Regional climate and lifestyle are key drivers of urolithiasis, yet long-term data from subtropical coastal regions in China are limited. This study investigated the epidemiological characteristics and dynamic age-sex associations of stone composition in Xiamen, a major maritime city in Southern China. We analyzed 3901 patients with urolithiasis at a tertiary center between March 2012 and June 2025. Stone components were identified using Fourier-transform infrared spectroscopy. Beyond standard categorical analysis, we employed restricted cubic spline (RCS) models to describe the precise nonlinear associations between age, sex, and the risk of major stone types. Calcium oxalate (CaOx) was the predominant component (73.9%), though mixed stones were remarkably frequent (82.4%). We observed robust sex-specific profiles: men showed higher rates of CaOx and uric acid (UA) stones, whereas women were more prone to calcium phosphate (CaP) and magnesium ammonium phosphate (MgP/infection) stones. RCS analysis revealed distinct risk trajectories: CaOx followed an inverted U-shaped pattern peaking in midlife (45–50 years); CaP risk generally declined with age. Notably, UA risk demonstrated a J-shaped escalation, rising exponentially after age 50, particularly in men. In women, MgP risk followed a U-shaped curve, increasing sharply after age 70. Despite the subtropical setting, no significant seasonal variations were found, suggesting that the stable maritime climate may dampen the thermal drivers of stone formation seen in continental regions. Urinary stone composition in this coastal population follows complex, sex-dependent, and nonlinear age trajectories. The late-life surge in UA stones among men and infection stones among women highlights the need for stratified, age-specific metabolic and clinical management. These findings provide a data-driven framework for personalized urolithiasis prevention in Southern China.
Yan et al. (2026) studied this question.