Sex Hormone Binding Globulin, or SHBG, is a protein produced by the liver that plays a vital role in regulating your body's sex hormones, particularly testosterone, dihydrotestosterone (DHT) and oestrogen. SHBG binds to these hormones and controls how much hormone is available for your body to use. We often measure SHBG to check for hormone imbalances that can cause issues such as polycystic ovarian syndrome (PCOS), irregular periods and infertility in women or low libido and problems with erections in men.
Most (about 98%) testosterone and oestrogen circulates in your bloodstream “bound” to two proteins - albumin and sex hormone binding globulin. Only a small fraction (about 2%) is unbound or “free”. However, it’s this free hormone that’s actually “bioavailable” to have an effect on your cells. So, you can think of SHBG as a “mop” soaking up testosterone and oestrogen and preventing them from having an effect.
In this way, SHBG acts as a sex hormone regulator, releasing more when your body needs them and locking them away when their levels are too high. For instance, during puberty in males, less SHBG is produced because the body needs more free testosterone to stimulate development of male characteristics.
Doctors often check SHBG levels when investigating hormone-related symptoms.
For men, we would check SHBG when investigating signs of low testosterone such as low sex drive, mood changes, erectile dysfunction and loss of muscle mass. If the SHBG level is high, the level of free testosterone available to your body may be low. This can cause a problem even if your total testosterone level is ok.
In women, SHBG levels are important when investigating PCOS, irregular periods and fertility problems. In PCOS, we tend to see lower SHBG levels and high levels of testosterone.
The levels of SHBG depend on a person’s sex, age and the presence of certain health conditions. Therefore, the normal ranges for SHBG levels differ across age groups between men and women, as shown in the table below.
<50 years | ≥ 50 years | |
Female | 27 - 146 nmol/L | 22 - 142 nmol/L |
Male | 15 - 55 nmol/L | 19 - 83 nmo/L |
SHBG levels also increase 5 to 10 fold in pregnancy. This may be to protect the mother from the effects of androgens produced by the foetus.
Low SHBG levels usually mean that there are higher levels of bioavailable androgens and oestrogens. The androgenic effects are most pronounced because SHBG binds more easily to androgens than oestrogens.
If SHBG levels are low in women, they might experience symptoms related to higher levels of bioavailable testosterone such as:
Low SHBG levels in men will result in higher levels of free testosterone. Many men wouldn’t notice any symptoms as they have high levels of testosterone to begin with. However, if free testosterone levels got very high, they might notice:
Your genes play a major role in your SHBG level and account for about 50% of the variation we see between individuals1, 2. However, there are some non-genetic factors that can result in a low SHBG:
In general, the best way to increase SHBG level is to treat the cause of low SHBG if that’s known. Otherwise, some other factors that can increase your SHBG levels are:
As we’ve seen above, a low SHBG level is associated with obesity, metabolic syndrome and insulin resistance. It shouldn’t come as a surprise then that in general, higher SHBG levels are associated with a lower risk of diabetes and heart disease10, 11.
However, it’s still possible for SHBG levels to be too high, resulting in low levels of bioavailable testosterone and oestrogen.
High SHBG levels in women would be expected to lower bioavailable testosterone and oestrogen, causing symptoms such as:
In men, a high SHBG level would result in a low level of free testosterone, causing symptoms of low testosterone:
The common causes of high sex hormone binding globulin include:
If the cause of high SHBG is known, it’s best to address this first. However, one lifestyle factor that has been shown to lower SHBG levels is increasing protein intake, particularly in older men16. High protein intake may therefore increase bioavailable testosterone levels which is beneficial for muscle mass and metabolic health.
In most cases, you don’t need any special preparation for the SHBG test. However, high-dose biotin supplementation can interfere with the assay used to measure SHBG levels. This can cause falsely low results. It’s best to stop high-dose biotin supplements for a few days before checking your SHBG level.
We don’t tend to measure SHBG on its own, rather we would test it alongside other hormones such as testosterone and oestradiol. We would then put together the whole picture to determine what to do next if you have abnormal SHBG levels.
For example, we might suggest further testing to look at the levels of pituitary hormones, LH and FSH, which control testicular and ovarian hormone production. It might also be necessary to check your thyroid and liver function as these can influence SHBG production.
A lot of the time, an abnormal SHBG level is a sign that other areas of your health could be improved, such as your nutrition and exercise regimen.
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