title: Physical activity and asthma: a systematic review and meta-analysis.
abstract: BACKGROUND
  This review aims to give an overview of available published evidence concerning the association between physical activity and asthma in children, adolescents and adults.
  
  
  METHODS
  We included all original articles in which both physical activity and asthma were assessed in case-control, cross-sectional or longitudinal (cohort) studies. Excluded were studies concerning physical fitness, studies in athletes, therapeutic or rehabilitation intervention studies such as physical training or exercise in asthma patients. Methodological quality of the included articles was assessed according to the Newcastle-Ottawa Scale (NOS).
  
  
  RESULTS
  A literature search was performed until June 2011 and resulted in 6,951 publications derived from PubMed and 1,978 publications from EMBASE. In total, 39 studies met the inclusion criteria: 5 longitudinal studies (total number of subjects n = 85,117) with physical activity at baseline as exposure, and asthma incidence as outcome. Thirty-four cross-sectional studies (n = 661,222) were included. Pooling of the longitudinal studies showed that subjects with higher physical activity levels had lower incidence of asthma (odds ratio 0.88 (95% CI: 0.77-1.01)). When restricting pooling to the 4 prospective studies with moderate to good study quality (defined as NOS≥5) the pooled odds ratio only changed slightly (0.87 (95% CI: 0.77-0.99)). In the cross-sectional studies, due to large clinical variability and heterogeneity, further statistical analysis was not possible.
  
  
  CONCLUSIONS
  The available evidence indicates that physical activity is a possible protective factor against asthma development. The heterogeneity suggests that possible relevant effects remain hidden in critical age periods, sex differences, or extremes of levels of physical activity (e.g. sedentary). Future longitudinal studies should address these issues.
authors.affiliation: Department of Pediatrics, Radboud University Medical Centre, Nijmegen, The Netherlands. m.eijkemans@cukz.umcn.nl
authors.forename: Marianne
authors.initials: M
authors.lastname: Eijkemans
authors.forename: Monique
authors.initials: M
authors.lastname: Mommers
authors.forename: Jos M Th
authors.initials: JM
authors.lastname: Draaisma
authors.forename: Carel
authors.initials: C
authors.lastname: Thijs
authors.forename: Martin H
authors.initials: MH
authors.lastname: Prins
mesh_terms: D001249:Asthma / Q000453:epidemiology / Q000503:physiopathology*; D003430:Cross-Sectional Studies; D006801:Humans; D008137:Longitudinal Studies; D009043:Motor Activity