PURPOSE: Osteoporosis imposes significant burdens. Early detection of high-risk individuals through simple indicators can greatly improve prognosis. Red cell distribution width (RDW), a standard component of a complete blood count, shows promise, yet remains underexplored. This cross-sectional study aimed to investigate the association between RDW and femoral neck and spinal bone mineral density (BMD). METHODS: Participants aged 20-79 years from the 2005-2010, 2013-2014, and 2017-2020 cycles of the National Health and Nutrition Examination Survey (NHANES) were included. BMD was measured using dual-energy X-ray absorptiometry (DXA). RESULTS: A total of 13,029 participants were included, comprising 6684 men, 3238 postmenopausal women, and 3107 premenopausal women, with the sample weighted to represent 98,712,128 people. After adjusting for covariates, RDW exhibited a negative association with femoral neck BMD in both men (β = -0.006
95% CI: -0.010 to -0.002
p = 0.0053) and postmenopausal women (β = -0.005
95% CI: -0.010 to -0.000
p = 0.0413). Subgroup and sensitivity analyses supported the robustness of these findings. A negative association between RDW and spinal BMD in men approached significance (β = -0.004
95% CI: -0.008 to 0.000
p = 0.0557). Persistent trends were observed for RDW with spinal BMD in postmenopausal women and with both femoral neck and spinal BMD in premenopausal women. CONCLUSIONS: Our study suggests a negative association between RDW and femoral neck BMD in both men and postmenopausal women. These findings highlight the potential of RDW as a marker for identifying individuals at higher risk of osteoporosis.