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Associations among Oral Estrogen Use, Free Testosterone Concentration, and Lean Body Mass among Postmenopausal Women¹

University of Alabama at Birmingham, Department of Nutrition Sciences (B.A.G.), Division of Physiology and Metabolism, and Clinical Nutrition Research Center, and Department of Physiology and Biophysics (L.N.), Birmingham, Alabama 35294-3360

Address all correspondence and requests for reprints to: Barbara A. Gower, Ph.D., Department of Nutrition Sciences, University of Alabama at Birmingham, 427 Webb Building, 1675 University Boulevard, Birmingham, Alabama 35294-3360. E-mail: bgower{at}uab.edu

Circulating concentrations of sex hormone-binding globulin (SHBG) are increased by use of oral estrogen. The objective of this study was to determine whether postmenopausal women who used oral estrogen had higher serum concentrations of SHBG and lower serum concentrations of free testosterone (T) than nonusers, and whether free T was associated with lean body mass, particularly skeletal muscle mass. Subjects were 70 postmenopausal women, 46–55 yr old, 46 of whom used oral estrogen. Total and regional body composition were determined by dual-energy x-ray absorptiometry. Serum concentrations of SHBG, total T, and estradiol (E₂) were determined by RIA. Free T was calculated from concentrations of total T and SHBG. Hormone users had higher serum concentrations of E₂ and SHBG (182.0 ± 58.5 vs. 82.9 ± 41.1 nmol/L, mean ± SD, P < 0.001) and lower concentrations of free T (3.7 ± 2.2 vs. 7.9 ± 4.1 pmol/L, mean ± SD, P < 0.001); total T did not differ. Total lean mass and leg lean mass were significantly correlated with free, but not total T [r values of 0.29 (P < 0.05) and 0.31 (P < 0.01) for total and leg lean mass, respectively, vs. free T]; arm lean mass was not correlated with either measure of T. Serum E₂ was significantly correlated with SHBG (r = 0.50, P < 0.001) and free T (r = -0.33, P < 0.01). These observations imply that, by reducing the concentration of bioavailable T, oral estrogen therapy may accelerate or augment lean mass loss among postmenopausal women. This conclusion awaits confirmation by longitudinal observation.

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