In what experts believe is the first study linking asthma to outdoor pools, girls who swam in outdoor pools were shown to be at greater risk for asthma, compared to those who swam in indoor pools.
A recent survey of 303 young swimmers (150 females, 150 males and
three unspecified) found that girls aged 9 to 12 who swim in
outdoor pools had a higher frequency of asthma than girls or boys
who swim in indoor pools only. As the number of hours spent
swimming in outdoor pools increased, so did the asthma frequency
among the girls. There was no significant difference among
This survey is the latest research showing a correlation between
swimming and respiratory problems, generally thought to be
associated with chlorine disinfection byproducts.
Mark Siegel, a fourth year undergraduate student at the University
of Wisconsin at Madison and former competitive swimmer, and Dr.
Charles Siegel, from the University of Missouri-Kansas City School
of Medicine, conducted the study. Overall, 30 percent of
respondents swam in outdoor pools only and 5 percent said they swam
in indoor pools only. The rest swam in both. All participants swim
in the Kansas City, Mo. area.
The rate of asthma among respondents was 19 percent, compared with
a national average of 9.2 percent, as reported in “Asthma in
America,” a survey conducted by research firm Schulman, Ronca
& Bucuvalas and funded by GlaxoSmithKline. However, because the
9.2 percent included infants who outgrow asthma, the swimmers may
be a skewed population, Siegel said.
He also noted that one possible reason outdoor pools showed a
greater correlation with asthma frequency may be that compared with
the indoor pools, which are mainly just used for competition,
outdoor pools in the Kansas City area are more likely to see
greater use, often for recreational purposes. That means greater
potential for disinfection byproducts because as those swimmers
shed organic compounds including sweat, or even urine.
Results were presented at the American College of Allergy, Asthma
& Immunology 2010 Annual Scientific Meeting, and published in
the Annals of Allergy Asthma and Immunology; however,
experts concur, more research is needed.
“I agree that competitive swimming indoors can create asthma,
but I find it difficult to believe outdoor pools are more of the
problem,” said aquatics expert Tom Griffiths, founder of
Aquatic Safety Research Group in State College, Pa. “We only
consider indoor pools as having ‘bad air.’ Still, it is
an interesting finding and we need to do more research on both
indoor and outdoor pools.”
Along with highlighting the need for greater understanding of how
DBPs affect swimmers in indoor and outdoor pools, this study also
calls into question the idea that swimming may be healthy for
“The question we always ask is: What is the best sport for
people with asthma? We’ve generally said that humidity and
warm air tends to be good for them, and we’ve often told our
patients to swim, but this study questions this advice,” said
John J. Oppenheimer, M.D., associate clinical professor of medicine
at New Jersey Medical School, and chairman of the ACAAI abstract
For his part Siegel said he’d like to partner with an
organization such as USA Swimming to survey a larger group.