Obesity Has a Stronger Relationship with Colorectal Cancer in Postmenopausal Women than Premenopausal Women

Background: To examine the relationship between obesity measured by waist circumference (WC) and body mass index (BMI) and the incidence of colorectal cancer in premenopausal and postmenopausal women. Methods: A total of 1,418,180 premenopausal and 4,854,187 postmenopausal women without cancer at baseline and ages over 40 were identified using the Korean National Health Insurance System Cohort during 2009 to 2014. The hazard ratio (HR) for colorectal cancer incidence was assessed according to menopausal state using Cox proportional hazards models. Results: During a mean follow-up period of 7.2 years, 7,094 and 57,449 colorectal cancer cases occurred in premenopausal and postmenopausal women, respectively. Compared with the reference group (WC 65–75), the HRs [95% confidence interval (CI)] of colorectal cancer in WC <65, 75–85, 85–95, and >95 groups were 1.01 (0.91–1.11), 1.02 (0.97–1.07), 1.09 (1.00–1.18), and 1.31 (1.12–1.52), respectively, in premenopausal women and 1.01 (0.95–1.17), 1.09 (1.07–1.12), 1.19 (1.00–1.18), and 1.30 (1.25–1.35), respectively, in postmenopausal women. Compared with the reference group (BMI 18.5–22.9), HRs (95% CI) for colorectal cancer in BMI <18.5, 23–25, 25–30, and >30 groups were 0.99 (0.87–1.14), 0.99 (0.94–1.06), 0.98 (0.92–1.04), and 1.06 (0.92–1.20), respectively, in premenopausal women. In postmenopausal women, those values were 0.99 (0.93–1.05), 1.05 (1.03–1.08), 1.11 (1.09–1.13), and 1.20 (1.16–1.25), respectively. Conclusions: WC is associated with the risk of colorectal cancer in both groups of women, but this association was stronger in postmenopausal women than in premenopausal women. BMI increased the incidence of colorectal cancer only in postmenopausal women Impact: Obesity has a stronger relationship with colorectal cancer in postmenopausal women than in premenopausal women.