What Do Your SHBG Levels Mean?-image

What Do Your SHBG Levels Mean?

Sex hormone-binding globulin (SHBG) is an important protein involved in the regulation of our sex hormones. Just like our menstrual cycle, thyroid and fertility hormones, our SHBG levels can affect our reproductive health—including our ability to conceive. 

So what is a good, or ‘normal’ range for our SHBG levels? And how do we know when ours might be too high or too low? 

We’ve broken down all you need to know about SHBG levels, including what they mean, why they matter and what to do if you suspect yours might be out of range.

  1. What is SHBG?
  2. Why do SHBG levels matter?
  3. What are normal levels of SHBG?
  4. Low SHBG
  5. High SHBG
  6. SHBG hormone tests

What is SHBG?

SHBG is an important protein that regulates the amount of testosterone and oestrogen available in the body. Affecting both those assigned-female and male-at-birth, SHBG is made primarily in the liver, but also in smaller amounts in the testes, brain, uterus, placenta, breasts and ovaries. 

SHBG controls the level of testosterone and oestrogen in the bloodstream by ‘binding’ to these hormones—which renders them inactive. This is because only unbound hormones can be used by the body. 

The vast majority of testosterone and oestrogen in our bodies is bound to SHBG and other proteins, with only around 2% available to be used. SHBG also controls the balance between testosterone and oestrogen, which is also important for the healthy functioning of our menstrual cycles.

Why do SHBG levels matter?

Because SHBG levels regulate the amount of testosterone and oestrogen available to be used by the body, if our SHBG levels are too high or low, this will have a knock on effect on our levels of both of these sex hormones. 

If our SHBG levels are higher, we’ll have less testosterone or oestrogen available. If our SHBG levels are lower, we’ll have more testosterone and oestrogen available. 

Both of these sex hormones have important roles in the regulation of the menstrual cycle, ovulation, libido, energy levels and our mental health.

What are normal levels of SHBG?

Our SHBG levels follow a U-shaped trajectory across our lifetimes—meaning that they gradually decline between ages 20 to 60, before rising post 60 for the rest of our lives.

However, it’s important to remember that ‘normal’ is different for everyone and there are times when our SHBG levels can deviate.

For most people of menstrual age (13-45), a ‘normal’ range for SHBG is between 18 and 144 nmol/L.

But there are times where this differs. SHBG increases during the first 24 weeks of pregnancy and has been found to increase when taking combined oral contraceptive pill.Our SHBG level can also be enhanced or inhibited by other hormones, their levels in our bloodstream and their knock-on effects. Higher levels of insulin, prolactin and androgens (male sex hormones) have been found to block SHBG production, whereas high oestrogen and thyroxine (T4), which is one of our main thyroid hormones, have been found to increase it.

Low SHBG

When our SHBG levels are low, our levels of free unbound testosterone and oestrogen can become abnormally high. Let’s take a look at some of the symptoms, causes and what can be done to help.

Symptoms of low SHBG

These symptoms can often mirror those of excess testosterone including:

  • Excessive body and facial hair (hirsutism)
  • Acne
  • Increased appetite and weight gain
  • Irregular or absent periods
  • Voice deepening

Or excess oestrogen

  • Hair thinning/hair loss
  • Mood changes
  • Breast pain

Causes of low SHBG

There is no single cause for abnormal SHBG levels, although as we mentioned previously, increases in insulin, prolactin and androgens have been found to block SHBG production which could be a factor for those with low SHBG levels. 

Low SHBG can also 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 has been found to be associated with:

  • Obesity:
    Gaining weight has been shown to have a negative correlation with our 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. 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 their 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.

How to raise low SHBG

If you have low SHBG there are a number of lifestyle changes that may help to increase your levels. These include:

  • Exercise:
    Getting our bodies moving helps increase our insulin sensitivity (how our bodies regulate insulin) which has been shown to improve SHBG levels.
  • Low sugar, high fibre diet:
    Reducing our sugar intake and increasing fibre in our diets has also been found to improve SHBG levels.
  • Weight loss:
    Weight loss alone has been shown to increase SHBG in women. Only consider this option if you have an elevated BMI.
  • Caffeine Intake:
    A number of studies have reported that caffeinated drinks may increase SHBG but further clinical studies are required to determine this association.

High SHBG 

On the flip side, when our SHBG levels are too high, our unbound testosterone and oestrogen can become abnormally low. Here are some symptoms, causes and what can be done to reduce high levels of SHBG.

High SHBG

These symptoms can often mirror those of low testosterone including: 

  • Decreased sex drive
  • Depression and anxiety
  • Reduced muscle and bone mass
  • Vaginal dryness

Or low oestrogen:

  • Depression and anxiety
  • Reduced muscle and bone mass
  • Vaginal dryness

Causes of high SHBG

Again, there is no single cause for abnormal SHBG levels, although as we mentioned previously, increases in oestrogen and thyroxine (T4) have been found to increase SHBG production, which could be a factor for those with high SHBG levels.

There are also a number of conditions associated with high SHBG which include:

  • Anorexia/ Low BMI:
    We’ve seen that a high BMI or obesity can lead to low levels of SHBG and the same is true for a very low BMI leading to high SHBG levels too. 
  • Type 1 Diabetes:
    In type 1 diabetes the pancreas no longer makes insulin, which can lead to higher levels of SHBG.
  • Hyperthyroidism:
    Too many thyroid hormones (like T4) 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. One study showed that consuming more than 2.5 units a day was associated with significantly raised SHBG levels.

How to lower SHBG

Dietary changes are the most effective way to lower SHBG levels. Decreasing alcohol consumption, gaining weight if you have a low BHM and 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.

Other possible causes such as type 1 diabetes and an overactive thyroid will need further investigation and will require medication specific to these conditions.

SHBG tests

Ultimately, if you suspect you may have abnormal levels of SHBG, the only way to definitively get a diagnosis is via a blood test. Because symptoms of abnormal SHBG levels can mimic those of high or low oestrogen and testosterone, your SHBG levels should be tested in tandem with your T4 and Oestradiol (E2), in addition to your thyroxine (T4) levels if you suspect you have high SHBG. You can test all of these hormones and more, with a Hertility at-home Hormone and Fertility Test.

Key Takeaways

  • Sex Hormone Binding Globulin (SHBG) is an important protein involved in the regulation of our sex hormones in both men and women.
  • It is made in the liver and regulates the amount of testosterone and oestrogen available in the body
  • Normal levels of SHBG will vary from person to person but generally they gradually decline between ages 20 to 60, before rising post 60 for the rest of our lives
  • When our SHBG levels are low, our levels of free unbound testosterone and oestrogen can become abnormally high, resulting in symptoms associated with high oestrogen and testosterone
  • When our SHBG levels are high, our levels of free unbound testosterone and oestrogen can become abnormally low, resulting in symptoms associated with low oestrogen and testosterone
  • You can measure your SHBG levels with an at-home Hormone and Fertility Test.

 

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Zoya Ali BSc, MSc

Zoya Ali BSc, MSc

Zoya is a scientific researcher with a Bachelor's degree in Biotechnology and a Masters in Prenatal Genetics & Foetal Medicine from University College London. Her research interests are reproductive genetics, fertility preservation, gynaecological health conditions and sexual health.

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