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Asthma PrevalenceNumber of people ever told by a health professional that they had asthma.

Results from a new study support a growing body of research that suggests a link between chlorinated pools and asthma. Also, for the first time it extends that link to all respiratory allergies.

The findings — published in September in an online edition of the journal Pediatrics — show that teenagers who swam in chlorinated pools (indoors or outdoors) faced a significantly greater risk of having asthma. They had more than eight times greater risk of asthma than teens who frequented pools with copper-silver disinfecting systems.

“With this new study, our previous research and that of others, and the results from our ongoing studies based on lung injury biomarkers, there is now very little doubt that the irritating effects of chlorine and its byproducts can promote the development of allergic diseases in sensitive subjects,” said study author Dr. Alfred Bernard, a professor of toxicology and research director at Catholic University of Louvain in Brussels, Belgium. “For recreational swimmers such as those examined in our study … it is a question of excessive levels of chlorine in the water or in the air just above water surface, and of some genetic predisposition.”

The study included 847 Belgian adolescents ages of 13-18. Researchers compared the health of the majority of the group, 773 teens who swam in chlorinated pools, with a “control” group of 114 teens, who swam mostly in aquatics facilities sanitized with copper-silver systems. The odds of asthma or respiratory allergies increased with longer exposure.

Bernard said this study is significant for several reasons, including “the fact that for the first time we had access to a reference population [swimmers in the copper-silver pool] who had almost never attended chlorinated swimming pools, and the fact that for the first time we considered the total chlorinated pool attendance, combining the attendance at indoor and outdoor pools.” Also, the sample population of teens was larger than in previous research.

But not everyone is ready to accept the hypothesis that chlorine causes respiratory problems as a fact.

“The new study by Bernard et al. should be evaluated carefully along with other data on pools and respiratory health,” cautioned Jeffery Sloan, senior director, water and sustainability at the Chlorine Chemistry Division of the American Chemistry Council. “Other research has not shown a consistent association, much less a conclusive link between chlorinated pools and childhood asthma.”

Sloan added that proper disinfection is essential to maintain healthy water and that “in well-managed swimming pools, chlorination byproducts are expected to pose little risk to health.”