Diabetes and risk of incident colorectal cancer in a prospective cohort of women.
OBJECTIVE
To determine whether accounting for the time dynamics of diabetes exposure will change the risk estimates for colorectal cancer.


METHODS
We analyzed data from the 45, 516 women enrolled in the BCDDP follow-up cohort study. We used proportional hazards regression to obtain multivariable-adjusted risk estimates for incident colorectal cancer for prevalent diabetes at baseline and diabetes as a time-dependent variable.


RESULTS
Subjects with diabetes had a statistically significant increased risk of colorectal cancer compared to subjects without diabetes (RR = 1.60, 95% CI 1.18-2.18). When we defined exposure as duration of diabetes exposure at cohort exit, we found that in the first 4 years after diagnosis risk was essentially the same as in those never having had a diagnosis of diabetes. For those who had been diagnosed between 4 and 8 years previously, however, we observed a RR of 2.36 (95% CI 0.96-5.79), while longer duration of exposure was associated with smaller and then no change in risk compared to those without a diagnosis of diabetes.


CONCLUSIONS
These results are consistent with the theory that hyperinsulinemia can explain, at least in part, the association of diabetes with colorectal cancer, but in a time-dependent manner.
Flood
Andrew
A
Division of Epidemiology and Community Health, University of Minnesota, 1300 South Second Street, Suite 300, Minneapolis, MN 55454, USA. aflood009@umn.edu
Strayer
Lori
L
Schairer
Catherine
C
Schatzkin
Arthur
A
D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000453:epidemiology*; D003924:Diabetes Mellitus, Type 2 / Q000453:epidemiology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D006946:Hyperinsulinism / Q000453:epidemiology; D015994:Incidence; D008137:Longitudinal Studies; D008875:Middle Aged; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D014481:United States / Q000453:epidemiology
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