Smog
aggravates asthma in children born prematurely or of low birthweight,
UC Berkeley researchers find
16
Nov 2000
By Catherine
Zandonella, Media Relations
EMBARGOED
FOR RELEASE UNTIL THURSDAY, NOV. 16, DATE OF PUBLICATION IN
THE AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE
Berkeley
- Smog-induced asthma symptoms are more severe in children
born prematurely or of low birthweight, according to a study
of 846 inner-city children conducted by researchers at the
University of California, Berkeley.
"The lower
the birthweight and the more premature the child was as an
infant, the greater the effect of pollution in triggering
asthma attacks," said Kathleen Mortimer, a UC Berkeley School
of Public Health epidemiologist and lead author of the study,
which appears today (Thursday, Nov. 16) in the American Journal
of Respiratory and Critical Care Medicine.
While researchers
have known that asthmatics often suffer more wheezing and
shortness of breath on days when air pollution levels soar,
they have been puzzled to see that the severity of symptoms
varies greatly from patient to patient. Mortimer and UC Berkeley
professor of epidemiology Ira Tager, working with colleagues
at Harvard Medical School and Case Western Reserve University,
went looking for reasons why some children might have more
severe reaction to air pollution than others.
The team
found that asthmatic children born more than three weeks prematurely
or weighing less than 5.5 pounds had a six-fold decrease in
breathing capacity on smoggy days as compared to full-weight,
full-term children. The children also reported a five-fold
greater incidence of symptoms like wheezing, coughing and
tightness in the chest.
Previous
studies have found that low birthweight and premature birth
are risk factors for asthma, but this study is the first to
show that air pollution aggravates asthma more severely in
such children.
"It is
a piece of evidence that has to be taken seriously," said
Tager. "This study demonstrates the short-term adverse consequences
of air pollution at relatively low levels."
Indeed,
it did not take a large jump in air pollution to provoke asthma
symptoms in the children. Less than five percent of the days
in the study, which spanned from the beginning of June to
the end of August, had air pollution levels that exceeded
federal standards.
"Our results
raise the question of whether the federal standards are sufficient
to protect sensitive subgroups like children born prematurely,"
said Mortimer. The study could help regulators establish air
quality standards targeted towards sensitive subgroups, rather
than blanket standards.
Approximately
five million, or seven percent, of children under age 17 suffer
from asthma nationally. Increased asthma symptoms translate
to more missed school days, more physician visits and more
hospitalizations, all of which can have significant financial
impacts.
The study
was part of a larger, multi-center study of inner-city children
aged four to nine who suffer from asthma. The children lived
in neighborhoods where at least 30 percent of resident had
incomes below the U.S. poverty line, and that were located
in eight urban areas across the nation: The Bronx and East
Harlem, N.Y.; Baltimore, Md.; Washington, D.C.; Detroit, Mich.;
Cleveland, Ohio; Chicago, Ill.; and St. Louis, Mo.
Because
all the children were from low-income neighborhoods, the study
could not examine whether socioeconomic status influenced
the children's response to air pollution. "There is no reason
to think this wouldn't hold up for all socioeconomic classes,"
said Tager, "but a study to confirm that should be done."
During
the study, Mortimer and her colleagues asked children to keep
daily records of symptoms such as wheezing, coughing and tightness
in the chest. Each child also measured his or her peak exhalation
flow rate by breathing into a measuring device each morning
and evening. The researchers interviewed parents to determine
which children were born prematurely or of low birthweight.
The researchers
compared the asthmatic symptoms to the average air quality
data gathered in each city by the U.S. Environmental Protection
Agency. Of the four pollutants measured by EPA (sulfur dioxides,
nitrogen dioxide, ozone and particulate matter of less than
10 micrometers in size or PM10), only ozone measurements were
available for all days in all eight urban areas, so ozone
levels were used as a marker for summer air pollution. Ozone
levels were stratified into 15 ppm increments and averaged
over five-day periods.
Only morning
symptoms were elevated during smoggy periods. Symptoms that
occur in the morning may be a more sensitive indicator of
a child's response to air pollution, said Mortimer, because
the children had not taken any asthma medication yet or engaged
in any strenuous activity that might have exaggerated the
effect.
The study
did not see any evidence that exposure to environmental tobacco
smoke influenced how the children responded to outdoor air
pollution. Mortimer said this might be explained by the fact
that the study was done during the summer, a time when children
generally spend less time indoors. "In the winter, we might
see a stronger effect from indoor sources," she said.
Mortimer
and Tager recently launched a study in Fresno, Calif. to document
the effects of air pollution on 450 asthmatic children over
a period of four years and to see whether their sensitivity
to smog changes as the children grow older.
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