Body Composition Attenuates the Association Between Serum 25-Hydroxyvitamin D and Bone Mineral Density in Early...

Background/Objectives: Vitamin D plays a central role in calcium and bone homeostasis; however, evidence linking serum 25-hydroxyvitamin D (25(OH)D) to bone mineral density (BMD) in postmenopausal women remains inconsistent. Because body weight and lean mass strongly influence skeletal loading and may also affect circulating 25(OH)D, we aimed to evaluate the association between serum 25(OH)D and bone outcomes in early postmenopausal women and to determine whether body composition attenuates this relationship. Methods: In this cross-sectional study, 120 women within 10 years after natural menopause (59.5 ± 6.3 years) were assessed. Serum 25(OH)D was measured by chemiluminescent immunoassay. Total body areal bone mineral density (total body aBMD, g/cm²) was assessed by DXA, and trabecular volumetric BMD and cortical thickness were obtained using 3D modeling. Associations were examined using Spearman correlations and multivariable linear and logistic regression models adjusted for age, body weight, lean mass, and years since menopause. Results: Median serum 25(OH)D was 23.7 ng/mL [16.7-30.4]. A modest correlation was observed between 25(OH)D and total body aBMD (ρ = 0.22, p = 0.016), but not with trabecular volumetric BMD or cortical thickness. After adjustment, 25(OH)D was not independently associated with total body aBMD (p = 0.144), whereas body weight remained significantly associated (β = 0.27, p = 0.002). In logistic models, body weight (OR = 0.93, 95% CI 0.90-0.96) and lean mass (OR = 0.97, 95% CI 0.95-0.99) were protective against low BMD, while the association with 25(OH)D was modest. Conclusions: In early postmenopause, the association between serum 25(OH)D and BMD is modest and largely attenuated after accounting for body composition. Body weight and lean mass appear to be stronger determinants of bone outcomes than vitamin D status.