High training volume is associated with increased prevalence of non-allergic asthma in competitive cross-country skiers

Background Cross-country skiers have a high prevalence of asthma, but its phenotypes and association with success in competitions are not known. Objective To investigate, by means of a postal survey, the relative proportions of allergic and non-allergic asthma in competitive cross-country skiers compared with the general population, to study how performance level and training volume are related to asthma and its type and to assess the possible risk factors for allergic and non-allergic asthma in competitive skiers. Methods All Finnish cross-country skiers enrolled in the largest national competitions in winter 2019 (n=1282), and a random sample (n=1754) of the general population of the same age were sent a postal questionnaire. The response rate was 27.4% (n=351) for skiers and 19.5% (n=338) for the controls. International Ski Federation (FIS) ranking points measured the level of success in skiers. Asthma was defined as self-reported, physician-diagnosed asthma. Asthma was considered allergic if associated with doctor-diagnosed allergy, and exposure to allergens provoked asthma symptoms. Results The prevalence of asthma was higher in skiers than in the controls (25.9% vs 9.2%, p<0.001), and it was the highest (56.1%) in the most successful quartile of skiers. Asthma was more often non-allergic in skiers than in the controls (60.1% vs 38.7%, p=0.036). Being a skier came with a higher risk for non-allergic (OR 5.05, 95% CI 2.65 to 9.61) than allergic asthma (OR 1.92, 1.08-3.42). Using multivariable regression analysis, training volume was associated with non-allergic asthma, while age, family history of asthma and allergic rhinitis were associated with allergic asthma. Conclusion The prevalence of asthma is the highest in the most successful cross-country skiers. The asthma in skiers is mostly non-allergic compared with the general population of the same age. The most important risk factor for non-allergic asthma in skiers is high training volume.