Swimming pools and asthma, how much is safe?

There is reasonable evidence that swimming in chlorinated pools causes asthma in elite swimmers. The one longitudinal study showed increasing asthma (and methacholine reactivity and sputum eosinophilis) after 5 years in those who continued competive swimming from the Finnish national team, and a reduction in those who quit competive swimming.

There is evidence in children and adults that indoor pool environments causes an immediate rise in sufactant proteins (SPA and SPB) and that this starts when in the pool environment before entering th water. Occupational asthma is reported in pool attendants and teachers who do not enter the water, nitrogen trichloride has resulted in immediate asthmatic reactions on specific challenge testing showing that it is not the dissolved chlorine in the water (as hypochlorite ion) but the chloramines in the air above the pool that are the main culprit. There are a series of cross-sectional studies of Belgian school children showing a relationship between cumulative hours spent in chlorinated pools and asthma, the low chlorine pool group however come from a socially advantaged group who mainly swim in a pool with copper-silver water treatment, raising the question of confounding variables.

The risks of children swimming has been clarified in the first longitudinal study of swimming and asthma from the Avon (Bristol UK) birth cohort study which has measured swimming attendance and asthma onset from birth to aged 10. This showed no increase in asthma in the swimmers, including those swimming under aged 4. Lung function increased slightly with swimming.

So swimming recreationally in children does not increase asthma, high level competitive swimming does. Where the risk starts is unknown, but the chloramines in the air above the water are the most likely cause and as much attention is needed to the pool air as the water.

References

	Font-Ribera L, Villanueva CM, Nieuwenhuijsen MJ, Zock J, Kogevinas M, Henderson J, Swimming Pool Attendance, Asthma, Allergies and Lung Function in the ALSPAC Child Cohort, Am J Respir Crit Care Med, 2011;183:582-588,

	Bernard A, Nickmilder M, Voisin C, Sardella A, Impact of chlorinated swimming pool attendance on the respiratory health of adolescents., Pediatrics, 2009;124:1110-1118,

	Bernard A, Nickmilder M, Voisin C, Outdoor swimming pools and the risks of asthma and allergies during adolescence, Eur Respir J, 2008;32:979-988,

	Bernard A, Carbonnelle S, Michel O, Higuet S, de Burbure C, Buchet J-P, Hermans C, Dumont X, Doyle I, Lung hyperpermeability and asthma prevalence in schoolchildren: unexpected associations with the attendance at indoor chlorinated swimming pools , Occup Environ Med, 2003;60:385-394,

	Helenius I, Rytilä P, Sarna S, Lumme A, Helenius M, Remes V, Haahtela T, Effect of continuing or finishing high-level sports on airway inflammation, bronchial hyperresponsiveness, and asthma: A 5-year prospective follow-up study of 42 highly trained swimmers, J Allergy Clin Immunol, 2002;109:963-968,

	Thickett KM, McCoach JS, Gerber JM, Sadra S, Burge PS, Occupational asthma caused by chloramines in swimming-pool air, Eur Respir J, 2002;19:827-832,

	Hery M, Hecht G, Gerber JM, Gendre JC, Hubert G, Rebuffaud J, Exposure to chloramines in the atmosphere of indoor swimming pools, Ann Occup Hyg, 1995;39:427-439,

	Pickering CAC, Mustchin CP, "Coughing water", bronchial hyperreactivity induced by swimming in a chlorinated pool, Thorax, 1979;34:682-683,

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