Hormones · Bioavailability gatekeeper

SHBG

Sex hormone-binding globulin (SHBG) is a liver-produced glycoprotein that binds testosterone and estradiol, removing them from immediate cellular availability. SHBG is the single largest determinant of how much of a measured total testosterone is actually biologically active. High SHBG can mask adequate total T as low free T; low SHBG often reflects insulin resistance or hepatic steatosis.

Women average ~40-120 nmol/L (about 2x male levels). Oral estrogens (OCPs, oral HRT) dramatically raise SHBG (often 2-4x baseline); transdermal estrogen does not. Low SHBG independently predicts incident type 2 diabetes in women. Pregnancy raises SHBG 5-10x.

Optimal range (women)

reproductive · perimenopause · postmenopause · pregnancy

50–120nmol/L

Cycle: Relatively stable across the cycle (< 10% variation).

Clinical "normal"

18–144 nmol/L

Avg. cost (US)

$45

Test frequency

With total T, every 3–6 months

When to measure

Any cycle day in non-pregnant women. Note current OC/HRT use on the requisition.

How to measure

Standard immunoassay.

Average cost

≈ $45 cash price. Often covered by insurance with relevant ICD-10.

Why this biomarker matters

SHBG sits at the intersection of liver health, insulin signaling, and sex hormone bioavailability. Production rises with thyroid hormone excess, estrogen exposure, low-calorie or low-carbohydrate diets, advanced age, and aggressive caloric restriction. Production falls with insulin resistance, obesity, non-alcoholic fatty liver disease, hypothyroidism, growth hormone excess, and high-protein high-fat hypercaloric intake. A low SHBG (under 20 nmol/L in a non-obese adult man) is a useful proxy biomarker for hepatic insulin resistance, often appearing before fasting insulin or HbA1c becomes overtly abnormal. Mendelian randomization studies suggest SHBG itself may not be causally protective; rather, it tracks the upstream metabolic state. Treating the underlying insulin resistance, through weight loss, training, and dietary changes, raises SHBG back into the healthy range over weeks to months. A high SHBG (above 60 to 70 nmol/L in men) is often seen in chronic underfueling, hypogonadal hyperthyroidism, advanced age, and certain liver diseases including viral hepatitis. The clinical consequence is reduced free testosterone for any given total T value, which can produce androgen-deficiency symptoms in men whose total testosterone reads "normal" on paper.

Signs your level is off

Symptoms if low

Low SHBG (< 30 nmol/L) is a red flag for insulin resistance, PCOS, metabolic syndrome, fatty liver, hypothyroidism, or androgen excess — not symptomatic per se but flags downstream risk.

Symptoms if high

High SHBG (often > 150-200 nmol/L) seen with hyperthyroidism, oral contraceptive/oral estrogen use, pregnancy, anorexia, liver disease — may cause functional androgen deficiency (low free T despite normal total T).

If your level is low

Nettle: mild diuretic

Supplement

Berberine or inositol· Berberine 500 mg 2-3x/day with meals; or inositol 4 g/day

Form: capsule/powder

Improves insulin sensitivity, which raises hepatic SHBG production

Foods

Mediterranean / low-glycemic pattern
reduce refined carbs and fructose
increase fiber
limit alcohol (alcohol suppresses SHBG)

Lifestyle

weight loss if overweight
resistance training
sleep optimization
treat NAFLD if present

Medication (if prescribed)

Metformin (if PCOS / insulin resistance)· 500-2000 mg/day

Form: Oral

Reference only. Speak with a licensed clinician before any prescription intervention.

Caution: Low SHBG often co-occurs with insulin resistance — screen with fasting insulin, HOMA-IR, and fatty liver imaging.

If your level is high

Metformin: GI upset

Supplement

None routinely indicated· N/A

Form: N/A

Address underlying cause

Foods

balanced macronutrients
adequate protein

Lifestyle

screen for hyperthyroidism (TSH, free T4)
review meds (anticonvulsants, OCPs)

Medication (if prescribed)

Re-evaluate exogenous estrogen exposure· Switch oral to transdermal estradiol if HRT is the cause

Form: Transdermal patch/gel

Reference only. Speak with a licensed clinician before any prescription intervention.

Caution: Markedly high SHBG with low free T may cause androgen-deficiency symptoms — do not over-treat if asymptomatic. In pregnancy elevation is physiologic.