Circulating C-peptide level is a predictive factor for colorectal neoplasia: evidence from the meta-analysis of prospective studies

C-peptide, a hormone secreted by the pancreas, is a marker for insulin production and hyperinsulinemia. Epidemiological studies have suggested an association between circulating C-peptide level and colorectal neoplasia risk; however, the results were not always consistent. Herein, we conducted a systematic review and meta-analysis study to evaluate the association between circulating C-peptide level and the colorectal neoplasia risk. The PubMed database was searched for the eligibility studies updated to May 2013, which prospectively evaluated the association between circulating C-peptide level and colorectal neoplasia risk. The summary estimates and 95 % confidential intervals (95 % CIs) for those with the highest quantile C-peptide level in contrast to the lowest quantile were estimated with the random-effects model. Heterogeneity between the studies was assessed with the Q test and the I (2) statistic. Potential publication bias was evaluated with the Egger's test. We identified 9 nested case-control studies that have recruited a total of 3,109 cases and 4,285 controls met the criteria. From the meta-analysis, we found that subjects with high circulating C-peptide were associated with a 37 % increased colorectal neoplasia risk [pooled odds ratios (OR) 1.37, 95 % CI 1.09-1.72] under the random-effects model. In the stratification studies, we found the association was more prominent in the men (pooled OR 2.34, 95 % CI 1.36-4.04) compared to women (pooled OR 1.41, 95 % CI 0.89-2.25). Significant association between circulating C-peptide level and colon cancer risk was found (pooled OR 1.72, 95 % CI 1.26-2.36), but not for rectal cancer (pooled OR 1.14, 95 % CI 0.75-1.73). No significant publication bias was found for any meta-analysis study. In conclusion, the results of the meta-analysis studies suggested that higher circulating C-peptide could be a predictive factor for higher colorectal neoplasia susceptibility.