Circulating [beta]2 Microglobulin in Relation to Bone Metabolism: Implications for Bone Loss with Aging

The aim of this cross-sectional study was to evaluate the relationships between circulating β^sub 2^ microglobulin (β^sub 2^ m) and bone mineral density (BMD), parameters of bone remodeling, vitamin D metabolites, parathyroid hormone (PTH), estradiol levels, and age in a group of 165 clinically healthy or osteoporotic, but otherwise normal untreated women. In this group of women, systemic β^sub 2^ m correlated with BMD (g/cm^sup 2^) levels for total hip and Ward's triangle (r =-0.298, P < 0.0001; and r =-0.299, P < 0.0001, respectively), but only at the borderline level with BMD at the spine (r =-0.145, P= 0.0604). Serum β^sub 2^ microglobulin markedly correlated with age (r = 0.512, P= 0.0001). β^sub 2^ m levels correlated with indices of bone remodeling, as well as with serum creatinine and estradiol levels. However, after stratification of all analyses by age, body mass index, and serum 25OHD^sub 3^, 1,25(OH)^sub 2^D^sub 3^, PTH, or estradiol levels (using standard multiple regression and stepwise forward regression models), only 25OHD^sub 3^ was found to be an independent predictor of BMD at the hip, including Ward's triangle, as estradiol of BMD at the spine. On the other hand, β^sub 2^ m was not associated with BMD at any of the measured regions. Also, no association was found between serum PTH and BMD values. Therefore, systemic β^sub 2^ m seems to be an indicator of bone remodeling in the course of natural skeletal aging rather than a variable independently predicting bone loss.[PUBLICATION ABSTRACT]