title: Does exercise increase the risk of upper respiratory tract infections?
abstract: BACKGROUND
  Heavy exercise induces marked immunodepression, which is multifactorial in origin. Evidence showing clinical significance of this immunodepression is scarce.
  
  
  METHODS
  We assessed in a systematic manner whether physical activity or intensity of exercise increase susceptibility to upper respiratory tract infections (URTI). A literature search was performed using the keywords 'upper respiratory tract infections', 'athletes', 'exercise' and 'physical activity'. We considered all studies reporting of the effect of exercise, physical activity, sport and training on susceptibility to URTI. A total of 162 publications were identified and 30 studies were eligible (4 descriptive, 18 observational and 8 interventional). The 30 studies included 8595 athletes (5471 runners, 2803 swimmers) and 1798 non-athletes.
  
  
  RESULTS
  Moderate activity may enhance immune function, whereas prolonged, high-intensity exercise temporarily impairs the immune competence. Athletes, when compared with lesser active individuals, experience higher rate of URTI after training and competitions. In non-athletes, increasing physical activity is associated with a decreased risk of URTI.
  
  
  RESULTS
  The relationship between exercise and URTI is affected by poorly known individual determinants such as genetic factors, fitness, nutritional status or atopy. Elite athletes may have a decreased susceptibility to URTI.
  
  
  CONCLUSIONS
  The dose-response relationship between immunodepression and risk for URTI during the weeks following heavy exercise. What are the clinically relevant methods to assess exercise-induced immunodepression? Is down-regulation of immunity after intense exercise a protective response to limit inflammation? Is there a role for nutritional or pharmaceutical interventions to reduce risk of URTI?
authors.affiliation: Department of Immunology, Faculty of Medicine, University of Porto, Al. Prof. Hernâni Monteiro, 4202 Porto, Portugal. andremoreira@med.up.pt
authors.forename: André
authors.initials: A
authors.lastname: Moreira
authors.forename: Luís
authors.initials: L
authors.lastname: Delgado
authors.forename: Pedro
authors.initials: P
authors.lastname: Moreira
authors.forename: Tari
authors.initials: T
authors.lastname: Haahtela