Lack of Association Between Insulin Sensitivity and Colorectal Adenoma Risk

Abstract

Insulin resistance is thought to mediate the association between obesity and colorectal neoplasia, but no prior studies have assessed stimulated insulin sensitivity as a risk factor for colorectal neoplasia. This prospective study examined the association between insulin sensitivity measured directly using the frequently sampled intravenous glucose tolerance test (FSIGT) and later risk of colorectal adenomas. Among participants with a range of glucose tolerance levels enrolled in the Insulin Resistance Atherosclerosis Study, colonoscopies were conducted on 600 participants ages ≥50 yr, regardless of symptoms, about 10 yr after the first FSIGT and 5 yr after the second. Multiple logistic regression analyses were used. Within this cohort, diabetes was not associated with colorectal adenoma risk [∼10 yr prior to colonoscopy adjusted odds ratio (OR_adj) 1.00; 95% confidence interval (CI), 0.62–1.62 or ∼5 yr prior to colonoscopy OR_adj 0.96; 95% CI, 0.62–1.50]. Among non-diabetic participants, insulin sensitivity was not associated with colorectal adenoma risk at either prior study visit [lowest vs. highest insulin sensitivity, ∼10 yr prior to colonoscopy OR_adj 0.93; 95% CI 0.50–1.71 and ∼5 yr prior to colonscopy OR_adj 0.74; 95% CI, 0.38–1.46]. These results suggest that factors other than insulin sensitivity mediate the relationship between obesity and colorectal neoplasia.

ACKNOWLEDGMENTS

The Colorectal Ancillary Study to the Insulin Resistance and Atherosclerosis Study Cohort was funded by grants from the National Cancer Institute (1R01CA88007, NIH R01 CA 88008). We are grateful to the study participants and the staff at the clinical centers.

Notes

*Pearson χ² test.

¹ n = 572 with BMI measures obtained.

¹Adjusted for age at colonoscopy and sex using logistic regression.

²Adjusted for age at colonoscopy, center, race/ethnicity, smoking status at colonoscopy, sex, and previous screening (self-reported none, yes without polyp(s), yes with polyp(s)) using logistic regression.

³ n = 599.

⁴As the range of insulin sensitivity is limited in diabetics, analyses were only reported among non-diabetic participants.

⁵ n = 434.

⁶ n = 571.

⁷ n = 573.

⁸ n = 576.

⁹ n = 360.