Diabetes mellitus and risk of colorectal cancer: a meta-analysis.
BACKGROUND
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 identified studies by a literature search of Medline from January 1, 1966, through July 31, 2005, and by searching the reference lists of pertinent articles. Summary relative risks (RRs) with 95% confidence 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 significantly 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 findings strongly support a relationship between diabetes and increased risk of colon and rectal cancer in both women and men.
Larsson
Susanna C
SC
Division of Nutritional Epidemiology, The National Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden . susanna.larsson@ki.se
Orsini
Nicola
N
Wolk
Alicja
A
D016022:Case-Control Studies; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000453:epidemiology* / Q000209:etiology* / Q000401:mortality; D016001:Confidence Intervals; D048909:Diabetes Complications / Q000453:epidemiology*; D003924:Diabetes Mellitus, Type 2 / Q000150:complications*; D005060:Europe / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D018570:Risk Assessment; D014481:United States / Q000453:epidemiology