LAUSR

Purpose: The association between serum 25‐hydroxyvitamin D (25‐OHD) levels and cortical/trabecular bone parameters has been explored in the elderly, but less so in younger adults; body composition may also influence bone parameters across the life span. We aimed to investigate, with peripheral quantitative computerized tomography (pQCT), the relationship between serum 25‐OHD levels and bone geometry and strength and, at the same time, to explore the influence of fat mass and fat‐free mass on bone parameters, for the tibia and radius, in healthy young and elderly adults. Methods: The study involved 149 healthy adults grouped by age: 65 were under 65 years old, and 84 were older. All participants were assessed in terms of: clinical history; serum 25‐OHD levels; fat‐free mass (FFM) and fat mass (FM), measured with DXA; total and cortical bone cross‐sectional area (CSA, CSAc), and trabecular and cortical bone mineral density (BMDt, BMDc); and fracture load x and y for the tibia and radius, measured with pQCT. Results: In the younger group, the association between 25‐OHD levels and bone parameters did not remain as significant for any parameters after multivariate adjustment. In the elderly, 25‐OHD correlated with CSAc (partial R2 = 0.33), fracture load x (partial R2 = 0.54), and fracture load y (partial R2 = 0.46) for the radius, and marginally with BMDt (partial R2 = 0.09; B‐H adjusted p < 0.05 for all) for the tibia. FFM correlated with all bone parameters in both age groups. In the elderly group alone, FM correlated with BMDt at the tibia (r = 0.25, p < 0.05), with CSA at both sites (radius r = −0.25, p < 0.05; tibia r = −0.32, p < 0.001), and with fracture load y on the radius (r = −0.22, p < 0.05). Conclusion: While serum 25‐OHD levels correlated only weakly with bone parameters in younger adults, a significant relationship was observed for elderly people. Fat‐free mass showed positive simple correlation with pQCT‐derived bone parameters in both age groups except with BMDc in the younger group. Further longitudinal studies are needed to clarify these relationships.