Measures of bioavailable serum testosterone and estradiol and their relationships with muscle strength, bone density, and body composition in elderly men

In the present cross-sectional study of 403 independently living elderly men, we tested the hypothesis that the decreases in bone mass, body composition, and muscle strength with age are related to the fall in circulating endogenous testosterone (T) and estrogen concentrations. We compared various measures of the level of bioactive androgen and estrogen to which tissues are exposed. After exclusion of subjects with severe mobility problems and signs of dementia, 403 healthy men (age, 73-94 yr) were randomly selected from a population-based sample. Total T (TT), free T (FT), estrone (E-1), estradiol (E-2), and sex hormone-binding globulin (SHBG) were determined by RIA. Levels of non-SHBG-bound T (non-SHBG-T), FT (calc-FT), the TT/SHBG ratio, non-SHBG-bound E-2, and free E-2 were calculated. Physical characteristics of aging included muscle strength measured using dynamometry, total body bone mineral density (BMD), hip BMD, and body composition, including lean mass and fat mass, measured by dual-energy x-ray absorptiometry. In this population of healthy elderly men, calc-FT, non-SHBG-T, E-1, and E-2 (total, free, and non-SHBG bound) decreased significantly with age. T (total and non-SHBG-T) was positively related with,muscle strength and total body BMD (for non-SHBG-T, respectively, beta = 1.93 +/- 0.52, P < 0.001 and beta = 0.011 +/- 0.002 P < 0.001). An inverse association existed between T and fat mass (beta = -0.53 +/- 0.15, P < 0.001). Non-SHBG-T and calc-FT were more strongly related to muscle strength, BMD, and fat mass than TT and were also significantly related to hip BMD. E-1 and E-2 were both positively, independently associated with BMD (for E-2, beta = 0.21 +/- 0.08, P < 0.01). Non-SHBG bound E-2 was slightly strongly related to BMD than total E-2. The positive relation between T and BMD was independent off,. E-1 and E-2 were not related with muscle strength or body composition. In summary, bioavailable T, E-1, total E-2, and bioavailable E-2 all decrease with age in healthy old men. In this cross-sectional study in healthy elderly men, non-SHBG-bound T seems to be the best parameter for serum levels of bioactive T, which seems to play a direct role in the various physiological changes that occur during aging. A positive relation with muscle strength and BMD and a negative relation with fat mass was found. In addition, both serum E-1 and E-2 seem to play a role in the age-related bone loss in elderly men, although the cross-sectional nature of the study precludes a definitive conclusion. Non-SHBG-bound E-2 seems to be the best parameter of serum bioactive E-2 in describing its positive relation with BMD.