Colorectal cancer association with metabolic syndrome and its components: a systematic review with meta-analysis

We performed a systematic review and meta-analysis of the empirical evidence on the association of metabolic syndrome and its components with colorectal cancer incidence and mortality. A systematic literature search of multiple electronic databases was conducted and complemented by cross-referencing to identify studies published before 31 October 2012. Every included study was to report risk estimates with 95 % confidence intervals for the association between metabolic syndrome and colorectal cancer (incidence or mortality). Core items of identified studies were independently extracted by two reviewers, and results were summarized by standard methods of meta-analysis. We identified 17 studies, which reported on 49 data sets with 11,462 cancer cases. Metabolic syndrome was associated with an increased risk of colorectal cancer incidence and mortality in both men (RR: 1.33, 95 % CI 1.18-1.50, and 1.36, 1.25-1.48, respectively) and women (RR: 1.41, 1.18-1.70, and 1.16, 1.03-1.30, respectively). The risk estimates changed little depending on type of study (cohort vs non cohort), populations (US, Europe, Asia), cancer site (colon and rectum), or definition of the syndrome. The risk estimates for any single factor of the syndrome were significant for higher values of BMI/waist (RR: 1.19, 95 % CI 1.10-1.28), dysglycemia (RR: 1.29, 1.11-1.49), and higher blood pressure (RR: 1.09, 1.01-1.18). Dysglycemia and/or higher BMI/waist explained most of the risk associated with metabolic syndrome. Metabolic syndrome is associated with an increased risk of colorectal cancer incidence and mortality in both sexes. The risk conveyed by the full syndrome is not superior to the sum of its parts.