Liver fat fraction negatively correlates with lumbar BMD in normal body mass index postmenopausal women: mediated by bone marrow fat.

BACKGROUND: The liver-bone axis plays a key role in lipid metabolism and endocrine regulation. However, the relationship between fatty liver disease and both the level and longitudinal changes of bone mineral density (BMD) remains inconclusive. This study aimed to explore the correlation of liver fat with lumbar BMD and bone marrow fat in postmenopausal women. METHODS: In this cross-sectional study, conducted between May 2023 and December 2025, 118 postmenopausal women were included and stratified into 2 groups based on their BMI. All participants underwent quantitative computed tomography (QCT) to assess lumbar BMD and liver fat fraction, and underwent MRI using the mDixon-Quant sequence to assess lumbar proton density fat fraction (PDFF). Correlation analysis, linear regression, and mediation analysis were performed to evaluate the relationships among liver fat, lumbar PDFF, and BMD. Logistic regression analysis was used to assess the impact of liver fat on osteoporosis. RESULTS: In the normal-BMI group, the liver fat fraction was correlated negatively with BMD [β = -0.368, 95% confidence interval (CI): -0.605 to -0.131, P = 0.003] and positively with lumbar PDFF (β = 0.335, 95% CI: 0.064 to 0.607, P = 0.016) after adjusting for age BMI, and visceral fat area. The liver fat fraction was also identified as an associated factor for osteoporosis [odds ratio (OR) = 1.345, 95% CI: 1.065 to 1.699, P = 0.013] in the normal-BMI group. Mediation analysis demonstrated that lumbar PDFF played a crucial intermediary role (38.6%) in the relationship between liver fat fraction and BMD. However, in the higher BMI group, no correlation was found between liver fat and BMD or lumbar PDFF. CONCLUSION: Liver fat fraction is independently associated with lower lumbar BMD in normal-BMI postmenopausal women, partially mediated by bone marrow fat, suggesting it may serve as a potential extra-osseous imaging biomarker for osteoporosis risk.