Sex hormone binding globulin is a carrier protein produced by the liver that plays a critical role in regulating the amount of the unbound steroids, testosterone, dihydrotestosterone (DHT) and estrogen, but mostly testosterone, in the blood. SHBG binds tightly to the hormones testosterone, dihydrotestosterone (DHT), and estradiol. In this bound state, SHBG transports these hormones in the blood as biologically inactive forms. This means that the body is not able to use what is bound to this carrier protein.
In men, elevated SHBG can produce symptoms of low testosterone. This is typically reflected in low free testosterone levels. When checking testosterone levels in men, it is not enough to get just a total testosterone level. Even when total levels are “normal”, the free levels may be low if SHBG is high. It is the free testosterone that is available to the tissue and perform it’s needed action.
In women, SHBG plays an integral role in regulating the levels of bioavailable male sex hormones (androgens) and estrogens circulating throughout the body. SHBG has a higher affinity for the androgens testosterone and DHT and so, in the setting of low SHBG, women may have signs and symptoms related to androgen excess. While it is important to regulate androgens, high SHBG in women can also produce symptoms of low testosterone including, decreased libido, weight gain, decreased strength and decreased energy.
What are some of the causes of SHBG?
- Elevated estradiol levels over normal
- Cirrhosis of the liver
- Birth control pills
- Extreme weight loss as in anorexia nervosa
- Cigarette smoking
- Any estrogen use as plant estrogens (phytoestrogens)
- Increased conversion of testosterone to estrogen
- Certain medications such a Dilantin
- Fibrocystic disease of the breasts
- Any compromise of liver detoxification such as alcohol abuse, certain meds, heavy metals etc. can decrease liver capacity to excrete excess estrogens from the body.
- Stress with elevated cortisol
- Elevated estradiol levels from conversion of testosterone
If you have symptoms of hormone imbalance, it is important to see a healthcare professional who is qualified in interpreting a comprehensive panel of labs in order to develop an individualized plan.