Submitted on June 3, 2005
Accepted on December 29, 2005
Relationship of Fat Mass and Serum Estradiol with Lower Extremity Bone in Persons with Chronic Spinal Cord Injury
William A Bauman1*, Ann M Spungen1, Jack Wang2, Richard N Pierson, Jr2, and Ernest Schwartz3
1 Department of Veterans Affairs Rehabilitation Research and Development Center of Excellence, Veterans Affairs Medical Center, Bronx, NY, USA; Department of Medicine & Rehabilitation Medicine, Mount Sinai School of Medicine, New York, NY, USA
2 Body Composition Unit, Columbia University-St. Lukes and Roosevelt Hospital Center, New York, NY, USA
3 Department of Veterans Affairs Rehabilitation Research and Development Center of Excellence, Veterans Affairs Medical Center, Bronx, NY, USA; Spinal Cord Damage Research Center, James J. Peters Veterans Affairs Medical Center, Bronx, NY, USA
* To whom correspondence should be addressed. E-mail: wabauman{at}earthlink.net.
In the 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 (r2=0.49, P<0.05; r2=0.45, P=0.05), leg fat mass (r2=0.76, P<0.0005; r2=0.69, P=0.005), and serum estradiol (r2=0.40, P=0.05; r2=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, r2=0.76, P=0.008; F=50.87, r2=0.86, P<0.0001). In the able-bodied twins, leg lean mass correlated with leg BMD and BMC (r2=0.58, P=0.01; r2=0.87, P=0.0001). Using within pair differences, significant correlations were found for leg lean mass loss with leg BMD loss (r2=0.56, P=0.01) or leg BMC loss (r2=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.
