EFFECTS OF AGE AND ESTROGEN STATUS ON SERUM PARATHYROID-HORMONE LEVELS AND BIOCHEMICAL MARKERS OF BONE TURNOVER IN WOMEN - A POPULATION-BASED STUDY

Although estrogen deficiency is responsible far the increase in bone t urnover in early postmenopausal women, age-related factors, such as th e progressive increase in serum PTH levels, are believed to be respons ible for the increase in bone turnover in elderly women. Whether estro gen deficiency continues to play a role, either directly or indirectly , in the pathogenesis of the increased bone turnover in elderly women remains unclear. Thus, we measured serum PTH, markers of bane turnover , and serum sex steroid levels in a population-based sample of 351 wom en (age range, 21-94 yr), which included 47 postmenopausal women who m ere receiving long term estrogen replacement therapy. Serum PTH increa sed as a function of age when the premenopausal women and the estrogen -deficient postmenopausal women were analyzed together (r = 0.35; P < 0.001). By contrast, this age-related increase in serum PTH was elimin ated in the postmenopausal women receiving long term estrogen therapy, which also resulted in a similar suppression of markers of bone forma tion and resorption in bath the early (less than or equal to 20 yr) an d late (>20 yr) postmenopausal women. By multivariate analysis, serum 25-hydroxyvitamin D levels were highly predictive of serum PTH levels regardless of menopausal status, whereas serum estrone levels were pre dictive of markers of bone resorption in the postmenopausal women. We conclude that estrogen deficiency may be responsible not only for the increase in bone turnover in early postmenopausal women, but also indi rectly for the secondary hyperparathyroidism and increase in bone turn over found in late postmenopausal women. Residual serum estrogen level s are important determinants of bone resorption in postmenopausal wome n.