Sex hormone-binding globulin (SHBG) is a protein that binds certain hormones. When SHBG is low, more of these hormones are available, which can result in excess testosterone and estrogen in males and females.
Sex hormone-binding globulin (SHBG) is a protein produced mainly in the liver. It binds certain hormones, including:
SHBG carries these hormones throughout your bloodstream. Hormones in this bound state aren’t available for your cells to use. It’s your body’s way of regulating hormone levels.
Generally speaking, when your SHBG levels are low, your body has more unbound sex hormones available for use. When your SHBG levels are high, your body has fewer free sex hormones at its disposal.
Normal SHBG levels vary according to gender and age. But many other factors can influence SHBG levels and cause them to be abnormally low or high.
Read on to learn more about SHBG levels and explore the reasons you might need to be tested.
The normal ranges for SHBG concentrations in adults are:
- Males: 10 to 57 nanomoles per liter (nmol/L)
- Females (nonpregnant): 18 to 144 nmol/L
Men typically have lower SHBG levels than women. However, a man’s SHBG level will usually increase with age as his testosterone levels drop.
Pregnancy usually raises SHBG levels. They typically return to normal after childbirth.
Please keep in mind that the normal range values may vary from lab to lab depending on where you have this test performed.
If your SHBG levels are low, there are potentially more free sex hormones for your body to use.
In men, excessive free testosterone can result in:
Too much estrogen in men can cause:
In women, too much testosterone can result in:
Too much estrogen can lead to:
- irregular periods
- mood swings
- breast tenderness
The following makes it more likely for a person to develop low SHBG levels:
- insulin resistance, which occurs in type 2 diabetes
- Cushing disease
- nonalcoholic fatty liver disease
- acromegaly (too much growth hormone in adults)
- androgen steroid use
In males and females, levels of SHBG are higher before puberty than in adulthood, but after puberty begins, a person’s SHBG level then decreases. They become stable in adulthood.
As a man ages, SHBG levels rise. This may be related to higher levels of testosterone production during puberty and lower levels of testosterone production as a man ages.
In women, it’s less clear how aging and menopause affect SHBG levels.
Women with polycystic ovary syndrome (PCOS) may have low SHBG levels and tend to have insulin resistance, obesity, and excess androgen production.
Research also suggests that low SHBG levels in adult women may be a marker for predicting the development of type 2 diabetes. Low SHBG levels also go along with being overweight.
SHBG tests usually aren’t part of a routine checkup. Your doctor might order it:
- if you have symptoms of abnormal SHBG levels, hypogonadism, or any other type androgen deficiency
- if total testosterone test results don’t provide a complete picture
- to learn more about why your testosterone or estrogen levels are excessively low or high
In men, the test can be used to help determine the cause of:
In women, the test can help determine the cause of:
For the test, a blood sample is drawn from a vein in your arm. The test measures the concentration of SHBG in your blood. The blood sample is then sent to a laboratory for analysis, after which your doctor receives the results.
There’s no preparation needed for this test. But certain things can affect the results. Tell your doctor if you:
- take opiates, central nervous system medications, or any other drugs or medications
- take vitamins, herbs, or other dietary supplements
- have an eating disorder or exercise excessively
Treatment of a low SHBG depends on the cause. Any underlying conditions will have to be addressed.
Your doctor will explain the results of your SHBG test and what your treatment options are, if treatment to address this is necessary. You should always follow your doctor’s recommendations.
Research has found that the following may increase SHBG levels:
Get regular exercise
A large-scale trial in a select population found evidence that SHBG can be increased through exercise. The study looked at women who were postmenopausal, mostly overweight, and previously sedentary. The year-long exercise intervention included an average of 178 minutes of aerobic exercise per week.
Research on women over age 60 indicates that having two or more cups of regular caffeinated coffee a day is associated with higher SHBG concentrations.
Take certain oral contraceptives
Increase fiber and decrease sugar in your diet
A 2000 study involving men between the ages of 40 and 70 found that fiber intake increased SHBG levels, while protein intake lowered levels. However, researchers of this study note their results differ from findings in previous studies.
Other research shows that when children who are obese lose weight, SHBG levels can rise significantly.
Take certain supplements
Many herbal and dietary supplements claim to help lower SHBG levels in order to boost testosterone.
While some may have merit, it’s difficult to know for sure. Supplements aren’t regulated by the Food and Drug Administration (FDA), so manufacturers are free to make claims that may not be true.
Some supplements contain ingredients that can cause unwanted side effects and interact with prescription medications or aggravate underlying health conditions.
You should always consult with your doctor before adding a new supplement to your routine. They can review the product and discuss your risk for adverse effects.
Your SHBG level will change throughout your lifetime.
If your SHBG concentration is outside the normal range for your health profile, your doctor will review your symptoms to determine the underlying cause.
In some cases, a few lifestyle changes may be all you need to get your SHBG levels back on track. In others, a combination of prescription medication and other clinical therapies may be needed.
If no underlying condition is found, your doctor will inform you what steps, if any, to take next.