Young children living close to busy roads are at increased risk of developing asthma or ear, nose and throat (ENT) infections, and are more sensitive to food allergens, concludes a major study published in the forthcoming issue of the European Respiratory Journal (ERJ). This original study monitored over 4,000 Dutch infants from birth to the age of four and assessed their level of exposure to airborne pollutants on the basis of where they lived.

Asthma has increased sharply throughout the industrialised world in the last thirty years and, according to the World Health Organization, is now the most widespread chronic condition affecting children. While the reasons for this "epidemic" have not yet been completely explained, various environmental factors are increasingly coming under suspicion, road traffic pollution in particular. This was the focus of the international team whose results are published in the forthcoming issue of the ERJ.

"Although many studies have certainly demonstrated that airborne pollution could exacerbate existing asthma, it is not so certain that such pollutants could really cause the onset of infant asthma or atopy," explains, by way of preamble, the main author, Michael Brauer, of the School of Occupational and Environmental Hygiene, University of British Columbia, Vancouver, Canada.

To investigate this, Brauer and colleagues from the Netherlands universities of Utrecht, Rotterdam and Groningen and the National Institute for Public Health and the Environment, applied an original method to analyse data obtained from a large prospective cohort of Dutch infants.

Focus on location of the home

Known as PIAMA (Prevention and Incidence of Asthma and Mite Allergy), the cohort study covered 4,146 infants recruited before birth, during the second trimester of their mother's pregnancy, in various areas of the Netherlands.

In addition to the classical data obtained either from health questionnaires completed by parents or from blood tests, the team assessed each subject's level of exposure to traffic fumes on the basis of where the child lived. This is what makes the study truly original.

To assess the level of exposure, Brauer and his team tested forty sites, measuring three variables: nitrogen dioxide, particulate matter (PM 2.5) and soot from diesel emissions.

Then, using a mathematical model incorporating a geographic information system (GIS), the researchers were able to estimate each child's level of pollutant exposure at the home location.

Where a family moved houses, the team used the address at the time of the child's birth to calculate exposure levels in very early infancy.

Asthma and infections up by 20-30%

Four years down the line, Michael Brauer can see higher rates of asthma, wheezing, ENT infections, colds and flu in children living near busy roads.

The relative risk of these symptoms is multiplied by 1.2 or 1.3, which confirms results obtained by the same team when the children were two years old.

Moreover, the researchers found that children with the highest pollution exposure, whose blood was tested for immunoglobulin E (IgE) levels, demonstrated hypersensitivity to food allergens. Brauer concedes, however, that the consequences of this hypersensitivity (not necessarily synonymous with food allergy at this age) need further investigation.

Indeed, a further study of this cohort is already under way, to be completed when the children reach the age of eight.

Groundbreaking study

"This study provides clear evidence of the long-term effects of pollution on young children and shows the importance of reducing exposure levels in early infancy and even during pregnancy. Regulating emissions from car exhausts is essential, but it is even more crucial to keep major traffic arteries away from areas where people live and work," Brauer emphasises.

This study is a major contribution, according to Michael Jerrett, Associate Professor in Public Health at the University of California, Berkeley, USA, whose editorial appears in the same issue of the ERJ. The results "have increased certainty that air pollution contributes to the development of lung disease in children."

Jerrett pays tribute to the study's thoroughness and original methodology, with longitudinal monitoring of the cohort and extended modelling of the subjects' pollutant exposure.

And, picking up on one of the main lessons to be drawn from Brauer's work, namely the damage pollution can cause to babies even before they are born, he recalls that the damage continues beyond infancy and affects lung development into adolescence.

"This study fills a number of gaps in the existing scientific literature," Jerrett concludes.

"Air pollution and development of asthma, allergy and infections in a birth cohort"
European Respiratory Journal (ERJ)