Adiposity Change Patterns and Prostate Cancer Risk: Age- and Smoking-Specific Associations in 1,332,372 Korean Males.

PURPOSE: Evidence linking body mass index (BMI) change to prostate cancer risk remains inconsistent despite known associations between adiposity and prostate carcinogenesis. MATERIALS AND METHODS: We conducted a population-based cohort study of 1,332,372 Korean males who completed health examinations in 2009 and 2013 and were followed through 2017. BMI was classified using Asia-Pacific criteria, and changes between 2009 and 2013 defined 25 groups. Prostate cancers were ascertained by ICD-10 (International Classification of Diseases, 10th Revision) codes. Cox proportional hazards models estimated adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs) controlling for demographics, lifestyle factors, and comorbidities. RESULTS: Over 12.7 million person-years, 9,147 prostate cancers were identified. BMI trajectories displayed distinct risk patterns. Remaining underweight (aHR, 0.76; 95% CI, 0.61 to 0.96) or moving from underweight to normal (aHR, 0.65; 95% CI, 0.47 to 0.91) was associated with lower risk, whereas persistent overweight (aHR, 1.18; 95% CI, 1.10 to 1.27), persistent obesity I (aHR, 1.19; 95% CI, 1.12 to 1.27), and transition from overweight to obesity I (aHR, 1.14; 95% CI, 1.03 to 1.27) were associated with higher risk compared with persistent normal BMI. Among males with obesity I, weight loss to normal BMI was associated with reduced risk compared to persistent obesity I (aHR, 0.63; 95% CI, 0.46 to 0.87). Smoking amplified the adverse associations of persistent overweight and obesity. However, persistent obesity II (≥30 kg/m²) was associated with lower risk among males <60 years (aHR, 0.62; 95% CI, 0.44 to 0.89), though this finding should be interpreted with caution as it may reflect detection bias. CONCLUSIONS: The impact of longitudinal adiposity patterns varied by smoking status and age, supporting personalized, lifestage-specific prevention emphasizing weight management and lifestyle modification.