Sex Hormone Binding Globulin

A protein that binds and inactivates sex hormones.

What it is

Sex Hormone Binding Globulin, or SHBG for short, is a special type of protein made by your liver. Its main job is to travel around in your bloodstream and attach itself to certain sex hormones, primarily testosterone and oestrogen. Think of it like a taxi service for these hormones – it picks them up and carries them around the body.

When SHBG binds to a hormone, it essentially makes that hormone inactive. This means the hormone can't easily reach the cells in your body where it might have an effect. Only the hormones that are not bound to SHBG are considered "free" or "bioavailable," meaning they are able to do their work. The level of SHBG in your blood can therefore influence how much active testosterone or oestrogen is circulating.

Why it matters

The amount of SHBG in your blood is important because it directly affects the levels of active testosterone and oestrogen available to your body's tissues.

In men, testosterone is crucial for many functions, including building muscle, maintaining bone density, sperm production, and sex drive. If SHBG levels are too high, it can bind up too much testosterone, leaving less free testosterone available. This can potentially lead to symptoms associated with low testosterone. Conversely, if SHBG levels are too low, more testosterone might be free and active, which could also have implications.

In women, oestrogen plays a key role in reproductive health, bone health, and mood. While SHBG binds to oestrogen, its impact on oestrogen activity is generally less pronounced than its effect on testosterone in men. However, imbalances in SHBG can still contribute to hormonal disruptions.

SHBG levels can also be an indicator of underlying health conditions, such as insulin resistance, type 2 diabetes, and liver problems.

What can cause it to be high or low

Several factors can influence your SHBG levels, leading to them being higher or lower than the typical range (which for adults is generally between 18.3–54.1 nmol/l, though this can vary slightly between labs).

Factors that may be associated with higher SHBG levels include:

• Certain medications: Some medications, like certain types of hormone therapy or anti-epileptic drugs, can increase SHBG.
• Hyperthyroidism: An overactive thyroid gland can sometimes lead to higher SHBG.
• Liver health: A healthy liver is needed to produce SHBG, but certain liver conditions might paradoxically lead to higher levels.
• Pregnancy: SHBG levels naturally rise during pregnancy.
• Oestrogen therapy: Taking oestrogen, for example, as part of hormone replacement therapy (HRT), can increase SHBG.

Factors that may be associated with lower SHBG levels include:

• Obesity: Being overweight or obese is strongly linked with lower SHBG levels.
• Insulin resistance and Type 2 Diabetes: High insulin levels, often seen in these conditions, can suppress SHBG production.
• Hypothyroidism: An underactive thyroid gland can sometimes be associated with lower SHBG.
• Low testosterone (in men): While it might seem counterintuitive, very low testosterone levels can sometimes be associated with lower SHBG.
• Certain medications: Some medications, including anabolic steroids and progestins, can lower SHBG.
• Polycystic Ovary Syndrome (PCOS): This condition in women is often associated with insulin resistance and lower SHBG levels.
• Ageing: SHBG levels may naturally decline slightly with age.

Lifestyle factors that may help

Certain lifestyle choices can play a role in influencing your SHBG levels, particularly in relation to factors like weight and insulin sensitivity. Discussing these with your GP can help you understand how they might apply to you.

• Weight management: Maintaining a healthy weight is one of the most significant lifestyle factors that can positively impact SHBG. Losing excess weight, especially abdominal fat, can be associated with an increase in SHBG levels.
• Dietary choices: A balanced diet that focuses on whole foods, lean proteins, healthy fats, and plenty of fruits and vegetables can support overall metabolic health. Reducing intake of processed foods, sugary drinks, and refined carbohydrates may help improve insulin sensitivity, which in turn can influence SHBG.
• Regular physical activity: Engaging in regular exercise, including both aerobic activity and strength training, can help with weight management and improve insulin sensitivity. This can be beneficial for hormone balance.
• Limiting alcohol intake: Excessive alcohol consumption can affect liver function and hormone balance, so moderating intake might be helpful.

Questions to discuss with your GP

If you have concerns about your hormone levels or are experiencing symptoms that might be related to hormonal imbalances, it's always best to have a conversation with your GP. Here are some questions you might consider discussing:

• What do my SHBG results mean in the context of my overall health and any symptoms I'm experiencing?
• Are my SHBG levels considered high or low for my age and sex, and what might be the potential causes?
• Could my current lifestyle factors, such as diet or weight, be influencing my SHBG levels?
• Are there any further tests you would recommend to investigate my hormone balance or related health conditions?
• What are the potential implications of my SHBG levels for my long-term health?
• Are there any lifestyle changes we could discuss that might help to optimise my hormone levels?