Metabolic risk factors of colorectal cancer: Umbrella review

Background and aim: The association between metabolic factors and colorectal cancer (CRC) risk is inconclusive. This umbrella review aimed to summarise and describe the association using existing systematic reviews and/or meta-analyses. Method: Four databases (Medline, Scopus, Web of Science, and Cochrane Library) were searched for systematic reviews and/or meta-analyses of observational studies. Two independent authors extracted data on the summary estimated effect and heterogeneity of studies using I² from the individual reviews. The Assessing the Methodological Quality of Systematic Reviews (AMSTAR 2) tool was used to evaluate the methodological quality. Results: 49 articles were included in this review. Although most included studies were graded with critically low methodological quality (81.6 %), we found a significant positive association between obesity (summary relative risk (SRR) range 1.19–1.49), diabetes mellitus (SRR range 1.20–1.37), hypertension (SRR range 1.07–1.62), metabolic syndrome (SRR range 1.25–1.36), non-alcoholic fatty liver disease (pooled odds ratio (POR) range 1.13–1.56), and risk of CRC. Higher serum high-density lipoprotein cholesterol levels were associated with a lower risk of CRC in 3/6 reviews, while others did not find any association. There was no clear association between high triglyceride levels, total cholesterol levels, low-density lipoprotein cholesterol levels, and risk of CRC. Conclusion: This umbrella review identified that most metabolic factors are significantly associated with increased risk of CRC. Thus, people affected by metabolic factors may be benefited from CRC screening and surveillance.