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 beta(2) microglobulin (beta(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 beta(2) m correlated with BMD (g/cm(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 beta(2) microglobulin markedly correlated with age (r = 0.512, P = 0.0001). beta(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(3), 1, 25(OH)(2)D(3), PTH, or estradiol levels (using standard multiple regression and stepwise forward regression models), only 25OHD(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, beta(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 beta(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.