Abdominal obesity and the risk of colorectal adenoma: a meta-analysis of observational studies

Inconsistent results regarding the association between abdominal obesity and the risk of colorectal adenoma (CRA), the precursor of colorectal cancer (CRC), have been reported. To provide a quantitative assessment of this relationship, we summarized the evidence from observational studies in categorical, linear dose-response meta-analyses. We searched MEDLINE and EMBASE for studies of waist circumference (WC) and/or waist-hip ratio (WHR) and CRA risk published until the end of October 2011. Summary relative risks (SRRs) with 95% confidence intervals (CIs) were summarized using a random-effects model. Between-study heterogeneity was assessed using the Cochran's Q and I-2 statistics. A total of 21 studies (four case-control studies, 12 cross-sectional studies, and five cohort studies) were included in this meta-analysis. Overall, the SRRs of CRA were 1.39 (95% CI: 1.24-1.56) for the highest versus the lowest level of WC and 1.22 (95% CI: 1.10-1.35) for WHR (P-value for heterogeneity 0.013 and 0.458, respectively). In linear dose-response analysis, a 10-cm increase in WC was related to an increased risk of CRA (SRR, 1.19; 95% CI, 1.13-1.26) and a 0.1-unit increment in WHR gave 1.16 (95% CI: 1.06-1.26). Subgroup analyses revealed that the increased risk of CRA in abdominally obese individuals was independent of geographic location, design, sex, and confounders: alcohol use, smoking status, and family history of colorectal cancer. However, BMI may be a confounder for the association between WC and CRA risk. These results suggest that abdominally obese individuals, both men and women, may have an increased risk of CRA. European Journal of Cancer Prevention 21: 523-531 (C) 2012 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.