Dutch researchers have uncovered elusive evidence of a direct link between air pollution and children’s asthma symptoms by first identifying groups at risk, such as children with allergies.
In research done at Groningen University, which was published last week (Lancet 1999;353:874-8), children with both bronchial hyperresponsiveness and atopy, a susceptibility to allergens measured by higher concentrations of IgE antibodies, were for the first time compared with children from control groups.
The researchers found that as concentrations of particulate matter and gases from car exhaust such as sulphur dioxide and nitrogen dioxide increased, the study children were significantly more likely to experience lower respiratory symptoms.
The effects on the study children were comparable with those on children who already had chronic respiratory symptoms. There was no measurable effect on the children who had neither condition.
Data were collected from 459 children aged 7 to 11 during three winters from 1992 to 1995. The children were given a diary in which they recorded respiratory symptoms every day for three months; they also recorded lung capacity through peak expiratory flow measurements taken three times a day.
Atmospheric concentrations of particulate matter of less than 10 μm in diameter, black smoke, sulphur dioxide, and nitrogen dioxide were continually measured.
The results showed that for children with both bronchial hyperresponsiveness and atopy, lower respiratory symptoms such as attacks of wheezing and shortness of breath increased by between 32%and 139%for each 100 μg per cubic metre increase in particulate matter. For every 40 μg per cubic metre increase in black smoke, sulphur dioxide, or nitrogen dioxide there was an increase of between 16%and 131
Although air pollution is regarded as a possible cause of the more than doubling of asthma cases in the past 30 years, evidence of an effect of air pollution on children’s health has so far been inconclusive (BMJ 1996;312:649).
But Dr Marike Boezen from Groningen University explained that unlike in other studies, her team had taken a step back at the start of their study and characterised children according to features that would make them prone to respiratory symptoms.
“If you want to study air pollution you must try to focus on identifying susceptible groups. There are no really measurable health effects on children who are not allergic.”
Figure.
Pollution exacerbates respiratory symptoms in susceptible children