Domain-Specific Physical Activity And Sedentary Behaviour In Relation To Colorectal Cancer Risk: A Systematic Review And Meta-Analysis

Mahmood SHAHID, The University of Melbourne, Australia
ROBERT M. 1,2 , DALLAS E. 1,2 , AMALIA K. 1 , BRIGID L. 1,2

1 Melbourne School of Population and Global Health, The University of Melbourne, Melbourne, Australia
2 Cancer Epidemiology Centre, Cancer Council Victoria, Melbourne, Australia

Purpose:  Physical activity reduces colorectal cancer risk; however, most studies addressing this research question have focused on physical activity performed within the occupation or recreation domains.  The evidence in regards to other domains of physical activity and sedentary behaviour is limited and inconsistent. The purpose of this review was to examine associations of domain-specific physical activity and sedentary behaviour with colorectal cancer risk.  
Methods:  Medline, EMBASE and Web of Science were systematically searched from inception to December 2015 for cohort and case-control studies addressing this topic.  Data from 17 cohort and 21 case-control studies were extracted, and pooled estimates were computed using random-effects meta-analysis. Meta-regression analyses were conducted to investigate whether the risk estimates differ by sex, cancer sub-site and study design.
Results:  Comparing the highest versus lowest levels of domain-specific physical activity, the risk of colon cancer was 20% lower in individuals who were most active in the occupation (RR=0.80, 95%CI:0.67-0.96) and recreation (RR=0.80, 95%CI:0.72-0.89) domains, whereas weak or no associations were observed for rectal cancer (occupation RR=0.94, 95%CI:0.80-1.10; recreation RR=0.87, 95%CI:0.75-1.01).  We noted non-significant colon cancer risk reductions for physical activity within the transport (RR=0.59, 95%CI:0.32-1.09) and household (RR=0.86, 95%CI:0.70-1.04) domains, but virtually null associations for rectal cancer (P>0.5).  Sedentary behaviour was associated with increased colon cancer risk within the occupation domain (RR=1.44, 95%CI:1.29-1.62), but not with rectal cancer risk (RR=1.04, 95%CI:0.84-1.27).  We noted significant heterogeneity across the studies, with differences in estimates mainly due to sex and cancer sub-site.  
Conclusions:  There is consistent evidence that physical activity in occupation and recreation domains reduces colon cancer risk; additional studies are required to improve precision in estimates for other domains.  Reducing sedentary behaviour in the workplace may be an additional strategy to reduce colon cancer risk.
Funding source:   Melbourne International Research Scholarship, awarded to Dr Mahmood.