By Amy Norton

NEW YORK (Reuters Health) - Years of hard training may be to blame for the higher-than-average rates of asthma that are seen in elite swimmers, the results of a new study suggest.

The study, which compared teenage competitive swimmers with other adolescents, found that the young swimmers were no more likely than their peers to have airway hypersensitivity and respiratory symptoms suggestive of asthma.

The implication is that these problems in adult elite swimmers probably arise after years of training, the researchers report in the Journal of Allergy and Clinical Immunology.

High-level competitive swimming puts a high oxygen demand on the body, leading to hyperpnea, or abnormally deep and rapid breathing. This, along with chronic exposure to environmental irritants around the pool, such as chlorine, may lead to airway hyperresponsiveness -- a hallmark of asthma in which the airways excessively constrict in response to an environmental trigger.

"Exactly how fast and how much training is needed to develop these changes remains uncertain," Dr. Lars Pedersen, the lead researcher on the study, told Reuters Health.

Also unclear is which specific environmental factors or irritants may contribute to airway inflammation and asthma in elite swimmers, noted Pedersen, of Copenhagen University Hospital in Denmark.

He and his colleagues based their findings on assessments of 33 teenagers involved in elite-level competitive swimming, as well as 35 randomly selected teenagers and another 32 who had asthma.

They found no evidence that the swimmers had elevated rates of airway hyperresponsiveness. The young swimmers were no more likely than non-asthmatic teens to suffer from respiratory symptoms.

"This leads us to believe that elite swimmers do not have particularly susceptible airways when they take up competitive swimming when young, but that they develop respiratory symptoms, airway inflammation, and airway hyperresponsiveness during their swimming careers," Pedersen and his colleagues conclude in the report.

The next step, the researchers say, is to follow these teenage swimmers over time. "This will help us understand what happens to the airways during years of intense swimming with strenuous physical exercise and long-term exposure to chloride-containing gases in swimming pool arenas," they write.

Pedersen said that the findings also raise the question of whether elite athletes should be screened for airway hyperresponsiveness, since breathing problems alone are not enough to diagnose asthma in these athletes.

It's not clear whether airway damage resolves after swimmers end their careers, according to Pedersen. He noted, however, that one study found that airway hyperresponsiveness and inflammatory changes in elite swimmers may be partly, or even fully, reversible.

More studies, the researcher said, are still needed to answer this question.

SOURCE: Journal of Allergy and Clinical Immunology, August 2008.

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