Diabetes mellitus and the incidence and mortality of colorectal cancer: a meta‐analysis of 24 cohort studies

Aim The incidence and mortality of colorectal cancer (CRC) were quantified in persons with and without diabetes mellitus (DM). Method Medline and Embase were searched for articles published before July 2010. Cohort studies that evaluated incidence and mortality of DM and CRC were included. The initial search identified 1887 titles, of which 24 articles met the inclusion criteria. We defined the relative risk (RR) as the metric of choice; 95% confidence intervals (CIs) were calculated with a random‐effects model. Results There was an increase in the RR of developing CRC in persons with DM compared with those without DM (RR 1.28; 95% CI 1.19–1.39), without heterogeneity between studies (P_{heterogeneity} = 0.13). The association between duration of DM and CRC incidence was stronger in the 11–15‐year group (RR 1.51; 95% CI 1.12–2.03) than in the <10‐year group (RR 1.05; 95% CI 0.90–1.22) and the >15‐year group (RR 1.25; 95% CI 0.80–1.94), and there was significant heterogeneity among subgroups (P_{heterogeneity} = 0.01). In studies reporting standardized incidence ratios (SIRs), there was an increased incidence of CRC with DM (RR 1.27; 95% CI 1.14–1.42; P_{heterogeneity} = 0.09), and the association was stronger among men (RR 1.47; 95% CI 1.15–1.86) than women (RR 1.08; 95% CI 1.00–1.17); there was significant heterogeneity among gender (P_{heterogeneity} = 0.01). Conclusion This meta‐analysis suggests that individuals with DM have a significant increase in risk of developing CRC.