Waist-to-Hip Ratio Outperforms Body Mass Index for Colorectal Cancer Risk Prediction: The Nanjing Chronic Disease Cohort Study

Background: Colorectal cancer (CRC) incidence is rising in China. Although obesity is a risk factor, body mass index (BMI) does not capture fat distribution. Central obesity indicators, particularly waist-to-hip ratio (WHR) and waist-to-hip ratio adjusted for BMI (WHRadjBMI), may better reflect visceral adiposity implicated in colorectal carcinogenesis. Methods: We conducted a prospective cohort study among 120,348 Chinese adults from the Nanjing Chronic Disease Cohort (NCDC). Baseline measures included BMI, waist circumference (WC), WHR, and WHRadjBMI. Incident CRC cases were ascertained via linkage to disease surveillance and health insurance databases. Cox regression estimated HRs and 95% CIs. Mutual adjustment and population attributable fraction (PAF) analyses were performed. Results: During 3.0 years of follow-up, 175 CRC cases occurred. Elevated WHR showed the strongest association (HR 1.90, 95% CI 1.33–2.73), followed by WHRadjBMI (HR 1.65) and WC (HR 1.60). BMI ≥ 24 kg/m2 was not significant (HR 1.33, p = 0.076). In mutual adjustment, BMI’s association was attenuated, whereas WHR remained significant (HR 1.66, p = 0.015). WHR had the highest PAF (24.6%). The association was comparable in men and women. Conclusions: Central obesity measures, particularly WHR, demonstrated stronger associations with CRC risk than BMI in Chinese adults. Assessing central fat distribution may provide additional value for CRC risk stratification.