SHBG

Sex hormone-binding globulin (SHBG) is a special protein made by your liver that acts like a hormone “gatekeeper.” Its main job is to transport and control the availability of sex hormones, particularly testosterone and estrogen, so that only the right amount is active in your tissues. Most circulating sex hormones in your blood are bound to SHBG or another carrier protein called albumin, leaving only a small fraction “free” and able to interact with cells. This free fraction is what drives many biological effects.

SHBG levels are influenced by several factors:

• Hormone levels: Estrogen tends to raise SHBG, while testosterone and insulin lower it.
• Thyroid function: Higher thyroid hormone can increase SHBG production.
• Liver fat and inflammation: Fat accumulation in the liver (a key feature of non-alcoholic fatty liver disease, NAFLD) and inflammatory signals called cytokines can reduce SHBG production, even if body weight is unchanged.
• Nutrition and metabolic health: Low-calorie diets and certain nutrients can increase SHBG, whereas high insulin levels, common in insulin resistance, tend to suppress it.

Low SHBG is more than just a laboratory finding; it is consistently linked to insulin resistance, type 2 diabetes, NAFLD, and metabolic syndrome. Large observational and genetic studies suggest that low SHBG is not only a marker but may also play a role in causing these conditions, particularly in women. People with low SHBG often have higher liver fat production, which can accelerate NAFLD progression.

SHBG also connects to cardiovascular health. Higher SHBG levels are generally linked to better cholesterol profiles and lower resting heart rates. However, very high SHBG, particularly in older adults, can be associated with lower bone density and frailty, especially in women living with HIV or hepatitis C.

SHBG also connects to cardiovascular health. Higher SHBG levels are generally linked to better cholesterol profiles and lower resting heart rates. However, very high SHBG, particularly in older adults, can be associated with lower bone density and frailty, especially in women living with HIV or hepatitis C.

In reproductive and endocrine health, low SHBG is often seen in polycystic ovary syndrome (PCOS), where it can worsen symptoms by increasing free testosterone. Certain genetic variations in the SHBG gene may predispose to lower levels and higher PCOS risk. In men, low SHBG can indicate metabolic problems, liver disease, or excess body fat, and it affects the interpretation of testosterone levels.

Importantly, SHBG can be altered by medications. For example, estrogen-containing birth control pills raise SHBG, while some anabolic steroids lower it.

Because SHBG reflects both hormone balance and liver-metabolic function, it is emerging as a valuable biomarker. It can help identify hidden insulin resistance, track NAFLD progression or regression, and improve the accuracy of hormone testing. Some researchers are exploring whether therapies that raise SHBG could help prevent or treat metabolic diseases and PCOS.