What Do Your SHBG Levels Mean?
Sex hormone-binding globulin (SHBG) is an important protein produced primarily by the liver but also in smaller quantities by the brain, uterus, placenta, breast and ovaries. Its role is to bind to your sex hormones including testosterone and oestradiol, and transports them around the body, but what can it mean if your levels are high or low? We’ve broken down all you need to know about SHBG levels.
Why do our SHBG levels matter?
The main function of SHBG is to regulate the amount of testosterone and oestradiol available to your body. Only unbound hormones can be used by the body, therefore when SHBG binds to your sex hormones they become inactive. In simple terms, the higher your SHBG, the fewer sex hormones are available to the body, while the lower your SHBG, the more sex hormones are available to the body. SHBG favours testosterone over oestradiol, meaning that it is also important for controlling the balance between these two hormones. The vast majority of testosterone and oestradiol in our bodies is bound to SHBG and other proteins, meaning that only around 2% is available for us to use!
The production of SHBG in our body can also be enhanced and inhibited by various hormones. For instance, SHBG production is known to be blocked by insulin, prolactin and androgens (male sex hormones), whilst high oestrogen levels and thyroxine (T4, a thyroid hormone) are known to increase its production.
What are normal levels of SHBG?: Age, pregnancy and contraceptive use
It is important to remember that ‘normal’ is different for everyone and that our SHBG levels are known to be altered by age, pregnancy and even hormonal contraception. Among menstruators, the ‘normal’ range of SHBG is currently defined as being between 18 and 144 nmol/L.
Your SHBG levels follow a U-shaped trajectory across your lifespan. This means that between the ages of 20 to 60, SHBG levels gradually decline. However, beyond age 60, SHBG starts to rise and continue to do so for the remainder of your life
During pregnancy, SHBG rises gradually until around 24 weeks gestation, after which they remain stable. Oestrogen levels rise in pregnancy which in turn stimulate the production of SHBG in the liver. It has been suggested that this occurs to protect the mother and fetus from androgens during pregnancy.
The combined oral contraceptive has also been shown to increase SHBG. Here, oestrogen in the pill stimulates the liver to produce more SHBG.
Low SHBG: Symptoms and causes
When your SHBG is low, the level of free unbound testosterone can become abnormally high. As a result, low SHBG can cause symptoms that mirror those that arise due to excess testosterone in the body, which can lead to the development of ‘male’ characteristics, and those that result when there is too much oestrogen in the body. These include:
- Excessive body and facial hair
- Hair thinning/ hair loss
- Increased appetite and weight gain
- Irregular or absent periods
- Voice deepening
- Mood changes
- Breast pain
There is no single cause for abnormal SHBG amounts in the body; however, disturbances in insulin and thyroid hormone levels have been shown to directly affect SHBG. Low levels of SHBG can be caused by a number of lifestyle factors, certain medical conditions and genetics. Here are several conditions, as well as other factors, that low SHBG is associated with:
- Obesity: Gaining weight has been shown to have a negative correlation with your SHBG. Simply put, the higher your BMI is, the lower your SHBG levels will be.
- Polycystic Ovarian Syndrome (PCOS): Low SHBG is commonly seen in people with PCOS and may also play a role in the metabolic disturbances that occur with this condition. For this reason, low SHBG is often used to help diagnose PCOS.
- Hypothyroidism: Having an underactive thyroid can cause your SHBG levels to fall. However, with treatment management, which normally involves thyroid medication, these levels will typically return to the normal range.
- Type 2 diabetes: Type 2 diabetes is associated with elevated insulin levels. People with type 2 diabetes may have lower levels of SHBG compared to non-diabetics. However, the links between type 2 diabetes and SHBG are not yet clear and more research is needed to confirm whether type 2 diabetes causes low SHBG or vice versa.
- Hyperprolactinemia: Prolactin inhibits SHBG production and so high levels of prolactin can lead to reduced SHBG. However, SHBG levels typically return to normal with treatment management.
- Acromegaly: Acromegaly is a disorder in which the pituitary gland produces too many growth hormones. Growth hormones have been shown to decrease levels of SHBG in the body. Many women and people assigned female at birth with acromegaly also experience menstrual cycle irregularities.
- Non-alcoholic fatty liver disease (NAFLD): NAFLD is commonly observed in people also suffering from obesity and type 2 diabetes. In both sexes, NAFLD is associated with low levels of SHBG.
- Cushing’s syndrome: Cushing’s syndrome is characterised by abnormally high levels of cortisol. The symptoms of Cushing’s syndrome are similar to the symptoms of PCOS.
Ways to raise low SHBG
If you have low SHBG and wish to raise them, there are a number of lifestyle changes that may help to increase them. These include:
- Exercise: Physical exercise is a great way to raise your SHBG levels. Getting your body moving will not only help you to lose weight but will also help increase your insulin sensitivity, meaning that less insulin is required to regulate your blood sugar levels.
- Weight loss: Regardless of how much you exercise, weight loss alone has been shown to increase SHBG in women.
- Caffeine Intake: A number of studies have reported that caffeinated drinks may increase SHBG. However, a study involving 30 overweight found no differences in SHBG levels with caffeine over an 8 week period. Further clinical studies are required to determine this association.
High SHBG: Symptoms and causes
High SHBG reduces the amount of testosterone and oestrogen that is available to the body for use. Therefore the symptoms of high SHBG levels are equivalent to those that arise due to low testosterone and oestrogen levels.
- Decreased sex drive
- Depression and anxiety
- Reduced muscle and bone mass
- Vaginal dryness
Here are a few conditions that high SHBG levels are associated with:
- Anorexia/ Low BMI: We have seen that obesity can lead to low levels of SHBG and that the levels can be raised with weight. However, it has also been shown that a very low BMI can lead to SHBG levels becoming higher than the normal range.
- Type 1 Diabetes: SHBG production is blocked by insulin. In type 1 diabetes the pancreas no longer makes insulin which can lead to higher levels of SHBG.
- Hyperthyroidism: Too many thyroid hormones in the body can lead to increased levels of SHBG. Like with hypothyroidism, SHBG levels have been shown to normalise following treatment for hyperthyroidism.
- Alcohol Consumption: Drinking alcohol may increase SHBG. A study of over menstruators showed that consuming more than 2.5 units a day was associated with significantly raised SHBG levels.
Ways to lower high SHBG
- Dietary Recommendations: Following a high-fat, low fibre diet may help decrease levels of SHBG. One study involving 48 premenopausal women showed that maintaining a high-fat, low diet decreased SHBG. However, more clinical studies are required to confirm this association.
If you are experiencing any of the mentioned symptoms or would like to get an insight into your fertility and hormone health, we have the solution for you. With our tailored at-home testing, we can help give you an insight into your ovarian reserve, your cycle, your hormones and highlight any red flags. If you need help with symptom management, our team of expert clinicians are here to help you create an actionable plan for your future.