Relationship of fat mass and serum estradiol with lower extremity bone in persons with chronic spinal cord injury

1 Department of Veterans Affairs Rehabilitation Research and Development Center of Excellence; 2 Spinal Cord Damage Research Center and 3 Medical, Spinal Cord Injury, and Research Services, Veterans Affairs Medical Center, Bronx; 4 Departments of Medicine and Rehabilitation Medicine, Mount Sinai School of Medicine; and 5 Body Composition Unit, Columbia University-St. Luke's/Roosevelt Hospital Center, New York, New York Submitted 3 June 2005 ; accepted in final form 29 December 2005 In the spinal cord injury (SCI) population, a relationship between adiposity and leg bone has not been reported, nor one between serum estradiol and leg bone mass. A cross-sectional, comparative study of 10 male pairs of monozygotic twins discordant for SCI was performed. Relationships were determined among bone mineral density (BMD), bone mineral content (BMC), lean mass, fat mass, and serum sex steroids. In the twins with SCI, significant relationships were evident between leg BMD or BMC with total body percent fat ( r 2 = 0.49, P < 0.05; r 2 = 0.45, P = 0.05), leg fat mass ( r 2 = 0.76, P < 0.0005; r 2 = 0.69, P = 0.005), and serum estradiol ( r 2 = 0.40, P = 0.05; r 2 = 0.37, P = 0.05). By stepwise regression analysis, in the twins with SCI, leg fat mass was found to be the single most significant predictor of leg BMD or BMC ( F = 12.01, r 2 = 0.76, P = 0.008; F = 50.87, r 2 = 0.86, P < 0.0001). In the able-bodied twins, leg lean mass correlated with leg BMD and BMC ( r 2 = 0.58, P = 0.01; r 2 = 0.87, P = 0.0001). By use of within-pair differences, significant correlations were found for leg lean mass loss with leg BMD loss ( r 2 = 0.56, P = 0.01) or leg BMC loss ( r 2 = 0.64, P = 0.0005). In conclusion, in twins with SCI, significant correlations were observed between fat mass and leg BMD or BMC as well as between serum estradiol values and leg BMD. The magnitude of the leg muscle mass loss was correlated with the magnitude of bone loss. bone mineral density; bone mineral content; lean mass; estrogen; paraplegia Address for reprint requests and other correspondence: W. A. Bauman, Spinal Cord Damage Research Center, Rm. 1E-02, James J. Peters Veterans Affairs Medical Center, 130 West Kingsbridge Rd., Bronx, NY 10468 (e-mail: wabauman{at}earthlink.net )