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 We included 19 reviews covering 22 cancer sites, 26 exposure-outcome pairs meta-analyses and 541 original studies. Physical activity was associated with lower risk of seven cancer sites (colon, breast, endometrial, lung, oesophageal, pancreas and meningioma). Only colon (a protective association with recreational physical activity) and breast cancer (a protective association with overall physical activity) were supported by strong evidence and highly suggestive evidence, respectively. Evidence from endometrial, lung, oesophageal, pancreas and meningioma presented hints of uncertainty and bias in the literature (eg, not reaching P values<10-6) 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.
- physical activity
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Contributors All authors conceived and designed the study. LFMR, JPRL and THS acquired and collated the data. LFMR and GM analysed the data. All authors drafted and critically revised the manuscript for important intellectual content and gave final approval of the version to be published.
Funding This work was supported by São Paulo Research Foundation (FAPESP), grant#2014/25614-4 (funding was obtained from FAPESP as part of LFMR doctoral scholarship); World Cancer Research Fund International Regular Grant Programme (2014/1180 to KKT; funding was obtained from World Cancer Research Fund (WCRF UK), as part of the World Cancer Research Fund International grant programme). JPRL is postdoctoral fellowship from the University of Sydney (Australia) (Project Code: U2334).
Competing interests None declared.
Provenance and peer review Commissioned; externally peer reviewed.
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