High concentrations of nitrogen dioxide in London could increase breathing problems among Olympic athletes, according to a leading sports medicine committee.

According to Dr. William S. Silvers of the American Academy of Allergy, Asthma & Immunology (AAAAI), the air quality in London during the 2012 Olympic games — set to start in three days — could cause a “narrowing of the airways” in athletes competing outdoors.

Currently, London has a higher concentration of nitrogen dioxide in the atmosphere than Beijing, China, had during the last summer Olympic games before the Chinese government banned half of all cars in an effort to reduce pollution. London has spent far less than China did to address air pollution.

The AAAAI concludes:

According to the American Academy of Allergy, Asthma & Immunology, [exercise-induced bronchoconstriction or EIB] affects an estimated 20% of top athletes and an estimated 1 in 6 of all Olympic athletes.

“It has been well documented that elite athletes in the Olympics have an increased prevalence of EIB. They may not have suspected it, since they don’t have chronic asthma but rather a narrowing of the airways that comes specifically with exercise,” explained William S. Silvers, MD, FAAAAI, of the AAAAI’s Sports Medicine Committee.

An added concern for athletes with asthma and EIB is the amount of pollution in London, which may cause symptoms to worsen. Ozone, sulfur dioxide, nitric oxide and other pollutants can inflame the airways of sensitive people and even cause an asthma attack.

Asthma attacks and incidences of EIB could have serious impacts on the athletes’ health and performance at the Games. The UK is not in compliance with European Union air quality guidelines and the organization Clean Air in London is concerned that the pollution might be a problem for spectators of the games as well.

In response to concerns expressed by advocacy groups and public health officials, the London Air Quality Network has set up a website, londonair.org.uk, to provide up-to-date information on air quality at Olympic venues around the city.