Asthma is defined as a chronic airway inflammatory disease, whose pathogenesis involves a variety of cells and inflammatory mediators, partly conditioned by genetic factors, resulting in bronchial hyperresponsiveness and variable airflow obstruction, with recurrent episodes of wheezing, dyspnoea, chest tightness and coughing. This type of disease is most frequently seen in athletes, who are more susceptible to it than the general population due to the inherent high demands of elite training.

Asthma in athletes consists of at least two different clinical endotypes: early-onset and late-onset, the latter being highly likely to be exercise-induced. The disease has a higher prevalence in athletes involved in endurance sports, and while the exact reason for this pattern is still unknown, the answer possibly lies in prolonged exposure to mechanical stress on the airway epithelium during increased ventilation, leading to chronic airway damage.

Types of asthma according to endotypes

The search for endotypes of asthma in elite athletes has led to a simplified categorisation of asthma into Type 2 and Non-Type 2 inflammatory disease.

Type 2 Asthma

Type 2 asthma can present two variants. The most frequent one is allergic asthma, which accounts for 40-50% of severe asthma and has an atopic mechanism. Diagnosis requires the demonstration of sensitisation to an allergen and the triggering of symptoms linked to exposure to the allergen.

Eosinophilic asthma, on the other hand, accounts for 25% of severe asthma and is characterised by eosinophilic inflammation. It may be associated with chronic rhinosinusitis and polyposis.

Non-Type 2 asthma

Non-Type 2 asthma usually does not include peripheral eosinophilia or the presence of sputum. It usually occurs in patients with a smoking history and may be accompanied by chronic airflow obstruction.

Study on asthma in athletes

A study on asthma endotypes led by Soren Malte Rasmussen (Asthma endotypes in elite athletes: A cross-sectional study of European athletes participating in the Olympic Games)^[1] took a sample of 1375 elite athletes who were subjected to the Allergy Questionnaire for Athletes (AQUA) prior to the Beijing 2008 Olympic Games. The athletic disciplines were divided into two categories: endurance and non-endurance. Athletes were classified according to whether they had been previously diagnosed with asthma before, had respiratory symptoms, a positive bronchial challenge test to methacholine, mannitol, or voluntary eucapnic hyperventilation.

The study found that 16.5% of the participants had asthma. Asthma was more prevalent in athletes involved in endurance sports, while Type 2 asthma (90 athletes; 69.8% of the total) was more prevalent than Non-Type 2 asthma (39 athletes; 30.4% of the total).

Athletes with Type 2 asthma generally had symptoms consistent with allergic rhinitis and conjunctivitis, whereas athletes with Non-Type 2 asthma had significantly fewer allergic symptoms and fewer diagnoses of rhinitis. These findings suggest that Non-Type 2 asthma may develop among athletes after several years of intensive training.

Moreover, the study suggests that asthma among endurance athletes may arise due to prolonged mechanical stress of the airway surface and increased ventilation resulting in airway remodelling. This could indicate that there is a specific underlying pathogenic mechanism, mostly related to endurance sports.

Conclusions of the study on sport-induced asthma

The study showed a higher prevalence of asthma among elite athletes, with the highest prevalence among those involved in endurance sports. The most frequent endotype was Type-2 asthma, although 30% of the athletes had Non-Type-2 asthma, a higher than expected result considering that this was a young population group. Therefore, these results suggest that there are indicators that asthma may develop in relation to training.

^[1] Rasmussen SM, Halvard Hansen ES, Stensrud T, Radon K, Wolfarth B, Kurowski M, Bousquet J, Bonini S, Bonini M, Delgado L, Moreira A, Drobnic F, Papadopoulos NG, Vakali S, Gratziou C, Malmberg LP, Haahtela T, Backer V. Asthma endotypes in elite athletes: A cross-sectional study of European athletes participating in the Olympic Games. Allergy. 2022 Jul;77(7):2250-2253. doi: 10.1111/all.15313. Epub 2022 May 5. PMID: 35426975.