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Relationship of Volumetric Bone Density and Structural Parameters at Different Skeletal Sites to Sex Steroid Levels in Women

Endocrine Research Unit (S.K., B.L.R.), Division of Endocrinology and Metabolism, Department of Internal Medicine; Biomedical Imaging Resource (R.A.R., J.J.C.), Department of Physiology and Biophysics; Department of Health Sciences Research (L.J.M., S.J.A., A.L.O.); and Department of Radiology (P.A.R.), Mayo Clinic College of Medicine, Rochester, Minnesota 55905

Address all correspondence and requests for reprints to: Sundeep Khosla, M.D., Mayo Clinic, Endocrine Research Unit, 200 First Street SW, 5-194 Joseph, Rochester, Minnesota 55905. E-mail: khosla.sundeep{at}mayo.edu.

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 E₂ 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.

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