Physical activity and cancer: an umbrella review of the literature including 22 major anatomical sites and 770 000 cancer cases

OBJECTIVE: To provide an overview of the breadth and validity of claimed associations between physical activity and risk of developing or dying from cancer. DESIGN: Umbrella review. DATA SOURCES: We searched Medline, Embase, Cochrane Database and Web of Science. ELIGIBILITY CRITERIA FOR SELECTING STUDIES: Systematic reviews about physical activity and cancer incidence and cancer mortality in different body sites among general population. RESULTS: ) showing large between-study heterogeneity and/or not demonstrating a definite direction for the effect when 95% prediction intervals were considered. Four of the 26 meta-analyses showed small study effects and 4 showed excess significance. CONCLUSION: Physical activity is associated with a lower risk of several cancers, but only colon and breast cancer associations were supported by strong or highly suggestive evidence, respectively. Evidence from other cancer sites was less consistent, presenting hints of uncertainty and/or bias.