Context: Although estrogen clearly plays a central role in regulating bone mass in women, studies in men have suggested that there may be a threshold bioavailable (bio) estradiol (E2) level below which aging men begin to lose bone and that the threshold for estrogen deficiency in cortical bone may be considerably lower than that in trabecular bone. There are no data testing this in women. Objective: Our objective was to assess volumetric bone mineral density (vBMD) and bone geometry by quantitative computed tomography and relate these to circulating bio E2 and bio testosterone levels. Design: We studied a cross-sectional, age-stratified population sample of 235 women (age, 21-97 yr). Results: vBMD/structural parameters were not related to sex steroid levels in young premenopausal women (age, 20-39 yr) with a median bio E 2 level of 17 pg/ml (63 pmol/liter). By contrast, bio E2 and bio testosterone levels were both significantly associated with trabecular and cortical vBMD and cortical area at multiple sites in late postmenopausal women (age ≥ 60 yr) who had a median bio E2 level of 3 pg/ml (11 pmol/liter). Late premenopausal and early postmenopausal women (age, 40-59 yr) with an intermediate median bio E2 level of 11 pg/ml (42 pmol/liter) showed age-adjusted correlations of bio E2 levels with trabecular but not with cortical vBMD. Conclusions: In women, bio E2 levels are associated with vBMD and some structural bone parameters at low but not high bio E2 levels. Similar to findings in men, the threshold for estrogen deficiency in cortical bone in women appears to be lower than that in trabecular bone.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism
- Clinical Biochemistry
- Biochemistry, medical