Traffic pollution doubles allergy risk in children

A new study suggests that traffic pollution is to blame for increasing rates of allergy and atopic disease among kids by more than 50%.

The research was carried out at the German Research Center for Environment and Health at the Institute of Epidemiology, in Munich. The results are published in the June issue of the American Thoracic Society’s American Journal of Respiratory and Critical Care Medicine.

The researchers, led by Dr. Joachim Heinrich, found that exposure to pollutants from vehicle exhaust dramatically increased the risk of a child developing atopic diseases including hayfever, asthma and eczema.

The study showed that the closer children lived to roads the more likely they were to suffer from these conditions, with those living within 50 metres of a busy road having the highest probability of being affected.

Dr. Heinrich and his team examined almost 2,900 children at age four and more than 3,000 at age six to determine their rates of asthma and/or allergy which had been diagnosed by a doctor and how this correlated to their long-term exposure to traffic-related pollution.

All of the children in study lived in the Munich area and were enrolled at birth. Their exposure to traffic pollutants was calculated from the distance of their homes from major roads at birth and at two, three and six years of age. Air was tested for particulate matter (e.g., soot) and nitrogen dioxide (NO2) at each of forty identified points near high-traffic areas once each season between March 1999 and July 2000.

Parents were asked to complete questionnaires about their child’s respiratory diagnoses and symptoms, and their children were assessed for asthma, wheezing, sneezing and eczema. At six years of age, the children were also tested for food allergies.

The results showed significant positive associations between distance to the nearest road and asthmatic bronchitis, hay fever, eczema and allergic sensitizations. They also showed that the nearer a child lived to major roads the greater their chance of allergic sensitisation. Those living closest to major roads (within 50m) having a nearly 50% greater risk of allergic sensitisation.

These results were arrived at after the researchers took into account factors such as family history of allergies, pet ownership, and number of siblings, all of which are known to increase a child's risk of developing allergies.

“We consistently found strong associations between the distance to the nearest main road and the allergic disease outcomes,” said Dr. Heinrich. “Children living closer than 50 metres to a busy street had the highest probability of getting allergic symptoms, compared to children living further away.”

“[Children] living very close to a major road are likely to be exposed not only to a higher amount of traffic-derived particles and gases but also to a more freshly emitted aerosols which may be more toxic,” explained Dr. Heinrich in the journal article. “Our findings provide strong evidence for the adverse effects of traffic-related air pollutants on atopic diseases as well as on allergic sensitization.”

A large body of evidence from previous studies has linked pollution to allergic sensitisation. Estimates of pollutant exposure have been confused however by the fact that areas closer to major roads and high levels of pollution in cities tend also to be the poorer areas so any increase in allergy risk could be due to factors such as higher smoking rates among parents. Munich is the perfect location for a study such as this as major roads in the city are spread more evenly through both rich and poor areas thus minimising the impact of socioeconomic factors on the results.

A recent study found that the incidence of asthma in children is lower in areas with a greater number of trees. This finding is thought to be due to the ability of trees to take up pollutant gases and trap particulate matter.