Sex Hormone-Binding Globulin (SHBG) is a protein produced by the liver. Its primary function is to bind to sex hormones, mainly testosterone and estrogen, and transport them through the bloodstream. By doing so, SHBG regulates the amount of active hormones available for your body’s tissues to use. This article explores the function of SHBG, the factors that can elevate its levels, and the resulting consequences.
The Function of SHBG in Hormone Regulation
SHBG regulates sex hormone availability by binding to hormones like testosterone, dihydrotestosterone (DHT), and estradiol. This binding creates two categories of hormones in the bloodstream: “bound” and “free.” When a hormone is bound to SHBG, it is biologically inactive and cannot be used by the body’s tissues.
Only the “free” hormones, those not attached to SHBG, are bioavailable and can influence physiological processes. Think of SHBG as a transport vehicle; hormones that are “passengers” are in storage and cannot interact with cell receptors. For this reason, measuring only “total” testosterone can be misleading if SHBG levels are abnormal.
A high SHBG level means more hormones are bound and inactive, leading to a lower concentration of free, usable hormones. Conversely, a low SHBG level results in more free hormones circulating in the bloodstream. The concentration of SHBG, therefore, directly modulates the impact of sex hormones on functions ranging from reproduction to muscle mass and mood.
Factors That Increase SHBG Levels
Several factors, from medical conditions to lifestyle choices, can increase SHBG production. Since the liver is the main site of SHBG synthesis, its health is directly linked to SHBG levels. Common causes of elevated SHBG include:
- Liver conditions such as cirrhosis and hepatitis.
- An overactive thyroid gland (hyperthyroidism), which stimulates the liver to produce more SHBG.
- Significant weight loss, very low-calorie or low-fat diets, and conditions like anorexia nervosa.
- Excessive exercise, which can influence hormones that affect SHBG production.
- Certain medications, including oral contraceptives containing estrogen and some antiepileptic drugs.
- The natural aging process, which leads to a gradual increase in SHBG in both men and women.
Consequences of High SHBG
Elevated SHBG reduces the amount of free sex hormones, which can cause symptoms of hormone deficiency even when total hormone levels appear normal. These effects manifest differently in men and women due to the distinct roles testosterone and estrogen play in their bodies.
In men, high SHBG lowers the amount of free testosterone. This can lead to symptoms characteristic of low testosterone, including decreased sex drive (libido), erectile dysfunction, fatigue, and reduced muscle mass and bone density. Mood changes, such as depression or difficulty with concentration, can also occur.
For women, high SHBG reduces both free testosterone and free estrogen. Testosterone is important for female health, contributing to libido, energy, and bone strength. Consequently, women with high SHBG may experience low libido, fatigue, and an irregular menstrual cycle. The reduction in bioavailable estrogen can also affect bone density.
Approaches to Influence SHBG Levels
Managing high SHBG involves identifying and addressing the underlying cause with a healthcare professional. Treating medical issues like hyperthyroidism or liver disease is the most direct way to normalize SHBG levels. A medical evaluation with blood tests for thyroid and liver function is the first step.
Dietary adjustments can also influence SHBG. Increasing protein and healthy fat intake may help lower it, as very low-fat diets tend to raise SHBG. A diet rich in whole foods is advisable, as some research suggests micronutrients like boron, magnesium, and zinc may play a role.
Since very low body weight is linked to high SHBG, achieving and maintaining a healthy weight can help restore balance. Always approach dietary or lifestyle changes under medical guidance. Self-treating with supplements or extreme diets can be unsafe without a proper diagnosis of the root cause.