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Hormones

SHBG (Sex Hormone Binding Globulin)

SHBG is a glycoprotein produced primarily by the liver that binds to sex hormones — testosterone, dihydrotestosterone (DHT), and oestradiol — and regulates their bioavailability. Only the unbound (free) fraction of testosterone is biologically active, so SHBG levels directly determine how much testosterone your body can actually use. SHBG is influenced by thyroid function, insulin levels, liver health, and body composition.

Optimal Ranges

Clinical (NHS) Range

18.3-54.1 nmol/L (male)

nmol/L

Performance-Optimised Range

25-45 nmol/L

nmol/L

The clinical range defines what is considered medically “normal” — broad enough to cover 95% of the population. The performance range reflects where research and clinical experience suggest most people feel and function at their best.

Why It Matters

Why SHBG matters for performance

A man can have a normal total testosterone level but still experience symptoms of low T if his SHBG is too high — because most of his testosterone is bound and unavailable. Conversely, very low SHBG can lead to excess free testosterone converting to oestrogen via aromatase, causing its own set of problems. SHBG is a critical piece of the hormonal puzzle that is often missed in standard blood tests. Elevated SHBG is associated with hypothyroidism, liver disease, and caloric restriction; low SHBG is linked to insulin resistance, obesity, and type 2 diabetes risk.

Symptoms

Signs your levels may be off

Low / Deficiency

  • Symptoms of excess free testosterone (acne, hair loss, aggression)
  • Increased oestrogen conversion
  • May indicate insulin resistance or metabolic syndrome

High / Excess

  • Fatigue despite normal total testosterone
  • Low libido and erectile dysfunction
  • Muscle wasting and difficulty building mass
  • Depression and brain fog

Dietary Sources

Foods that support SHBG levels

No direct dietary sources — SHBG is produced by the liverMaintaining healthy insulin levels (low-GI diet) helps normalise SHBGAdequate protein intake supports liver functionCruciferous vegetables support healthy oestrogen metabolismModerate alcohol (excess lowers SHBG acutely but chronic use raises it)

Supplementation

Evidence-based supplementation

SHBG itself cannot be supplemented — the goal is to address the underlying cause of abnormal levels. For high SHBG: check thyroid function (hypothyroidism raises SHBG), ensure adequate caloric intake (undereating raises SHBG), and consider boron supplementation (6-10mg daily has been shown to reduce SHBG by ~10% in some studies). For low SHBG: improve insulin sensitivity through exercise and weight management, reduce refined carbohydrates, and address any fatty liver disease. Nettle root extract (Urtica dioica) is marketed as an SHBG modulator but clinical evidence is limited to in-vitro studies.

Research

Key study

Sex hormone-binding globulin and risk of type 2 diabetes in women and men

Ding EL, Song Y, Manson JE, et al.

New England Journal of Medicine (2009)

DOI: 10.1056/NEJMoa0804381

Related Biomarkers

Hormones

Total Testosterone

Optimal: 20-30 nmol/L

Hormones

DHEA-Sulphate

Optimal: 7.0-12.0 µmol/L

Thyroid

TSH (Thyroid Stimulating Hormone)

Optimal: 1.0-2.0 mIU/L

Metabolic

HbA1c (Glycated Haemoglobin)

Optimal: 20-34 mmol/mol (below 5.4%)

Related Guides

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Complete Guide to Blood Tests

What to test and why it matters

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This content is for educational purposes only and does not constitute medical advice. Your data suggests areas for optimisation, but any concerns should be discussed with a qualified healthcare professional. If your results flag values outside safe ranges, we recommend consulting your GP.