linked to prevalence of allergic rhinitis and asthma
– Studies from Taiwan and Germany show that respiratory problems
in children appear to be induced rather than exacerbated by air
pollution caused by heavy traffic.
The studies appear in the June edition of the European Respiratory
Journal. The two independent studies looked at almost 300,000
children in total.
The larger study, carried out in Taiwan, used data from 800 schools.
The eight-month study involved adolescents ages 12 to 15 years.
The Chinese version of the standard International Study of Asthma
and Allergies in Childhood questionnaire was sent to more than a
million students and their parents. Only students from non-smoking
homes were ultimately included in the study.
While doctors had already diagnosed allergic rhinitis in 28.6% of
boys and 19.5% of girls in that group, the questionnaire responses
indicated the rates were much higher, at 42.4% of boys and 34% of
In parallel, the Taiwanese team examined data provided by the 55
air monitoring stations in the areas in which the schools were located.
The hourly sampling data from the stations identified two main types
of pollutants: first, those connected directly with vehicles, namely
nitrogen oxides, carbon monoxide and ozone; and, second, pollutants
emitted by industry, power plants or domestic fossil fuels, especially
sulphur dioxide and particulate matter
with a diameter of 10 microns or less, the so-called "PM10."
The team identified a clear connection (with an increased risk of
16% for girls and 17% for boys) between carbon monoxide or nitrogen
oxides in ambient air and the prevalence of medically diagnosed
allergic rhinitis, after adjustment for climatic factors (temperature
and humidity) that also represent risk factors.
However, the Taiwanese researchers could not determine the respective
role of each pollutant because certain other traffic-related pollutants
were not measured.
For allergic rhinitis diagnosed on the basis of the questionnaire
responses, the figures for increased risks were slightly lower at
12% and 9%, respectively.
"While more boys than girls seem to suffer from allergic rhinitis
in the general population, traffic pollution seems to have the same
impact on both sexes," said Dr. Leon Guo, the lead author of the
The much smaller German study, involving 4,000 children who lived
within 50 m of a busy roadway in Munich, compared child health data
with traffic density and levels of certain pollutants.
Traffic-related air pollution (levels of benzene, soot and nitrogen
dioxide) was calculated according to a prediction model on the basis
of measurements taken at 34 measurement sites in the city, of which
16 had a daily flow of between 17,000 and 33,000 vehicles and the
remaining 18 had a flow exceeding 33,000.
Here, as in a previous study, a geographical information system
was used to identify where each child's home was situated in relation
to street segments, at distances of up to 50 m and between 50 m
and 300 m.
level of the air pollutant exposure was then calculated for each
child according to the model created from the site measurements.
Children living within 50 m of very busy roads (with a flow of more
than 33,000 vehicles per day) were almost twice as likely to suffer
from asthma as the general population (a relative risk of 1.8).
The figures were lower for coughing and wheezing, for which the
relative risk was 1.6. Allergy susceptibility was also increased
(by between 17% and 56% depending on the allergen), particularly
in children who were also exposed to tobacco smoke.
Since the effect appeared to fall off with distance, the researchers
emphasize that their figures also suggest a dose-response effect.
An editorial in the journal, written by Bert Brunekreef of the University
of Utrecht, and Jordi Sunyer of the Medical Research Institute of
Barcelona, struck a cautious note. "Surely," they wrote, "the world
variation in the prevalence of asthma is so large that it seems
unlikely that traffic-related air pollution is a major determinant
of this variation. Nevertheless . . . we are gradually seeing more
data suggesting that . . . air pollution may not just be a factor
triggering attacks in patients who have developed asthma already."