Does Swimming in Chlorinated Pools Lead to Childhood Asthma?

Swimming Pool Attendance, Asthma, Allergies, and Lung Function in the Avon Longitudinal Study of Parents and Children Cohort

Font-Ribera L, Villanueva CM, Nieuwenhuijsen MJ, Zock JP, Kogevinas M, Henderson J
Am J Respir Crit Care Med. 2011;183:582-588

Study Summary

Concerns have been raised that regular swimming in chlorinated indoor swimming pools may lead to asthma and nasal symptoms in children, possibly because chlorine and related products are irritating to the respiratory mucosae. These concerns have been based on epidemiologic evidence^[1] and a body of observational studies. However, results of those studies have been inconsistent and inconclusive.

To throw a clearer light on the issue, a prospective longitudinal study (the best way to address the question) by Font-Ribera and colleagues was performed in the United Kingdom. Children were enrolled soon after birth. Respiratory symptoms were assessed by a standard questionnaire at regular intervals until aged 10 years. The questionnaire also inquired about the frequency of indoor swimming. At age 7, data were available for 5537 children; at age 10, the number was 4770 children. The frequencies of ever having had asthma, current asthma, the use of asthma medications, wheezing, and nasal or ocular allergies were the primary outcomes. Each of these was similar or lower in children with the highest exposure to indoor swimming compared with children who had little or no exposure to swimming. The odds ratio for asthma in children with high vs low swimming frequency at age 10 was 0.34 (95% confidence interval, 0.14-0.80). Lung function by spirometry, which was performed once at age 8, showed that frequent swimming tended to be associated with better lung function. Font-Ribera and colleagues concluded that, contrary to some previous studies, children who were regular swimmers had less asthma, better lung function, and were less likely to have nasal symptoms.

Viewpoint

This was a prospective birth cohort study and the largest and longest study of any kind to examine the risk for respiratory symptoms associated with exposure to potential irritants from indoor swimming. Although highly suggestive that swimming does not increase the risk of developing asthma or nasal symptoms, its limitations need to be considered. Children were, of course, not prospectively randomly assigned to swimming and nonswimming groups, so an element of self-selection may have unbalanced the groups. For example, children with a tendency for respiratory symptoms might have been disproportionately kept from swimming. Numerous other independent factors could have affected the outcome. Obvious factors include exposure to second-hand smoke, exposure to pets at home, and social class. The investigators statistically adjusted for many of these and other known risk factors, but one cannot be certain that the adjustment entirely eliminated the effects of these risk factors.

The study was conducted in the United Kingdom where, unlike many United States communities, public indoor swimming pools exist and swimming year-round is possible, if not mandatory, for all school children. Thus the prevalence of swimming in this study was very high in comparison with other studies. Moreover, the level of chlorine and chlorine-related chemicals used in the pools varied and could not be controlled. These limitations notwithstanding, it seems safe to say that regular swimming in indoor pools is not a risk factor for the development of asthma or other respiratory problems in children up to the age of 10. Indeed, to the contrary, children who swim regularly may even obtain some protection from asthmatic and allergic-type respiratory disorders.

Abstract

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