Association between endogenous hormones and sex hormone-binding globulin and bone turnover in older women: study of osteoporotic fractures

Estrogen therapy decreases bone remodeling, but the association between endogenous estradiol (E2), estrone (E1), testosterone (T), and bone turnover in older women is not clear. To test the association of serum E2, E1, free T, and sex hormone-binding globulin (SHBG) with bone turnover, we analyzed cross-sectional relationships among E2, E1, T, SHBG, and biochemical markers of bone turnover serum osteocalcin [OC], serum bone-specific alkaline phosphatase [bAP], and serum breakdown products of C telopeptide of type I collagen [CTx] in 704 women enrolled in the Study of Osteoporotic Fractures. Women with lower estradiol levels tended to have higher levels of bone turnover, but the association was weak (R2 = 0.01 for the association E2-OC, p = 0.03; and R2 = 0.024 for E2-CTx, p = 0.001). Relationships between SHBG and turnover were also weak (R2 for the association SHBG-OC was 0.07, p< 0.001, and 0.03 for SHBG-sCTx, p = 0.03), or not significant (R2< 0.01 for the association SHBG-bAP). Associations of E1 and T with these markers were of the same magnitude. These results were not modified after adjustment for age, weight, and smoking status. We conclude that older women with low endogenous hormones have somewhat higher bone turnover, but these associations are weak. Bone turnover is determined mainly by factors other than endogenous concentrations of sex hormones.