Allergic children living in affluent
countries were four times as likely to have the lung condition as their
non-sensitized counterparts; in non-affluent countries, children with
allergic responses were only 2.2 times as likely to have asthma.
The
global research study is based on 54,000 parental assessments of their
children's respiratory symptoms, gleaned through standardized
questionnaires. The children studied were between eight and 12 years
old.
Researchers also evaluated 31,000 skin-prick tests and
analyzed the serum levels of allergen-specific IgE in nearly 9,000
children from 22 countries, from rural Africa to urban Europe.
The
allergen-specific IgE antibody test screens for an allergy to a
specific substance or substances when a person suffers from
allergy-like symptoms.
Researchers then assessed how the severity
of allergic sensitizations and asthma symptoms of a given country were
connected to its gross national income per capita.
"We observed
large variations in the prevalence of asthma symptoms and of atopic
sensitization (allergic sensitivity) among populations," Dr. Gudrun
Weinmayr, one of the study's authors, said in a release.
"The
association between current wheeze, an indicator of asthma, and skin
prick sensitivity, an indicator of allergic reaction, was strong in
virtually all affluent countries, but much weaker in less affluent
settings."
The study's authors theorize that local environmental
factors may affect asthma and allergy rates in different ways. And they
speculate that developed countries may have more cases of
allergy-induced asthma while less-affluent nations have more cases of
non-allergic asthma in children.
They also believe that some of
the factors that prevent children from developing asthma may be absent
in more affluent countries. "A wide range of different factors,
including nutrition, microbial and allergen exposure, housing
conditions, and exposure to pollutants, and so forth may have played a
role," reads the report.
According to a 2006 report by the
Montreal-based Commission for Environmental Co-operation, asthma rates
among children in some parts of North America are four times higher
than they were 20 years ago.
It found that in Canada, about 20 per cent of boys and 15 per cent of girls aged eight to 11 have been diagnosed with asthma.