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Although particulate air pollution has been blamed for a
wide variety of negative health effects, a three-year study of
asthmatic children in Denver, published in the November Journal
of Allergy and Clinical Immunology, indicates that it
does not lead to significant worsening of asthma during the
pollution-heavy winter months. Upper respiratory infections,
however, were associated with a significant decline in lung
function, asthma symptoms and asthma exacerbations.
"In our study, wintertime air pollution had no significant
effect on asthma exacerbations or lung function," said Nathan
Rabinovitch, M.D., a lead author of the study and
pediatric allergist at National Jewish Medical and Research
Center. "Upper respiratory infections, however, doubled the
chances that a child would suffer an asthma exacerbation and
more than quadrupled the odds that a child would suffer asthma
symptoms."
The study monitored 41, 63 and 43 elementary school
children during three successive winters in Denver, Colorado,
when particulate pollution is worst. The children, aged 6 to
12 years, were mostly urban minority children with moderate to
severe asthma. Dr. Rabinovitch and co-investigator Erwin
Gelfand, M.D., Chairman of Pediatrics at National Jewish,
monitored several health outcomes in the children, including
asthma exacerbations, visits to emergency rooms and
hospitalizations. They also monitored the children's lung
function, medication use, asthma symptoms, and whether they
had upper respiratory infections.
The researchers correlated those health measures with daily
variations in six air pollutants: particulates less than 10
microns in diameter, particulates less than 2.5 microns
diameter, carbon monoxide, nitrogen dioxide, sulfur dioxide
and ozone. In general pollutants were comparable to levels
found in most large American cities.
As expected, the raw data did show worse health associated
with high pollution days. But when the researchers controlled
for potential time-related confounders, such as upper
respiratory infections, the correlation disappeared on almost
all measures. Higher carbon monoxide levels were marginally
associated with increased use of rescue medications (odds
ratio: 1.065) and daily symptoms were marginally associated
with ozone levels (odds ratio: 1.083).
"It is well known that upper respiratory infections can
cause problems for people with asthma, but the air pollutions
results were a surprise," said Dr. Gelfand. "We believe that
careful monitoring of the children allowed us to filter out
confounding factors that would have mistakenly suggested a
significant health impact of air pollution."
The researchers are not ready to write off the effects of
air pollution during summer. For one, children may be exposed
to higher levels of air pollution in the summer because they
spend more time outside. Also, ozone, a known respiratory
irritant, rises to much higher levels during the summer and
may pose more of a problem than particulate pollution in the
winter. Next summer Drs. Rabinovitch and Gelfand will begin a
study of the health impacts of ozone on children with
asthma.
"We believe this is good news for parents of children with
asthma," said Rabinovitch. "Instead of worrying about air
pollution they can focus their efforts on preventing and
treating the real wintertime threat to their children's health
- colds and other respiratory infections."
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