Endocrine and physical determinants of bone mass in late postmenopause

To analyze the relative contribution of endocrine and physical factors to bone mineral density (BMD) in late menopause, we studied biochemical markers of bone turnover as well as sex and calciotropic hormones in 53 women (mean age 61 +/- 5.3 years), 5 to 23 years after natural menopause. BMD was measured at the lumbar spine and proximal femur by dual energy radiography. Stepwise regression analysis showed that age and PTH levels were the two major factors that significantly accounted for spinal BMD, with a final r2 = 0.27. Plasma androstenedione was the only other variable that contributed, albeit not significantly, to spine BMD increasing the r2 by 2%. Conversely, body mass was the main contributor to femoral BMD at all sites. While serum calcium and urinary hydroxyproline were significant determinants of neck BMD, urinary hydroxyproline and age provided significant source of variation for trochanteric BMD, and circulating FSH for BMD in the Ward's area. The final models gave r2 values of 0.35, 0.31, and 0.23, for neck, trochanter and Ward's areas, respectively. Thus, determinants of bone density differentially affect the vertebral and proximal femoral sites. While increasing age and PTH, probably reflecting a subclinical vitamin D deficiency, explain a decreased vertebral bone density, body mass appears to affect mostly the proximal femur. Circulating androgens play a secondary role. A persistently increased bone turnover state is conducive to lower bone density in late postmenopausal women.