Insulin resistance, central obesity, and risk of colorectal adenomas

BACKGROUND: Increasing evidence supports insulin resistance (IR) as the underpinning of the obesity-colorectal neoplasia link. The homeostasis model assessment-IR (HOMA-IR) is a widely accepted index of evolving hyperinsulinemia and early IR. Studies of the relation between HOMA-IR and colorectal adenomas are limited. Therefore, the authors sought to determine the associations of HOMA-IR and central obesity (waist to hip ratio [WHR]) with risk of colorectal adenomas in a screening colonoscopy-based study. METHODS: The authors collected lifestyle information and fasting blood samples from 1222 participants (320 incident adenoma cases and 902 without adenomas) before their screening colonoscopies. Unconditional logistic regression models were used to assess risk associations. RESULTS: In multivariate analysis of participants (n = 1093) reporting no antidiabetic medication use, those in the top quartile of WHR were twice as likely (odds ratio [OR], 2.18; 95% confidence interval [CI], 1.33-3.57; P-trend =.003) and those in the top quartile of HOMA-IR were 63% more likely (OR, 1.63; 95% CI, 1.09-2.44; P-trend = .01) to have adenomas compared with those in the bottom quartiles. Stratified analysis revealed a statistically significant interaction between HOMA-IR and sex (P-interaction = .04), with the association largely limited to men; compared with those in the bottom tertile, men in the top tertile of HOMA-IR were twice more likely to have adenomas (OR, 2.11; 95% CI, 1.18-3.78; P-trend = .01). CONCLUSIONS: The results support central obesity and insulin resistance, particularly in men, as important risk factors for the development of early colorectal neoplasia.