Diabetes and Sex-specific Colorectal Cancer Risks in Newfoundland and Labrador: A Population-based Retrospective Cohort Study

OBJECTIVE: Studies on the relationship between diabetes and colorectal cancer (CRC) are inconsistent. It is also unclear whether CRC risk elevation for individuals with diabetes is similar for males and females. Using data from Newfoundland and Labrador (NL), the province with the highest CRC incidence and diabetes prevalence in Canada, we assessed and compared the risk elevation of CRC for males and females with diabetes, overall and by anatomic subsite. METHODS: A population-based retrospective cohort study including a study sample of 122,228 individuals aged ≥30 years was conducted using administrative health databases over a 10.5-year period (October 1, 1996 to March 31, 2007). Hazard ratios were estimated using Cox proportional hazard models. RESULTS: In comparison with non-diabetes counterparts, both males and females with diabetes were at a significantly elevated risk of overall CRC, with corresponding hazard ratios of 1.38 and 1.52, respectively. For males, diabetes significantly increased the risk of proximal and distal colon cancers, but not of rectal cancer. For females, diabetes significantly increased the risk of proximal colon and rectal cancers, but not of distal colon cancer. The results suggest that there is a stronger association between diabetes and CRC for females than for males, and the association did not change after adjusting for overweight/obesity. CONCLUSIONS: Diabetes led to a greater risk of CRC in both the male and female population in NL. Risk was subsite-specific and varied by sex. Future research should examine reasons for the observed diabetes-associated CRC risk to support CRC prevention strategies among the diabetes population