The Canadian study, which surveyed more than 2,700 children in four cities across Canada, is the first to link air pollution and allergies in infants, according to Michael Brauer, the study's senior author.
"This study started by recruiting pregnant mothers in 2008. That continued until about 2012," Brauer told CBC News.
"The idea is to follow moms during pregnancy and the kids as they age, to look at the development of allergy and asthma in quite a detailed way."
Brauer, a professor in the School of Population and Public Health at the University of British Columbia, said the study did not find a link between mothers exposed to air pollution during pregnancy and allergy risk in their children, he notes.
Having pets lowers allergy risk
The study also found factors linked to lower allergy rates, including having:
- A cat or dog in their house.
- No attached garage on the house.
- Eating dairy products, eggs, nuts or grains during their first year.
- Attending daycare.
- Having older siblings in the house.
Sensitivity rates highest in Vancouver
The study also found Vancouver has the largest proportion of children developing a sensitivity to allergens — 23.5 per cent compared to 17 per cent in Toronto and Edmonton, and nine per cent in Winnipeg.
The higher rates in Vancouver were not linked to air pollution though, according to Brauer. Instead, other factors could be to blame, including the population's affluence, he said.
"We know that populations that tend to be wealthier tend to have higher rates of allergies. Allergy is something that we seem to link to more affluent lifestyles, globally. So there may be something going on there," said Brauer.
"Of course there's other things: the vegetation, food, lifestyles — other factors that may differ between Vancouver and the other cities."
Thousands of families monitored
The research was based on the Canadian Healthy Infant Longitudinal Development (CHILD) study , which is funded by AllerGen NCE and the Canadian Institutes of Health Research (CIHR).
The researchers used data from 2,477 children and assessed the children with skin allergy testing at approximately one year of age.
They were tested for sensitivity to 10 allergens, including cat, dog, dust mites, cockroach, fungus, milk, egg, soy and peanut, according to a statement released by UBC.
"Of the participants, 16 per cent of infants were sensitive to at least one of the tested allergens; 12.5 per cent were sensitive to a food allergen; and 5.3 per cent were sensitive to an inhalant allergen."
"Exposure to traffic-related air pollution was assessed by estimating nitrogen dioxide levels at each child's home address.
The researchers also evaluated the time each child spent away from home, including daycare attendance, and the use/type of the home's ventilation system."
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