Sex hormone-binding globulin in osteoporosis.

Sex hormone-binding globulin (SHBG) is a plasma glycoprotein that binds with high affinity to sex steroids, most notably 5alpha-dihydrotestosterone, testosterone, and 17beta-estradiol, thereby regulating their bioavailability and access to target cells. SHBG modulates the sex-steroid signaling system by binding to a specific membrane receptor (SHBG-R). Plasma SHBG levels vary in health and disease due to the effects of multiple regulation factors (age, body weight, sex steroids, insulin, and others).