Increased risk of colorectal cancer in type 2 diabetes is independent of diet quality.
BACKGROUND
Poor diet increases the risk of both colorectal cancer and type 2 diabetes. We investigated the role of diet in the association between diabetes and colorectal cancer.


METHODS
We analyzed data from 484,020 individuals, aged 50-71 years who participated in the prospective National Institutes of Health-AARP Diet and Health Study and were cancer free at baseline (1995-1996). History of diabetes was self-reported. Diet quality was measured with the Healthy Eating Index-2005 (HEI-2005), using a self-administered food-frequency questionnaire. Cox regression models were constructed to estimate the hazard ratios (HR) and 95% confidence intervals (CI) of first primary incident colorectal cancer, overall and by anatomical location.


RESULTS
During an average follow-up of 9.2 years, we identified 7,598 new cases of colorectal cancer. After controlling for non-dietary confounders, diabetes was associated with increased risk of colorectal cancer (HR 1.27, 95% CI: 1.18, 1.36). Further adjustment for diet quality did not attenuate this association. Diabetes was associated with a HR of 1.23 (95% CI: 1.07, 1.40) in individuals with good diet (quartile 4 of HEI-2005) and 1.58 (95% CI: 1.34, 1.86) in those with poor diet (quartile 1 of HEI-2005), compared to those with no diabetes and good diet. Moreover, diabetes was associated with a stronger risk of proximal than distal colon cancer (HR: 1.33 vs. HR: 1.20), while poor diet was associated with a weaker risk of proximal colon cancer (HR: 1.18 vs. HR: 1.46).


CONCLUSIONS
Diabetes and poor diet, independently and additively are associated with the increased risk of colorectal cancer.
Division of Health Behavior Research, Department of Medicine, Washington University School of Medicine, Saint Louis, Missouri, United States of America.
Soghra
S
Jarvandi
Nicholas O
NO
Davidson
Mario
M
Schootman
D000368:Aged; D015179:Colorectal Neoplasms / Q000453:epidemiology* / Q000209:etiology*; D003924:Diabetes Mellitus, Type 2 / Q000150:complications*; D004032:Diet; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012306:Risk