Body Roundness Index and Incident Colorectal Cancer Risk: A Nationwide Population-Based Cohort Study

Background/Objectives: Colorectal cancer (CRC) is among the most common cancers in Korea, and visceral adiposity is an established modifiable risk factor. The body roundness index (BRI), derived from waist circumference and height, estimates visceral adipose tissue more accurately than the body mass index (BMI) alone. We investigated the longitudinal association between the BRI and incident CRC in a large Korean national cohort. Methods: A nationwide cohort of 4,492,697 adults aged ≥20 years who participated in the 2012 Korean National Health Insurance Service health check-up was followed through December 2023 (mean 10.32 years). BRI values were categorized into quartiles (Q1-Q4). After applying a 1-year lag period, Cox proportional hazards regression estimated hazard ratios (HRs) and 95% confidence intervals (CIs), adjusting for age, sex, smoking, alcohol consumption, exercise, income, diabetes, hypertension, hypercholesterolemia, and chronic kidney disease. Subgroup and site-specific analyses were also performed. Results: During 46,382,686 person-years of follow-up, 57,644 incident CRCs were diagnosed. A higher BRI was independently and dose-dependently associated with CRC risk (Q4 vs. Q1: aHR 1.104, 95% CI 1.075-1.135; p for trend < 0.001). The association was significantly stronger in men (Q4 aHR 1.352, 95% CI 1.302-1.404) than in women (Q4 aHR 0.891, 95% CI 0.858-0.925; p for interaction < 0.001) and most pronounced in middle-aged adults (40-64 years). Site-specific analyses revealed a proximal-to-distal gradient: proximal colon (Q4 aHR 1.363), distal colon (Q4 aHR 1.244), and rectum (Q4 aHR 1.070). Conclusions: A higher BRI is independently and dose-dependently associated with increased CRC incidence in Korean adults, particularly in men and those with general obesity. The BRI may serve as a practical complement to the BMI for CRC risk stratification in populations with a high prevalence of metabolic obesity.