Joint Associations of Abdominal Obesity, General Obesity, and Smoking with Bladder Cancer Risk Among Postmenopausal Women: A Nationwide Cohort Study

BACKGROUND: The independent and joint associations of waist circumference (WC), body mass index (BMI), and smoking with bladder cancer risk in postmenopausal women remain unclear. We investigated these associations in a nationwide cohort. METHODS: This study included 1,336,820 postmenopausal Korean women without prior cancer from the national health screening program in 2009 who were followed until 2022. Abdominal obesity was defined as WC ≥85 cm and general obesity as BMI ≥25 kg/m², according to the Korean criteria. Multivariable Cox proportional hazards models estimated hazard ratios (HRs) and 95% confidence intervals (CIs). RESULTS: Over a median follow-up of 12.4 years, 2,315 incident bladder cancer cases were identified. Smoking was independently associated with an increased risk of bladder cancer (HR, 95% CI: 1.83, 1.53-2.19), compared with never smoking. Among individuals who never smoked, abdominal obesity and general obesity were associated with increased risk (HR, 95% CI: 1.17, 1.07-1.28 and 1.09, 1.005-1.19). In joint-effect analyses, individuals who ever smoked and had obesity exhibited the highest risk compared with individuals who never smoked without obesity (abdominal: HR, 95% CI: 2.27, 1.71-3.01; general: 2.36, 1.81-3.09). CONCLUSIONS: Both abdominal and general obesity were associated with higher bladder cancer risk in postmenopausal women, with substantially greater risk among those with concurrent smoking exposure. These findings emphasize the importance of obesity prevention and smoking cessation in reducing risk in this underrecognized population. IMPACT: Targeting abdominal and general obesity, particularly among individuals who smoked, may meaningfully lower bladder cancer risk in postmenopausal women.