SHGB (Sex hormone binding globulin)

Sex hormone binding globulin (SHBG) is a reproductive hormone produced by the liver that plays a vital role in both male and female reproductive health. It binds and carries sex hormones, particularly testosterone, to the tissues and organs where they are needed. By doing so, SHBG regulates the proportion of sex hormones that are available to be used by your body.

Different diseases can cause SHBG levels to rise too high, or fall too low. When this happens, there may be too large or too small a fraction of sex hormones that can have an effect on the body. This makes itself known through a variety of symptoms.

Read on to learn about SHBG and how it is tested, how it plays a role in regulating the body’s hormonal economy, what happens if its levels become unbalanced, and how this can be treated.

Sex hormone binding globulin, or SHBG, is an important reproductive hormone in both men and women. While SHBG doesn’t directly act on tissues and organs like other hormones do, it plays an equally significant role by acting as a carrier for sex hormones. Hormones bind to SHBG and then are released, depending on the needs of the body. The hormones that bind to SHBG are: 1 2

• Dihydrotestosterone (DHT)
• Testosterone
• Estradiol

SHBG is produced by hepatocytes, which are a type of liver cell involved in metabolism. 1

Generally, hormones in the human body exist in either a free or a protein-bound (bound) state. Free hormones are biologically active, and can have a direct influence on their target tissues and organs. Meanwhile, bound hormones are biologically inactive, and cannot act on their targets until they are released from the bound state. SHBG binds certain sex hormones, and transports them to different areas of the body. 3

The proportion of sex hormones circulating in the bound state depends on the SHBG hormone levels in your blood. If SHBG levels are high, a larger fraction of sex hormones will bind to it, so a smaller fraction will be free and biologically active. If SHBG levels are low, a smaller proportion of sex hormones in the circulation are protein-bound, so a larger proportion circulates in the free state. 4

Abnormally high or low SHBG levels can cause problems because they influence the proportion of sex hormones that are biologically active. Such imbalances can disturb the delicate hormonal ecosystems that our bodies have in place.

If your SHBG levels are found to be high, it means that your liver cells are overproducing the hormone, and there is too much of it circulating in your blood. High SHBG levels can result from healthy response mechanisms in your body seeking to correct imbalances in your hormone levels. However, high SHBG can also arise abnormally, such as when your liver cells are not functioning properly. 1 2

There are many causes of high SHBG, including: 2

• Hyperthyroidism
• Anorexia
• Pregnancy
• Low growth hormone levels
• Low testosterone levels
• Liver disease

When you have high SHBG, a higher proportion of your sex hormones will bind to it and be biologically inactive.

In the long term, SHBG on the high end of the normal range can have a protective effect on the heart, and research has also shown that it may decrease one’s risk of prostate cancer. However, it is not as desirable in the elderly, as it has been linked to weakened bones. 4

If your SHBG is low, it means that there is not enough of it circulating in your blood. In people with low SHBG, a higher proportion of sex hormones circulate in the free state, meaning that they are available for the body to use. Therefore, people with low SHBG often experience symptoms of high testosterone. 5

Causes of low SHBG include: 2

• Obesity
• Hypothyroidism
• High growth hormone levels
• High testosterone levels
• High insulin levels (hyperinsulinemia)
• Genetic causes

Because SHBG primarily binds testosterone, symptoms of abnormally high or low testosterone levels in both men and women may warrant an SHBG test. This test requires a small sample of blood to be taken. Such a sample can be drawn from a vein in your arm in a healthcare setting, or taken independently at home and sent to a lab for analysis. 2

Symptoms such as erectile dysfunction, depression, weight gain, muscle loss, or hair loss are common in men with low testosterone levels. Meanwhile, men with abnormally high testosterone may experience acne, high blood pressure, heart problems, hair loss, or infertility.

In women, low testosterone can manifest as irregular periods, depression, or reduced libido, while high testosterone is often an effect of polycystic ovary syndrome (PCOS) and can cause acne, weight gain, irregular periods, depression, or excessive hair growth on the face (hirsutism). 1 6

In women with symptoms of high testosterone, total testosterone is divided by SHBG and multiplied by 100 to calculate the free androgen index (FAI). This is useful for determining how much testosterone is available for use by the body. 2 7

Many different diseases and conditions can cause high or low SHBG, so there is no one-size-fits-all cure for imbalances in its levels. If your SHBG levels fall outside of the normal range, your doctor will run further investigations to determine if this is the result of a medical condition. Your SHBG levels should improve as the medical condition responsible for their abnormal levels is treated.

Q: What causes high SHBG in males?
A: An overactive thyroid (hyperthyroidism), anorexia, low growth hormone levels, low testosterone levels, and liver disease can all cause high SHBG in males.

Q: How to lower SHBG?
A: There are many conditions and diseases that cause elevated SHBG. High SHBG treatment involves treating the underlying cause of the imbalance.

Q: How to lower SHBG in females?
A: A recent study demonstrated that eating foods with more sugar, a higher glycemic index (GI), or higher glycemic load (GL) can result in lower SHBG levels in postmenopausal women.

Q: How to increase SHBG?
A: Your SHBG levels should return to their optimal range when any condition responsible for their low levels is treated. Research has also demonstrated that regular aerobic exercise can help raise SHBG levels.

Q: Is there a link between high SHBG and hair loss?
A: There is research to suggest that having low rather than high SHBG levels may result in hair loss.

Q: When to see a doctor?
A: If you are experiencing symptoms of abnormally high or low testosterone, it may be worth consulting a doctor. An SHBG test may or may not be offered as a first-line investigation.