Article Text

  1. D. Garrow,
  2. L. Egede
  1. Medical University of South Carolina, Charleston, SC


Objectives To determine the prevalence of colorectal cancer among individuals with and without diabetes in a large nationally representative survey. To ascertain if there are increased odds of having colorectal cancer among individuals with diabetes mellitus after controlling for relevant confounders.

Background Colorectal cancer is the third most common type of cancer and second most common cause of cancer-related death in the United States. An emerging risk factor for colorectal cancer is type 2 diabetes mellitus. Biochemical mechanisms postulated for this risk include hyperinsulinemia and elevated serum C-peptide levels, both of which affect colon mucosa adversely in vitro.

Methods Data source: National Health Interview Survey (NHIS) 1997-2003, conducted by the National Center for Health Statistics. The NHIS is a comprehensive nationally representative survey weighted to represent the US adult population. Subjects selected by a complex sampling design involving stratification, clustering, and multistage sampling with a nonzero probability of selection for each person. There were 226,953 subjects represented in the combined 7 years of the NHIS, of which 13,399 reported a history of diabetes (5.9%). Dependent variable was colorectal cancer history, defined by an affirmative answer to "Have you ever been told by a health care professional that you have colon or rectal cancer? " The primary independent variable was a reported history of diabetes. Relevant covariates included age, race, gender, smoking history, alcohol use, and obesity. NHIS data from 1997-2003 were merged with SAS v. 9.1.3. Analyses performed with STATA v. 8.0, which accounted for the complex survey design of the NHIS and generated population estimates. Multiple logistic regression was used to determine whether diabetes was independently associated with colorectal cancer.

Results Individuals with diabetes were more likely to have a history of colorectal cancer than individuals without diabetes (1.34% vs 0.47%, p < .001). After controlling for relevant confounders, the odds of having a history of colorectal cancer among individuals with diabetes was 1.4 times the odds of colorectal cancer among people without diabetes (CIs = 1.15 to 1.67).

Conclusions The prevalence of colorectal cancer is nearly 3 times as high among individuals with diabetes as compared to subjects without diabetes. After controlling for relevant confounders, the odds of having colorectal cancer were significantly higher among people with diabetes. People age 50 and older, Caucasians, and former smokers were all more likely to have a history of colorectal cancer. If this association remains positive in prospective trials, people with diabetes may require more aggressive screening for colorectal cancer than the general population. Research should be directed at understanding the pathophysiologic reasons why diabetes is associated with colorectal cancer.

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