Diabetes Mellitus and Risk of Colorectal Cancer: A Meta-Analysis

Susanna C. Larsson, Nicola Orsini, Alicja Wolk
2005 Journal of the National Cancer Institute  
Diabetes has been associated with an increased risk of colorectal cancer in most, but not all, studies. Findings have also been inconclusive with regard to sex and subsite in the colorectum. To resolve these inconsistencies, we conducted a meta-analysis of published data on the association between diabetes and the incidence and mortality of colorectal cancer. Methods: We identifi ed studies by a literature search of Medline from January 1, 1966, through July 31, 2005, and by searching the
more » ... nce lists of pertinent articles. Summary relative risks (RRs) with 95% confi dence intervals (CIs) were calculated with a random-effects model. All statistical tests were two-sided. Results: Analysis of 15 studies (six case -control and nine cohort studies), including 2 593 935 participants, found that diabetes was associated with an increased risk of colorectal cancer, compared with no diabetes (summary RR of colorectal cancer incidence = 1.30, 95% CI = 1.20 to 1.40), without heterogeneity between studies ( P heterogeneity = .21). These results were consistent between case -control and cohort studies and between studies conducted in the United States and in Europe. The association between diabetes and colorectal cancer incidence did not differ statistically signifi cantly by sex (summary RR among women = 1.33, 95% CI = 1.23 to 1.44; summary RR among men = 1.29, 95% CI = 1.15 to 1.44; P heterogeneity = .26) or by cancer subsite (summary RR for colon = 1.43, 95% CI = 1.28 to 1.60; summary RR for rectum = 1.33, 95% CI = 1.14 to 1.54; P heterogeneity = .42). Diabetes was positively associated with colorectal cancer mortality (summary RR = 1.26, 95% CI = 1.05 to 1.50), but there was evidence for heterogeneity between studies ( P heterogeneity = .04). Conclusions: Our fi ndings strongly support a relationship between diabetes and increased risk of colon and rectal cancer in both women and men. [J Natl Cancer Inst 2005;97:1679 -87] Type 2 diabetes mellitus and colorectal cancer are major causes of morbidity and mortality in the United States and other Western countries ( 1 -3 ) . Dietary and lifestyle risk factors for developing insulin resistance and type 2 diabetes, such as Western diet, physical inactivity, and obesity, have also been linked to an increased risk of colon cancer ( 4 -7 ) . On the basis of the overlapping risk factors, it has been hypothesized that diabetes itself may be a risk factor for colon cancer ( 8 ) . Although epidemiologic studies of the relationship of diabetes with the risk of colorectal cancer are not entirely consistent, most studies are compatible with a positive association. In some studies, the association appeared to be stronger for colon cancer than for rectal cancer ( 9 -12 ) , or the association was observed only in
doi:10.1093/jnci/dji375 pmid:16288121 fatcat:smzdwoophzgwvpai6jkmmats34