Bone marrow fat is inversely related to cortical bone in young and old subjects.

OBJECTIVE Recent studies suggest a close local link between bone marrow adiposity and endosteal bone formation. Using magnetic resonance imaging, we examined whether the relation between the amount of marrow fat and cortical bone is present at multiple sites along the diaphyses of the long bones of young and old males and females. DESIGN The relations between values for cortical bone area and percent marrow fat in each 5-mm section along the midthird of both femoral shafts were determined using magnetic resonance imaging in eight healthy young (aged <25 yr), and nine healthy old (aged >55 yr) men and women. RESULTS Strong inverse correlations were observed between values for cortical bone area and percent marrow fat along the shafts of all 34 femurs; r values between -0.54 to -0.97; all P values = 0.01-0.0001. The strength of this local association was comparable in the young and the elderly and in males and females. CONCLUSION Our results underscore the strength of the local connections between bone and marrow adiposity. Increasing our understanding of the mechanism for this association could lead to better diagnosis and treatment approaches for osteoporosis.