What is sex hormone binding globulin?

Sex Hormone Binding Globulin (SHBG) is a protein present in both men and women that binds to sex steroid hormones, such as testosterone and estrogen, preventing them from being in their free or active form. This binding can regulate the levels of these hormones that are active in the body, impacting various body functions. Importantly, SHBG can be influenced by factors such as caffeine intake and nutritional status. For instance, caffeine has been shown to increase SHBG, which might slightly reduce levels of free testosterone and estradiol, although such effects are generally minor at moderate caffeine consumptions. Additionally, factors like insulin levels, affected by carbohydrate intake, can decrease SHBG, which would increase free testosterone levels 1 2.