Osteoporosis is associated with increased marrow fat content and decreased marrow fat unsaturation: A proton MR spectroscopy study

PURPOSE: To use proton magnetic resonance spectroscopy ((1)H-MRS) to evaluate vertebral marrow fat, and to determine whether bone density correlates with fat content and fat unsaturation levels in postmenopausal women. MATERIALS AND METHODS: Fifty-three women (mean age = 70 years) underwent dual energy x-ray absorptiometry and (1)H-MRS, and 12 young female controls (mean age = 28 years) underwent (1)H-MRS of the lumber spine. Water and lipid peak amplitudes were measured to calculate fat content and fat unsaturation index. Spearman's correlation tests and a t-test comparison of means were applied. RESULTS: (1)H-MRS was successful in 15 normal, 15 osteopenic, and 20 osteoporotic subjects, and in all controls. Marrow fat content was significantly elevated in osteoporotic (65.5% +/- 10%) and osteopenic (63.5% +/- 9.3%) subjects compared to normal subjects (56.3% +/- 11.2%) and young controls (29% +/- 9.6%). The fat unsaturation index was significantly decreased in osteoporotic (0.091 +/- 0.013) and osteopenic (0.097 +/- 0.014) subjects compared to normal subjects (0.114 +/- 0.016) and young controls (0.127 +/- 0.031). A good inverse correlation was observed between the fat content and the unsaturation index (r(s) = -0.53, P < 0.0001). CONCLUSION: Osteoporosis is associated with increased marrow fat. As marrow fat increases, saturated lipids appear to increase preferentially to unsaturated lipids.