Sex Hormone Binding Globulin

Sex Hormone–Binding Globulin (SHBG) is a glycoprotein produced primarily by the liver that binds to sex hormones — mainly testosterone and oestradiol — and controls how much of these hormones are “free” and biologically active in the body. SHBG acts as the regulator of hormonal balance, determining how much oestrogen and testosterone can reach tissues that influence fertility, mood, metabolism, and bone health.

By managing the balance between bound and unbound hormones, SHBG plays an essential role in reproductive and metabolic health. It is also a key biomarker used to evaluate polycystic ovary syndrome (PCOS), androgen excess, oestrogen deficiency, and to assess cardiometabolic risk.

SHBG maintains stability within the body’s hormonal network.

• Low SHBG levels mean more free androgens or estrogens are circulating, which can occur in PCOS, insulin resistance, hypothyroidism, or obesity. This often contributes to symptoms such as acne, excess hair growth, and irregular menstrual cycles.
  

• High SHBG levels reduce the amount of active (free) hormones and are often linked to hyperthyroidism, estrogen-dominant states, or oral contraceptive use, potentially causing low libido, fatigue, and mood changes.
  

Because SHBG reflects the interaction between liver health, thyroid function, and metabolic balance, it is an important indicator for identifying underlying causes of hormonal imbalance, reproductive challenges, or metabolic dysfunction.

SHBG levels are dynamic and influenced by multiple internal and external factors:

1. Hormonal Status: Oestrogen stimulates SHBG production, while androgens and insulin suppress it.
   

2. Body Composition: Higher body mass index (BMI) and insulin resistance reduce SHBG production, while weight loss and improved insulin sensitivity raise it.
   

3. Age and Menopause: SHBG levels decline with age and are generally lower postmenopause due to reduced oestrogen production.
   

4. Medications: Oral contraceptives and hormone replacement therapy (HRT) can increase SHBG because of their oestrogenic activity.
   

5. Liver Function: Since SHBG is produced in the liver, liver disease or dysfunction can lower its synthesis.

Childhood and Puberty

SHBG levels are high in early childhood but decrease at puberty as androgen production increases, helping to regulate the onset of menstrual cycles and sexual maturation.

Reproductive Years

During reproductive years, SHBG levels fluctuate with the menstrual cycle and are influenced by oestrogen, insulin, and thyroid activity. Oral contraceptives and pregnancy typically elevate SHBG, while PCOS, metabolic syndrome, or obesity lower it.

Perimenopause

As oestrogen levels fluctuate during perimenopause, SHBG gradually declines, leading to relatively higher free androgen activity. This can manifest as hair thinning, facial hair growth, and changes in skin or body composition.

Postmenopause

After menopause, SHBG levels fall further due to reduced oestrogen. This shift can increase free testosterone levels and influence bone density, libido, and metabolic health. Persistently high SHBG in this stage may suggest thyroid imbalance or liver dysfunction.

If SHBG Is Low

• Improve Insulin Sensitivity: Follow a low-glycemic diet rich in fiber, lean proteins, and omega-3 fats (from fish, chia, or flaxseed).

• Support Liver Function: Limit alcohol and processed foods; increase cruciferous vegetables and hydration.

• Address Hormonal Root Causes: Investigate PCOS, hypothyroidism, or metabolic syndrome with your practitioner.

• Exercise Regularly: Combine resistance training with aerobic movement to improve insulin and hormone balance.
  

If SHBG Is High

• Evaluate Oestrogen and Thyroid Function: High SHBG may indicate excessive oestrogen or thyroid overactivity.

• Ensure Adequate Nutrition: Include sufficient dietary protein and healthy fats to support hormone transport and metabolism.

• Review Medications: Oral contraceptives or hormone therapy may need adjustment.

• Prioritise Resistance Training: Building lean muscle mass can improve hormonal balance and lower excessive SHBG binding.

Optimal Range by life stage (nmol/L)

Premenopausal

50–80 nmol/L

• Reflects healthy oestrogen influence and balanced insulin function.

Perimenopausal

45–70 nmol/L

• Begins to decline with fluctuating oestrogen; androgen symptoms may appear.

Postmenopausal

40–60 nmol/L

• Supports bone, mood, and libido balance with lower oestrogen levels.

• Falling below range increases risk for insulin resistance and type 2 diabetes, while persistently high levels may be linked to bone loss, fatigue, or thyroid dysfunction.

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