Background: Physical activity may protect against bladder cancer through several biologic pathways, such as enhanced immune function and decreased chronic inflammation. Physical activity may also indirectly prevent bladder cancer by reducing obesity. A sizeable number of epidemiologic studies have examined the association between physical activity and bladder cancer, but the available evidence has not yet been formally summarised using meta-analysis.
Methods: We performed a systematic literature review and meta-analysis of English-language studies published from January 1975 through November 2013. We followed the PRISMA guidelines and used a random effects model to estimate the summary risk estimates for the association between physical activity and bladder cancer.
Results: A total of 15 studies with 5,402,369 subjects and 27,784 bladder cancer cases were included. High vs low levels of physical activity were related to decreased bladder cancer risk (summary relative risk (RR)=0.85, 95% confidence interval (CI)=0.74-0.98; I(2)=83%; P-value for heterogeneity across all studies<0.001). Results were similar for cohort studies (RR=0.89, 95% CI=0.80-1.00; I(2)=64%) and case-control studies (RR=0.71, 95% CI=0.43-1.16; I(2)=87%; P-value for difference=0.108) and they were comparable for women (RR=0.83, 95% CI=0.73-0.94; I(2)=0%) and men (RR=0.92, 95% CI=0.82-1.05; I(2)=67; P-value for difference=0.657). Findings were also comparable for recreational (RR=0.81, 95% CI=0.66-0.99; I(2)=77%) and occupational physical activity (RR=0.90, 95% CI=0.76-1.0; I(2)=76%; P-value for difference=0.374), and they were largely consistent for moderate (RR=0.85, 95% CI=0.75-0.98; I(2)=76%) and vigorous activity (RR=0.80, 95% CI=0.64-1.00;I(2)=87%; P-value for difference=0.535).
Conclusions: Physical activity is associated with decreased risk of bladder cancer. Further studies are required to assess the relations of intensity, frequency, duration, and timing in life of physical activity to bladder cancer risk.