from potentially harmful exposures to traffic-related air pollution, particularly in combination with high levels of allergen exposure.

Future research in this area would measure potential ongoing effects of traffic-related air pollution in teens and adults.

The study is funded by Health Canada, Natural Resources Canada, Canadian Institutes of Health Research and SickKids Foundation.  

About The Hospital for Sick Children
The Hospital for Sick Children (SickKids) is recognized as one of the world’s foremost paediatric health-care institutions and is Canada’s leading centre dedicated to advancing children’s health through the integration of patient care, research and education. Founded in 1875 and affiliated with the University of Toronto, SickKids is one of Canada’s most research-intensive hospitals and has generated discoveries that have helped children globally.  Its mission is to provide the best in complex and specialized family-centred care; pioneer scientific and clinical advancements; share expertise; foster an academic environment that nurtures health-care professionals; and champion an accessible, comprehensive and sustainable child health system. SickKids is proud of its vision for Healthier Children. A Better World. For more information, please visit www.sickkids.ca.

For more information, please contact:

Matet Nebres
The Hospital for Sick Children
416-813-6380
matet.nebres@sickkids.ca

Suzanne Gold
The Hospital for Sick Children
416-813-7654, ext. 202059
suzanne.gold@sickkids.ca