Abstract
CONTEXT: Considerable evidence indicates that osteoblasts and adipocytes share a common progenitor cell in the bone marrow that is capable of mutually exclusive differentiation into the cell lineages responsible for bone and fat formation. OBJECTIVE: The purpose of this study was to examine the relation between bone acquisition and changes in marrow adiposity. DESIGN: This was a longitudinal study. OUTCOME MEASURES AND SUBJECTS: Computed tomography measurements of femoral cortical bone area (CBA), cross-sectional area (CSA), and marrow density, and dual-energy x-ray absorptiometry (DXA) measurements of total body fat and lean mass (LM) were obtained in 39 healthy females (15-20 yr of age) at baseline and 18-24 months later. RESULTS: Marrow adiposity was inversely related to CBA at baseline and follow-up (r = 0.39 and 0.33; P = 0.015 and 0.039, respectively) but was not associated to CSA (r = 0.19 and 0.17; P = 0.24 and 0.32, respectively). The association between marrow fat and CBA persisted, even after controlling for body mass and DXA values of LM and femoral CSA. Gains in CBA during the course of the study were related to decreases in marrow fat (r = 0.41; P = 0.009), a relation that persisted, even after accounting for changes in bone size. Marrow fat was not associated to anthropometric measures or DXA values of body fat and LM (all r's between -0.15 and 0.19; P > 0.05). CONCLUSIONS: Bone acquisition in the appendicular skeleton of healthy young females is inversely related to changes in marrow adiposity. These results provide support for the growing body of evidence indicating an inversely coupled relationship between osteogenesis and adipogenesis in the skeleton.