Effect of competitive swimming on airway inflammation: A 3‐yr longitudinal study

To the Editor, In recent years, the observation that regular pool attendance, especially by young children, was associated with lung hyperpermeability and increased risk of developing asthma led to the ‘pool chlorine hypothesis’ (1). Accordingly, the increasing and largely uncontrolled exposure of young children to chlorination byproducts contaminating the air of indoor swimming pools could contribute to the childhood asthma rise in industrialized countries (1). Moreover, an increasing body of literature suggests an association between competitive swimming and asthma (2). A higher prevalence of asthma and asthma-like symptoms has been identified in elite swimmers. Environmental exposures, mechanical stress to the airways, increased prevalence of respiratory infections and dysautonomia, have been recognized as asthma contributory factors (2). Increased numbers of both eosinophils and mast cells were observed in bronchial biopsies of competitive adult swimmers, leading to believe that airway inflammation and hyper-responsiveness develop during the training career (3). While the latter seems to be a transient phenomenon (4), whether airway inflammation persists is still debated (5–7). Therefore, we aimed to assess changes in airway inflammation of swimmers during a 3-yr follow-up. Competitive non-elite young swimmers from the two main Portuguese swimming teams were invited (n = 120) to participate in this cohort prospective study. Informed consent was obtained from 105, which were assessed at the baseline visit. From these, 86 attended the 3-yr follow-up visit and were included in the final analysis. No significant differences were observed between the 19 lost to follow-up subjects and the remaining (Table 1). ‘Active swimmers’ were defined as those remaining at high level of competitive swimming; those who quitted at least 6 months before the follow-up visit were considered ‘past swimmers’. None of the subjects smoked. The local hospital ethical committee approved the study. Subjects completed a self-administered questionnaire, including questions from the ISAAC questionnaire, reporting physician diagnosis of asthma and allergic rhinitis, and use of asthma medication. Physical activity (PA) was measured using the short 7 days International Physical Activity Questionnaire (IPAQ) (8). A combined total physical activity was computed as the sum of the activity domains scores (total PA = walking + moderate-intensity PA + vigorous-intensity PA) and reported as a continuous measure (total PA score = total MET-min/wk). Eosinophilic airway inflammation was assessed measuring lower airway’s exhaled nitric oxide (NO) levels according to guidelines, before a training session, using NIOX MINO (Aerocrine AB, Solna, Sweden), and expressed in parts per billion (p.p.b.). Atopy was defined by positive skin prick testing to common aeroallergens (Laboratorios LETI S.L., Spain). The study was performed at the swimming pool in which swimmers trained, except for the follow-up visit of past swimmers which occurred at the laboratory. Results were expressed as mean (SD) or, if not normally distributed, as median (interquartile range). Levels of exhaled NO and of physical activity were log-transformed because of skewed distribution. Differences between groups were assessed with one-way ANOVA or Kruskal–Wallis for normally or nonnormally distributed data or chi-Square for categorical variables. Differences in changes in exhaled NO after the 3-yr follow-up were assessed by general linear model adjusting on confounding factors: gender, age, atopy, physician-diagnosed asthma, and use of asthma medication. We observed a significant difference in changes in exhaled NO; those who remained active significantly increased their levels of eosinophilic airway inflammation independently of their gender, age, atopy, or asthma status (Table 2, Fig. 1). After the 3-yr follow-up, the prevalence of asthma, allergic rhinitis, and use of asthma medication increased significantly in both groups. All subjects increased their overall physical activity levels; however, significant increases in moderate and vigorous physical activity level were only observed in active swimmers.