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 researchers, led by Dr 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 - and a similar amount to what was found in the group with mild asthma.
No asthma risk down the line
Specifically, the swimmers had increased airway mucosa eosinophil and mast cell counts compared to controls, more goblet cell hyperplasia and higher mucin expression than controls or asthma patients and more submucosal type I and III collagen expression and tenascin deposition than controls.
"This study is the first to show direct evidence of airway damage associated with swimming in chlorinated pools," Dr Alfred Bernard, a toxicologist at the Catholic University of Louvain in Brussels, Belgium, noted in an email to Reuters Health. Dr Bernard was not involved in the study.
The implications of these changes are unclear, however. "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.
Swimming pool chemicals linked to asthma
Lung tissue inflammation was not associated with actual asthma symptoms in the athletes. 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 by-products, which are very volatile and can escape into the air above the water, according to Dr Ernest Blatchley, an environmental engineer from Purdue University in West Lafayette, Indiana who specialises in water chemistry.
Dr Bernard noted that competitive swimmers are known to inhale large amounts of these chlorine by-products 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, he said.
Lung tissue changes in non allergic swimmers
Indeed, roughly 50% to 65% of competitive swimmers are sensitised to common allergens, compared to 29% to 36% of people in the general population, Dr Bougault told Reuters Health by email.
In the current study, published online 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 lung tissue, "we found changes in the lung tissue of non-allergic swimmers as well," wrote Dr Bougault.
This suggests that exposure to the chlorine by-products themselves may be causing tissue damage, according to Dr Bougault, who serves on the advisory boards for several major pharmaceutical companies, including GlaxoSmithKline and MerckFrosst, makers of the asthma medications Advair and Singulair.
Exercise outweighs risks posed by pools
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 pulmonary stress during high-level endurance training might be enough to induce airway changes.
While the effects of exposure to chlorine by-products 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 Dr Wenzel.
However, there are certain precautions that all swimmers can take at the pool to limit exposure to harmful chemicals, according to Dr Bernard.
Avoid pools with strong chlorine smell
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 by-products is to practice better hygiene, said Dr 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.
By Lindsey Konkel
(Reuters Health, January 2012)