SERUM TESTOSTERONE AND ITS RELATION TO BONE-MINERAL DENSITY AND BODY-COMPOSITION IN NORMAL MALES

OBJECTIVE Bone mineral density (BMD) declines with age in both men and women, predisposing the elderly to osteoporosis and fractures. Althou gh there are extensive data about post-menopausal osteoporosis, there is relatively little information concerning the decrease in BMD with a ge in normal men, particularly the contribution of declining gonadal f unction with age to BMD. In the present study, we investigated the eff ect of age on the pituitary-gonadal axis in normal males and its relat ion to BMD and body composition. SUBJECTS Ninety healthy Thai males in the Bangkok Metropolitan area without a history of smoking or signifi cant alcohol consumption were studied. MEASUREMENTS Serum testosterone (T), free testosterone (FT), LH and FSH were measured by radioimmunoa ssay in fasting blood samples obtained in the morning between 0600 and 1000 h, BMD at anteroposterior L2-L4, lateral L2-L4, femoral neck, fe moral trochanter and Ward's triangle were determined by dual-energy X- ray absorptiometry. RESULTS There were significant declines with age i n BMD at lateral L2-L4 (r = -0.37, P < 0.001), femoral neck (r = -0.49 , P < 0.0001), Ward's triangle (r = -0.54, P < 0.0001) but not at ante roposterior L2-L4 or femoral trochanter, Serum FT (r = -0.56, P < 0.00 01) but not T (r = -0.19, P = 0.07) decreased with age. Serum LH (r = 0.27, P < 0.001) and FSH (r = 0.4, P < 0.0001) increased with age sugg esting a defect in gonadal androgen synthesis or possibly a secretion of bioinactive LH. Serum FT concentrations were significantly correlat ed to lateral L2-L4 (r = 0.27, P < 0.05), femoral neck (r = 0.48, P < 0.0001) and Ward's triangle (r = 0.50, P < 0.0001) BMD. After controll ing for age, declining FT with age was still associated with a decreas e in BMD in femoral neck (P < 0.05) and Ward's triangle (P < 0.05) but not in lateral L2-L4. The proportion of body fat increased with age ( r = 0.3, P < 0.01), Decreased serum T, but not FT, was associated with increased body fat after age was taken into account (P < 0.0001). CON CLUSIONS There is a decline in serum free testosterone together with i ncreases in LH and FSH with age in healthy males. The decrease in seru m free testosterone is partially associated with the age-related decli ne in bone mineral density added to the effect of age at the femoral n eck and Ward's triangle. Testosterone but not free testosterone is ass ociated with age-related increase in body fat.