Vancouver tops four Canadian cities for child allergies, UBC study finds

Exposure to other kids and pets lowered risk

Early results from a study following thousands of Canadian kids from in utero to kindergarten support the theory that germ-free environments are contributing to rising allergy rates.

Tests conducted on 2,477 one-year-olds in Vancouver, Edmonton, Winnipeg and Toronto found that children who came into contact with more microorganisms - from germy kids or furry pets - were less likely to have a sensitivity to either food or air-borne allergens.

"It looks as though kids who attended daycare or had older siblings were less likely to develop allergies and that's consistent with them being exposed to more infections, more viral infections, in their life," said Michael Brauer, the study's senior author and a professor in the School of Population and Public Health at the University of British Columbia.

"One way to think about the development of allergies is that if you live in a very sterile environment, your immune system may become more allergic. Whereas if you're exposed to more diversity - it could be infections or all kinds of microbes because of animals around you - you're less likely to become allergic."

Brauer's findings, published Monday in the journal Environmental Health Perspectives, is based on information collected in the six-year, $12-million Canadian Healthy Infant Longitudinal Development (CHILD) Study into how genetics and the environment affect asthma and allergies in children. The massive project first approved in 2007 followed more than 3,500 families in the four cites, starting from the time a mother was pregnant to that child's fifth birthday. Researchers across the country are shifting through a mountain of information collected from allergy tests, blood and feces samples and home inspections.

Children in the Vancouver portion of the study are now between the ages of three and six so data collection here will continue for two more years.

Today's study revealed that participants in Vancouver had a higher rate of sensitivity to airborne allergens than in other cities, something Brauer says he can't explain.

Across the country, 132 oneyear-olds had a reaction to tests in which a minuscule amount of an allergy-causing substance was inserted under their skin with a pin prick. Fifty-five of those kids were in Vancouver, making up 42 per cent of the total. Toronto was a distant second with 21 per cent of the total. They reacted to mould, cat and dog hair, dust mites or cockroach droppings - all typically airborne.

Brauer is a specialist in air pollution and its effects on human health and his team found evidence that exposure to contaminants from heavy car traffic during the first year of life increased the chances of developing allergies to food, mould, pets and pests. No link was found if mothers were exposed while pregnant.

Researchers estimated the amount of nitrogen dioxide - a key contaminant in car exhaust - near the children's homes and also calculated their exposure based on time spent at home or at daycare.

Dr. Stuart Turvey, a pediatrician at BC Children's Hospital and a professor in UBC's Faculty of Medicine, tested children in the study. He says the findings on air pollution should be a reminder that the environment is a key factor in everyone's health.

"It adds to the ongoing weight of evidence that we can't be complacent about these things. We think of Vancouver as a healthy, clean-air city, but there still seems to be a signal here," said Turvey.

"We're seeing this massive rise in allergic disease over the last three or four decades - really one or two generations - and if we think about what's changed, our genetic structure isn't very different, but the environment in which children are growing up is different for a variety of reasons."

There is more air pollution, for instance, but fewer childhood infections because of antibiotics and improved hygiene. Stress also plays a role in allergies and may be higher in today's society, he added.

"The good news is, we can't change our genetics, but there's a lot we can do about the environment."

Across all cities, 12.5 per cent of one-year olds showed a reaction to cow's milk, egg white, soybean or peanut based on skin prick tests.

Brauer noted that caution should be used when interpreting the findings because participants volunteered for the lengthy and invasive study. That tends to attract people with higher educations and incomes. More than 90 per cent of mothers in the study had some university or college education and did not smoke. Sixty-one per cent had an allergy themselves.

Overall, 400 - or 16 per cent - of the 2,477 infants had a reaction to at least one of the 10 allergens tested, a figure that proves most Canadians are directly or indirect affected "by this epidemic in allergic disease," said Turvey.

Kids with no allergies were more likely to have eaten dairy products, eggs, nuts, peanuts, grains and processed cereals during the first year of their life and to live with a cat or dog.

Children whose mothers have an allergy were also more likely to also have one.

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