Physiologic age modifies the association between visceral fat predominance and urinary calcium excretion in adults with nephrolithiasis.

Although adiposity is associated with kidney stone disease, the relationship between abdominal fat distribution and urinary calcium excretion remains unclear. We investigated whether the CT-derived visceral-to-subcutaneous fat ratio (VSR) was associated with 24-hour urinary calcium excretion and whether physiologic age modified this association. This retrospective cross-sectional study included 308 adults with nephrolithiasis who underwent preoperative CT, stone removal, and postoperative metabolic evaluation. Participants were stratified into prespecified younger (men aged < 50 years and premenopausal women) and older (men aged ≥ 50 years and postmenopausal women) physiologic-age groups. Multivariable linear regression assessed the association between VSR and urinary calcium excretion and its modification by physiologic age. Results showed that VSR was not associated with urinary calcium excretion in the overall cohort, but its association differed significantly by physiologic age (P for interaction < 0.001). Among younger participants, each 1-unit higher VSR was associated with 2.07 mmol/day greater urinary calcium excretion (95% CI, 1.23-2.90), whereas no significant association was observed in the older group. These findings suggest that the metabolic relevance of visceral fat predominance differs by physiologic age, with a significant association observed only in younger adults. Prospective studies are needed to confirm these findings and determine their clinical implications.