For the study, a Mexican team led by Dr Isabelle Romieu of the Institute Nacional de Sauld Publica, correlated pollutants associated with exacerbation of respiratory symptoms in asthmatic children.
Earlier studies suggest that traffic pollution, and diesel particles in particular, originating from motor vehicles in the cities, may have a greater effect on respiratory health than other pollutants.
Till date, no studies have clearly linked different types of vehicular traffic exhaust to respiratory health of either asthmatic or healthy children.
In the study, the researchers recruited 147 asthmatic children and 50 non-asthmatic children, between the ages of 6 and 14, through a pediatric hospital in Mexico City.
Parents kept a daily record of coughing and wheezing experienced by their children, as well as medication usage. In the course of the study, the researchers also recorded the atmospheric levels of the pollutants ozone, nitrogen dioxide and diesel particles in Mexico City.
The amount and type of traffic in areas inhabited by the volunteers was also recorded in order to evaluate whether diesel-fuelled vehicles had a greater impact upon respiratory health than pollution from other vehicles.
The scientist observed that in asthmatic children, coughing, wheezing and medication usage was linked with increased levels of atmospheric pollutants. In healthy volunteers, increased coughing was only seen with higher levels of nitrogen dioxide. Children living in areas with high levels of traffic more often experienced worsening of asthma symptoms and greater use of medication.
Also, small buses for public transport running on petrol/natural gas, and larger buses and trucks running on diesel, were more strongly associated with worsening of symptoms.
While oxidative stress is considered to be a major underlying feature of the toxic effect of air pollutants, there is still a need for a better understanding of the actual mechanisms by which pollutants cause exacerbation of respiratory symptoms.
Romieu claimed that, all types of traffic exhaust have an adverse effect on children respiratory health and that given the proximity of many schools to roads with heavy traffic, "these results have significant implications for public health policy within cities in Mexico and the rest of the world".
The study is published in BioMed Central's open access journal Respiratory Research.