Positive Association Between Diabetes Mellitus and Risk of Colorectal Cancer

Introduction: In recent years, many studies employed and found an association between type 2 diabetes mellitus and colorectal cancer. Although increased risk of colorectal cancer in individuals with Non Insulin Dependent Diabetes Mellitus (NIDDM) has been observed in previous studies, limited information is available on the colorectal cancer associated with NIDDM in Iran. The purpose of this study was to define colorectal cancer risk associated with diabetes mellitus. Material & Methods: The present study was designed as an unmatched case control study. Cases were 393 patients with histologically confirmed colorectal carcinomas and 393 controls were randomly selected among the healthy participants in a health survey. To control potential confounding factors such as sex, age, smoking habits and Body Mass Index (BMI), multiple logistic regression model was fitted to obtain Odds Ratio of colorectal cancer and the corresponding 95% CIs, according to history of diabetes mellitus. Results: Overall, 86 (10%) cases versus 15 (1.7%) controls gave a history of diabetes mellitus. The corresponding multivariate OR was 6.77 (CI 95%: 3.84-11.92) indicating that having a positive history of diabetes mellitus increases one's risk of colorectal cancer about six-fold. The risk of colorectal cancer was slightly increased for women (p<0.05). Current smokers were at a higher CRC risk (OR=2.83, CI95%: 2.13-3.76) than never smokers. Conclusion: We found a strong positive association between NIDDM and prevalent colorectal cancer. In summary, these findings provide further indirect epidemiological evidence for the hypothesis that hyperinsulinaemia may be important in the development of colorectal cancer.