title: Leisure-time physical activity and lung cancer risk: A systematic review and meta-analysis.
abstract: OBJECTIVE
  We conducted a systematic review and meta-analysis of the association between recreational physical activity and lung cancer risk to update previous analyses and to examine population subgroups of interest defined by smoking status and histology.
  
  
  METHODS
  We searched the PubMed database for studies up to May 2015. Individual study characteristics were abstracted including study design, number of cases, assessment of recreational physical activity and type and level of adjustment for confounding factors. Combined effect estimates were calculated for the overall associations and across subgroups of interest.
  
  
  RESULTS
  We identified 28 studies that were eligible for inclusion in the meta-analysis. The overall analysis indicated an inverse association between recreational physical activity and lung cancer risk (Relative Risk (RR), 0.76; 95% Confidence Interval (CI), 0.69-0.85, p-value: <0.001). Similar inverse associations with risk were also noted for all evaluated histological subtypes, including adenocarcinoma (RR, 0.80; 95% CI, 0.72-0.88), squamous (RR, 0.80; 95% CI, 0.71-0.90) and small cell (RR, 0.79; 95% CI, 0.66-0.94). When we examined effects by smoking status, inverse associations between recreational physical activity and lung cancer risk were observed among former (RR, 0.77; 95% CI, 0.69-0.85) and current smokers (RR, 0.77; 95% CI, 0.72-0.83), but not among never smokers (RR, 0.96; 95% CI, 0.79-1.18).
  
  
  CONCLUSIONS
  Results from this meta-analysis suggest that regular recreational physical activity may be associated with reduced risk of lung cancer. Only four studies examining never smokers were identified, suggesting the need for additional research in this population.
authors.affiliation: Department of Cancer Epidemiology and Prevention Research, Cancer Control Alberta, Alberta Health Services, Canada; Department of Community Health Sciences, Cumming School of Medicine, University of Calgary, Canada; Department of Oncology, Cumming School of Medicine, University of Calgary, Canada. Electronic address: Darren.Brenner@albertahealthservices.ca.
authors.forename: Darren R
authors.initials: DR
authors.lastname: Brenner
authors.affiliation: Department of Cancer Epidemiology and Prevention Research, Cancer Control Alberta, Alberta Health Services, Canada; Department of Community Health Sciences, Cumming School of Medicine, University of Calgary, Canada.
authors.forename: Demetra H
authors.initials: DH
authors.lastname: Yannitsos
authors.affiliation: Department of Cancer Epidemiology and Prevention Research, Cancer Control Alberta, Alberta Health Services, Canada; Department of Community Health Sciences, Cumming School of Medicine, University of Calgary, Canada.
authors.forename: Megan S
authors.initials: MS
authors.lastname: Farris
authors.affiliation: Genetic Epidemiology Group, International Agency for Research on Cancer, Lyon, France.
authors.forename: Mattias
authors.initials: M
authors.lastname: Johansson
authors.affiliation: Department of Cancer Epidemiology and Prevention Research, Cancer Control Alberta, Alberta Health Services, Canada; Department of Community Health Sciences, Cumming School of Medicine, University of Calgary, Canada; Department of Oncology, Cumming School of Medicine, University of Calgary, Canada.
authors.forename: Christine M
authors.initials: CM
authors.lastname: Friedenreich
mesh_terms: D016022:Case-Control Studies; D015331:Cohort Studies; D006801:Humans; D007899:Leisure Activities; D008175:Lung Neoplasms / Q000453:epidemiology* / Q000209:etiology* / Q000473:pathology; D009043:Motor Activity; D016017:Odds Ratio; D012306:Risk; D012907:Smoking / Q000009:adverse effects