Lifestyle factors and colorectal cancer risk (1): systematic review and meta-analysis of associations with body mass index


Dr Andrew Renehan, Department of Surgery, University of Manchester, The Christie NHS Foundation Trust, Wilmslow Road, Manchester M20 4BX UK.


Objective  Excess body weight, defined by body mass index (BMI), may increase the risk of colorectal cancer. As a prerequisite to the determination of lifestyle attributable risks, we undertook a systematic review and meta-analysis of prospective observational studies to quantify colorectal cancer risk associated with increased BMI and explore for differences by gender, sub-site and study characteristics.

Method  We searched MEDLINE and EMBASE (to December 2007), and other sources, selecting reports based on strict inclusion criteria. Random-effects meta-analyses and meta-regressions of study-specific incremental estimates were performed to determine the risk ratio (RR) and 95% confidence intervals (CIs) associated with a 5 kg/m2 increase in BMI.

Results  We analysed 29 datasets from 28 articles, including 67 361 incident cases. Higher BMI was associated with colon (RR 1.24, 95% CIs: 1.20–1.28) and rectal (1.09, 1.05–1.14) cancers in men, and with colon cancer (1.09, 1.04–1.12) in women. Associations were stronger in men than in women for colon (P < 0.001) and rectal (P = 0.005) cancers. Associations were generally consistent across geographic populations. Study characteristics and adjustments accounted for only moderate variations of associations.

Conclusion  Increasing BMI is associated with a modest increased risk of developing colon and rectal cancers, but this modest risk may translate to large attributable proportions in high-prevalence obese populations. Inter-gender differences point to potentially important mechanistic differences, which merit further research.