NEW YORK - Competitive swimmers who train at indoor chlorinated swimming pools may have lung changes similar to those seen in people with mild asthma, a new study has found.
Researchers from France and Canada compared lung tissue and breathing tests from twenty-three elite Canadian swimmers, whose average age was 21, to ten mild asthmatics and 10 healthy, non-allergic people of the same age. Tissue samples and tests were taken during the off-season when swimmers were not competing.
The team, led by Valérie Bougault at the Lille 2 University of Health and Law in France, found that tissue samples taken from swimmers' lungs had nearly six times as many immune cells associated with asthma and allergies as the lung tissue of healthy subjects -- a similar amount to what was found in the group with mild asthma.
Swimmers and asthmatics also showed evidence of scar tissue in the lungs, while healthy non-swimmers did not.
"This study is the first to show direct evidence of airway damage associated with swimming in chlorinated pools," Alfred Bernard, a toxicologist at the Catholic University of Louvain in Brussels, Belgium, noted in an email to Reuters Health. Bernard was not involved in the study.
What these changes may mean remains unclear. "There's currently no evidence to suggest that these changes will lead to asthma down the line," Dr. Sally Wenzel, a pulmonologist at the University of Pittsburgh, told Reuters Health.
Lung tissue inflammation was not associated with actual asthma symptoms, such as coughing and wheezing, or with difficulty breathing during a medical test used to determine lung function.
However, previous research has linked exposure to swimming pool chemicals through water and air to respiratory allergies and asthma.
While acting as a disinfectant, chlorine reacts with a wide range of chemicals from human sweat, urine and hair, for example, to form chlorine byproducts -- some of which are hazardous to human health.
These byproducts are very volatile and can escape into the air above the water, according to Ernest Blatchley, an environmental engineer from Purdue University in West Lafayette, Indiana who specializes in water chemistry.
Competitive swimmers are known to inhale large amounts of these chlorine byproducts while doing strenuous exercise in the pool. Exposure to the chlorine compounds in indoor pools may make swimmers more sensitive to allergens such as pet dander, pollen and dust, wrote Bernard.
Indeed, roughly 50 to 65 per cent of competitive swimmers are sensitized to common allergens, compared to 29 to 36 per cent of people in the general population, wrote Bougault in an email to Reuters Health.
In the current study, published in the Journal of Allergy and Clinical Immunology, 18 of the 23 swimmers had at least one allergy. While exposure to allergens can cause changes to the lung tissue, "we found changes in the lung tissue of non-allergic swimmers as well," wrote Bougault.
This suggests that exposure to the chlorine byproducts themselves may be causing tissue damage, according to Bougault, who serves on the advisory boards for several major pharmaceutical companies, including GlaxoSmithKline and MerckFrosst, makers of the asthma medications Advair and Singulair.
The researchers cannot say for sure whether repeated exposure to swimming pool chemicals caused damage to the lung tissue. A previous study in elite cross-country skiers showed that the stress placed on lungs during high-level endurance sport training itself might be enough to induce airway changes.
While the effects of exposure to chlorine byproducts on the lungs remains unclear, it's likely the benefits of exercise outweigh potential risks posed by swimming in chlorinated pools, in those with or without asthma, according to Wenzel.
However, there are certain precautions that all swimmers can take at the pool to limit exposure to harmful chemicals, according to Bernard.
He suggested avoiding pools with a strong chlorine smell in the air -- a sign the chemicals in the pool are poorly managed.
One of the best things people can do to reduce exposure to harmful chlorine byproducts is to practice better hygiene, said Blatchley, even in so-called saltwater pools (which are not actually chlorine-free).
"Always taking a shower before entering a pool and not using it as a urinal can cut down on toxic byproducts," he said.