Swimming in Indoor Pools Linked to Asthma Risk

Laurie Barclay, MD

May 29, 2003

May 29, 2003 -- Swimming in indoor pools is associated with increasing risk of asthma, according to the results of a study published in the June issue of Occupational and Environmental Medicine.

"Regular attendance at chlorinated pools by young children is associated with an exposure dependent increase in lung epithelium permeability and increase in the risk of developing asthma, especially in association with other risk factors," write Alfred Bernard, from the Catholic University of Louvain in Brussels, Belgium, and colleagues.

The trigger seems to be trichloramine, or nitrogen trichloride, a highly concentrated volatile by-product of chlorination, which is readily inhaled and generated during contact between chlorine and urine, sweat, or other organic matter.

In a three-part study, the investigators first measured levels of lung proteins (serum alveolar surfactant-associated proteins A and B [SP-A and SP-B], 16 kDa Clara cell protein [CC16]) and IgE in sera of 226 healthy primary school children from rural and urban schools. Since early childhood, these children had swum regularly at indoor chlorinated pools weekly or every other week.

To evaluate the immediate effects of trichloramine, Dr. Bernard's group also analyzed sera from 16 children, aged 5 to 14 years, and 13 adults, aged 26 to 47 years, before and after swimming in an indoor pool. The group also assessed the prevalence of childhood asthma, using data from a survey done between 1996 and 1999 of 1,881 children aged 7 to 14 years.

The best predictor of lung epithelium permeability was cumulated pool attendance, which correlated with serum SP-A and SP-B. Although serum IgE was unrelated to pool attendance, it was positively correlated with lung hyperpermeability as measured by serum SP-B.

In children and adults attending an indoor pool, serum SP-A and SP-B increased significantly after one hour at poolside without swimming. Cumulated pool attendance significantly correlated with exercise-induced bronchoconstriction test and total asthma prevalence. For children who swam the most frequently, lung damage was equivalent to that found in regular smokers.

"We therefore postulate that the increasing exposure of children to chlorination products in indoor pools might be an important cause of the rising incidence of childhood asthma and allergic diseases in industrialised countries," the authors write, while recommending further epidemiological studies. "The question needs to be raised as to whether it would not be prudent in the future to move towards non-chlorine based disinfectants, or at least to reinforce water and air quality control in indoor pools in order to minimise exposure to these reactive chemicals."

AstraZeneca has provided a grant to one of the authors.

Occup Environ Med. 2003;60:385-394

Reviewed by Gary D. Vogin, MD


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