Femoral bone mineral density and mortality risk in postmenopausal women: a National Health and Nutrition Examination Survey cohort study

OBJECTIVE: Osteoporosis is highly prevalent among postmenopausal women. While previous studies have primarily focused on the relationship between bone mineral density (BMD) and fracture risk, the prognostic value of BMD with regard to mortality remains unclear. METHODS: A total of 2,977 postmenopausal women from the National Health and Nutrition Examination Survey (2005-2018) were included in this study. BMD at four femoral sites was assessed using dual-energy x-ray absorptiometry. The associations between BMD, osteoporotic fractures, and mortality were evaluated using Kaplan-Meier curves, receiver operating characteristic analysis, and multivariate Cox regression. Restricted cubic splines were applied to explore nonlinear relationships, and subgroup analyses were performed to evaluate the robustness of the results. RESULTS: Kaplan-Meier analysis revealed that mortality risk was significantly elevated when femoral BMD reached the osteoporotic threshold or in the presence of osteoporotic fractures (P < 0.001). Receiver operating characteristic curve analysis showed that the area under the curve for BMD at all femoral sites was greater than that for body mass index (area under the curve = 0.591). After full adjustment, osteoporosis was associated with a 47% increased risk of mortality (hazard ratio = 1.47, 95% CI: 1.16-1.86). Site-specific BMD was inversely correlated with mortality risk (all P <0.001). The restricted cubic splines plots demonstrated a stronger inverse association between increased BMD and mortality risk within specific ranges: 0.46-0.71 g/cm² for total femur BMD and 0.33-0.54 g/cm² for trochanter BMD. CONCLUSIONS: Femoral BMD and osteoporosis are independent predictors of all-cause mortality in postmenopausal women. The inverse relationship between BMD and mortality risk is more pronounced within specific BMD ranges, which may provide valuable insights for mortality risk stratification and clinical decision-making in this population.