Mediation of calcium-to-phosphorus ratio in the association between kidney stones and bone mineral density in the femoral neck: a cross-sectional study based on the National Health and Nutrition Examination Survey (NHANES)

BackgroundKidney stones, a prevalent urological disorder, are increasingly associated with potential skeletal health issues, including reduced bone mineral density (BMD) and an elevated risk of osteoporosis. However, the underlying mechanisms and subgroup-specific associations have not yet been adequately explored. MethodsThis study used data from a nationally representative survey with a weighted complex sampling design. A total of 6,464 participants were enrolled in the study. We performed weighted and unweighted comparative analyses, multivariate linear regression, mediation analysis, and subgroup evaluations to examine the association between kidney stones and BMD of the femoral neck and lumbar spine. Potential mediators, including the systemic immune-inflammation index (SII), estimated glomerular filtration rate (eGFR), and calcium-to-phosphorus (CaP) ratio, were investigated. ResultsThe presence of kidney stones was significantly associated with lower femoral neck BMD ({beta} =-0.015, p = 0.046) after adjusting for confounding factors. The CaP ratio was identified as a significant mediator (average causal mediation effect [ACME] = 0.00077, p = 0.028), whereas the SII and eGFR did not show significant mediating effects. Stratified analyses revealed stronger associations in participants aged < 50 years and in those without chronic kidney disease (CKD). No significant interactions according to gender were detected. ConclusionKidney stones are independently associated with reduced BMD, which is partially mediated by altered calcium-phosphorus homeostasis. These findings highlight the importance of monitoring bone health in patients with kidney stones, particularly in younger and non-CKD populations, and suggest that dietary mineral balance may play a critical role in bone-stone interaction.