Relationship between serum 1,25-dihydroxyvitamin D and bone loss in postmenopausal women

Objective: To study the correlations between loss of activity and/or amont of serum 1,25-dihydroxyvitamin D(1,25(OH)2D) and 25-dihydroxyvitamin D(1,25(OH)2D) and bone loss in postmenopausal women, in order to reveal the possible pathophysiology of postmenopausal osteoporosis.

Methods: The serum levels of 1,25 (OH)2D, 25 (OH) D, PTH, and E2 in 57 postmenopausal women with osteoporosis and 37 postmenopausal women without osteoporosis were measured by radioimmunology. Their Dpd/Cr in urine was measured by ELISA. The bone mineral density (BMD) at lumbar spine (L2-4) was measured in each subject by DEXA.

Results: The serum 1,25(OH)2D in postmenopausal oeteoporotic women and non-osteoporotic women were 18 pg/ml +/- 6 pg/ml and 31 pg/ml +/- 14 pg/ml respectively (P < 0.01) The serum 25 (OH)2D in postmenopausal oeteoporotic women and non-osteoporotic women were 32 ng/ml +/- 9 ng/ml and 46 ng/ml +/- 17 ng/ml respectively (P < 0.01). Postmenopausal osteoporotic women had a lower estrogen concentration (P < 0.01), higher serum parathyroid hormone (PTH) (P < 0.01) and higher urinary Dpd/Cr level (P < 0.01). The level of serum 1,25(OH)2D was highly correlated with BMD in L2-4 for postmenopausal women (r = 0.693, P < 0.001). There was a close relationship between the serum level of 1,25(OH)2D and serum level of 25(OH)2D, suggesting an association between the two factors.

Conclusions: The lower bone mass density was associated with lower level of serum 1,25-dihydroxyvitamin D, accompanied by reduced serum estrogen and elevated serum PTH in postmenopausal women. Those may be among the important pathphysiological changes of postmenopausal osteoporosis.