title: Physical activity and risk of gastric cancer: a meta-analysis of observational studies.
abstract: BACKGROUND
  Studies evaluating the relationship of physical activity and stomach cancer risk have yielded inconsistent and largely inconclusive results. We therefore conducted a systematic review and meta-analysis of observational studies that assessed the relationship between physical activity and risk of gastric cancer.
  
  
  METHODS
  Following a standard protocol, we searched medical literature databases (PubMed, EMBASE, CINAHL, PsycINFO and Google Scholar) from inception to July 2012, and conducted a random effects meta-analysis.
  
  
  RESULTS
  Seven prospective cohorts and four case-control studies of physical activity and gastric cancer risk, with 1,535,006 people and 7944 cases of gastric cancer were included. We found a modest protective association between sufficient physical activity and gastric cancer risk (relative risk: 0.81 (95% CI 0.69 to 0.96); I(2)=68.5%) in the prospective studies and (relative risk: 0.78 (95% CI 0.66 to 0.91); I(2)=0%) in case-control studies. The association appeared weaker in smokers than in non-smokers (p heterogeneity=0.035). The association may also be weaker for gastric cardia cancer relative to the distal non-cardia subtypes. Physical activity type (recreational or occupational), intake of alcohol, total energy intake, consumption of fruits and vegetables and infection with Helicobacter pylori had no influence on the association. The effect measure from cohort studies (relative risk: 0.82 (95% CI 0.70 to 0.97); I(2)=61.7%) and case-control studies (relative risk: 0.83 (95% CI 0.66 to 1.04); I(2)=49.8%) did not differ materially at higher physical activity levels.
  
  
  CONCLUSIONS
  We conclude that a regular physical activity may be protective against stomach cancer risk.
authors.affiliation: Department of Global Health and Population, Harvard School of Public Health, Boston, Massachusetts, USA.
authors.forename: Ajibola Ibraheem
authors.initials: AI
authors.lastname: Abioye
authors.affiliation: Newgate Medical Services Limited, Ikorodu, Lagos, Nigeria.
authors.forename: Majeed Olaniyi
authors.initials: MO
authors.lastname: Odesanya
authors.affiliation: Community Health Unit, Lagos State General Hospital, Igando, Lagos, Nigeria.
authors.forename: Asanat Iyabode
authors.initials: AI
authors.lastname: Abioye
authors.affiliation: Department of Surgery, Lagos State University College of Medicine, Ikeja, Lagos, Nigeria.
authors.forename: Nasiru Akanmu
authors.initials: NA
authors.lastname: Ibrahim
mesh_terms: D002299:Cardia; D016021:Epidemiologic Studies; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D064887:Observational Studies as Topic; D017594:Publication Bias; D012307:Risk Factors; D012737:Sex Factors; D012907:Smoking / Q000009:adverse effects; D013274:Stomach Neoplasms / Q000517:prevention & control*
keywords: Epidemiology; Evidence based reviews; Exercise; Health promotion through physical activity