Recent studies proved that patients with diabetes were at significantly higher risk of developing colorectal cancer. However, the association between diabetes mellitus and the risk of colorectal adenoma remains undefined. Thus we conducted an updated meta-analysis to identify the association between diabetes mellitus and the risk of colorectal neoplasia including adenoma and cancer.

We conducted a search in databases including Pubmed, Web of Science, EMBASE Databases, Cochrane CENTRAL, Wanfang Data, and CNKI database. Case-control and cohort studies were included. All articles were published before January 2015 and the quality of each study was evaluated by the Newcastle-Ottawa Scale. Odds ratios (ORs) or relative risks (RRs) and its corresponding 95% confidence intervals (CIs) for each study were calculated and summary relative risk estimates with corresponding 95% CIs were generated using the random-effects model. Heterogeneity and publication bias were assessed.

Twenty-nine articles including ten case-control studies and nineteen cohort studies were included in this meta-analysis. In a pooled analysis of all studies, diabetes mellitus was associated with increased risk of colorectal neoplasia (RR=1.35, 95% CI=1.28–1.42). The risk increased significantly for both colorectal cancer (RR=1.37, 95% CI=1.30–1.45) and adenoma (RR=1.26, 95% CI=1.11–1.44). Subgroup analyses on study design, gender, geographical region, and type of diabetes mellitus further evidenced these findings.

Diabetes mellitus was associated with an increased risk of colorectal neoplasia. Not only the increased risk of colorectal cancer but also the higher risk of adenoma was identified in patients with diabetes mellitus.