Circulating sex steroids, sex hormone-binding globulin, and longitudinal changes in forearm bone mineral density in postmenopausal women and men: the Tromsø study.

Bone loss during advancing age in women and men is partly the result of sex steroid deficiency. As the contribution of circulating sex steroids and sex hormone-binding globulin (SHBG) to bone loss remains uncertain, we sought to determine whether levels of sex steroids or SHBG predict change in bone mineral density (BMD) in women and men. A population-based study in the city of Tromsø of 6.5 years' duration (range 5.4-7.4) included 927 postmenopausal women aged 37-80 years and 894 men aged 25-80 years. Total estradiol and testosterone, calculated free levels, and SHBG were measured at baseline, and BMD change at the distal forearm was determined using BMD measurements in 1994-1995 and 2001. Bone loss was detected in postmenopausal women and men. Free estradiol and SHBG predicted age-adjusted bone loss in postmenopausal women, but only free estradiol was associated after further adjustment for body mass index and smoking in mixed models (P < 0.05). After same adjustment, only SHBG persisted as a significant independent predictor of bone loss in men (P < 0.001). However, only 1% of the variance in bone loss was accounted for by these measurements. We therefore conclude that the relations between sex steroids and bone loss are weak and measurements of sex steroids are unlikely to assist in clinical decision making.