Swimming Pools May Increase Childhood Asthma Risk
In this entry, I would like to provide a little background and updated information on the association between swimming in chlorinated pools and asthma in childhood. Compared to the attention that allergies, exercise, and other environmental factors have received regarding their association with asthma, pool chlorine has not been in the "forefront" of this discussion. However, the idea that chlorinated pool exposure may be associated with the increase in asthma seen in the past few decades is not new. In fact, the term "chlorine pool hypothesis" exists in the scientific literature to explain a possible contributor to the recent increase in asthma.
The association between chlorinated pool exposure and asthma
The idea that pool exposure could account for the recent increase in asthma comes from the fact that this increase has occurred too quickly to be explained by a change in the genetics of asthma alone. The observation that asthma seemed to occur more frequently in children exposed to chlorinated pools was followed by well designed studies to address this question directly. These early studies focused on indoor pool exposure, based on the premise that indoor pools are less well ventilated and would lead to more concentrated exposure.
One study sought to correlate the amount of time spent in indoor pools in childhood to the presence of asthma at age 10-13. The investigators found that asthma was more common in children who had spent a significant amount of time swimming in a pool than kids who hadn't or had swum little. In addition, pool attendance was correlated with certain laboratory markers of asthma. As other typical predictors of asthma, such as having asthma in close family members and allergies, correlated with asthma, the investigators concluded that swimming in a pool was not a predictor of asthma alone, but that pool exposure interacted with other risk factors to promote asthma development.
To see whether this effect would be present in an environment with better ventilation, investigators recently performed a similar study in children exposed to outdoor pools. Interestingly, the results were similar, suggesting that decreased ventilation in indoor pools was not a major factor in putting children at risk for the effects of exposure to chlorinated water. Once again, the authors concluded that other asthma risk factors were interacting with pool exposure to predispose children to having asthma.
The recent evidence that associates pool exposure, both indoors and outdoors, with asthma is cause for further examination. It seems fair to conclude that there is an interaction between being at risk for developing asthma (e.g. having allergies) and exposure to chlorinated pools. Taking a step back, however, one needs to ask why this longstanding pastime has only recently ‘come to court' as a cause of asthma. Has there been a significant increase in attending pools over the past few decades amongst kids? For comparison, there is no question that the increase in elbow tendonitis seen in the late 1970s was associated with many more amateurs playing tennis, hence the term ‘tennis elbow'. Have we seen a similar increase in pool attendance? While I am not sure, there is no question that swimming is not only good exercise for kids but a lot of fun. It seems premature at this point to say that children should not swim in pools to prevent the development of asthma. However, children who have asthma or allergies may be sensitive to swimming in chlorinated pools, and parents should discuss strategies to detect this potential sensitivity with their child's care provider. For some children, finding natural water to enjoy swimming may be a better alternative.