But the researchers emphasize they are not suggesting anyone get out of the pool. "We do not say stop swimming," says researcher Manolis Kogevinas, MD, PhD, professor of epidemiology at the Centre for Research in Environmental Epidemiology in Barcelona. "We should keep a clear message that swimmers should keep swimming."
The research findings, he tells WebMD, are a message to the industry that ''the positive effects of swimming could be increased by reducing the chemicals."
Industry experts and pool researchers agree. "It's good that research is being done in this area,'' says Thomas Lachocki, CEO of the National Swimming Pool Foundation, an educational nonprofit organization based in Colorado Springs, Colo. The research is published online in the journal Environmental Health Perspectives.
Swimming and Health Risks: A Closer Look
''We have been doing research on chemicals in water -- not swimming pools [specifically] -- for quite some time," Kogevinas says. More recently, he and his colleagues have focused more intently on indoor swimming pool water. "Chemicals are produced when you put chlorine in water," he says. Chlorine reacts, for instance, to urine, cosmetics, and other substances typically found in swimming pools.
The researchers wanted to characterize these disinfection byproducts, or DBPs, in an indoor pool environment. Other studies have linked DBP exposure in drinking water to a risk of bladder cancer and other problems.
In the first of three new studies published in the journal, the researchers evaluated 49 healthy adults after they swam for 40 minutes in an indoor chlorinated pool, looking for biomarkers linked to cancer.
"What we found is by analyzing blood samples and urine samples, we have an increase in risk markers related to cancer," Kogevinas tells WebMD.
Exposure to the pool water was associated with a five-fold increase in one of the markers, he says. But that does not mean swimmers are doomed to get cancer, he stresses.
"This doesn't mean at all that swimmers have a five times increased cancer risk," he says. "It simply means that after swimming for 40 minutes in a chlorinated pool, you get an increase in this marker in the blood that in other studies has been associated with future cancer risk."
Swimming and Respiratory Effects
In a second study, Kogevinas and his colleagues focused on respiratory effects of exposure to indoor pool water.
"We compared markers of lung injury before and after swimming," he says, evaluating 48 swimmers this time, from the same group as in the first study.
They found changes in just one blood marker, a slight increase in one known as CC16. The increase, the researchers say, is due to the exercise itself in addition to the DBP exposure.
''Some studies have suggested a link with swimming and asthma ," Kogevinas says. "We found [only] one of many [respiratory] biomarkers [had] a small increase."
Swimming Pool Chemicals: What's in Pool Water?
In a third study, the researchers looked at water and air samples from two indoor pools. "We shipped them to the EPA [U.S. Environmental Protection Agency]," Kogevinas says. They found more than 100 DBPs in the pool water, some not identified before.
''Many are the same chemicals we find in tap water," he tells WebMD. "Some have been identified in experimental studies, animal studies, to be harmful."
The bottom line? "Pool water is not worse or better than tap water," he says, when it comes to byproducts. Only in the pool, he adds, "swimmers get a massive dose."
Swimming Pools and Health Risks: Second Views
Exerts from the swimming pool industry say research is crucial. "It's important we find ways to reduce exposure to potentially hazardous chemicals in pools," Lachocki says.
Even so, he calls the three studies "limited" because of some shortcomings. He wanted more information on how the pools studied were managed and what standards were used to keep the pools maintained.
"The question is, were the pools studied on the end of the spectrum of fabulously well taken care of, or not so fabulously?" he says.
The conclusion of the research that the pool water is no more hazardous than drinking water doesn't tell people if that is representative of most pools or just the ones studied, Lachocki says.
Another limitation is the small number of swimmers studied, he says.
What's a Swimmer to Do?
Lachocki agrees that no one should give up swimming as a result of the research. "Swimming continues to be ideal for an aging population and for a sedentary population," he says.
People who swim in indoor pools can check out the pool first, he tells WebMD. Ask, for instance, if the pool has certified operators, which means they have had training in how best to disinfect a pool.
His foundation trains certified operators. "There should be a certificate on the wall, showing the people who operate the pool are certified."
Swimmers can buy test strips, widely available at pool supply stores, and test the water themselves, he says. Swimmers can also ask the pool operators to show them the maintenance records proving the pool is maintained properly, he says.
Kogevinas suggests that people who swim in indoor pools follow rules, such as not urinating in the pool and showering before swimming.
By Kathleen Doheny
Reviewed by Laura Martin
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