Measures of bioavailable serum testosterone and estradiol and their relationships with muscle mass, muscle strength and bone mineral density in postmenopausal women: a cross-sectional study.

OBJECTIVE: The physiologic role of circulating endogenous testosterone and estrogen concentrations in relation to lean body mass (LBM) and muscle strength is not as well documented in postmenopausal women as in elderly men.
DESIGN: Three hundred and twenty-nine healthy postmenopausal women were randomly selected from a general practice population-based sample aged between 55 and 85 years.
METHODS: Total testosterone and estrogen (TT and TE) and sex hormone-binding globulin (SHBG) were determined and estimates of bioavailable testosterone (free androgen index (TT/SHBG, FAI), calculated free testosterone (cFT), and estrogen (TE/SHBG, ESR) were calculated. Examinations included bone mineral density (BMD) of the spine and femoral neck (FN), LBM, maximum quadriceps extension strength (MES) and maximum handgrip strength (MGS), timed up-and-go test (TUGT), osteocalcin (OC), and urinary deoxy-pyridinoline/creatinine (DPyr). Correlations were assessed using Pearson's correlation coefficient (r).
RESULTS: With advancing age, LBM, MES, MGS, BMD, and ESR significantly declined (range r: -0.356 to -0.141) and TUGT, and DPyr significantly increased (range r: 0.135 to 0.282 (P<0.05)). After age-adjustment, LBM, MES, and BMD in spine and FN were significantly related to bioavailable testosterone (range r: 0.146 to 0.193, for cFT, and 0.157 to 0.224, for FAI) and to ESR (range r: 0.162 to 0.273). OC and DPyr were significantly inversely related to ESR (r: -0.154 and -0.144 respectively).
CONCLUSIONS: Age-related loss of LBM, MES and BMD in postmenopausal women is partly dependent on the presence of endogenous bioavailable testosterone and estrogen.