SHBG (Sex Hormone Binding Globulin): What High or Low Levels Mean
Medically reviewed by Medical Advisory Board Last reviewed 2026-05-13
The protein that controls how much testosterone and estrogen your body can actually use
Sex hormone binding globulin (SHBG) is a liver-produced protein that binds testosterone and estrogen, regulating how much of each hormone is bioavailable. High SHBG reduces free testosterone; low SHBG increases free estrogen — both cause symptoms.
SHBG is the master regulator of sex hormone bioavailability. Produced primarily by the liver, SHBG binds testosterone with high affinity (making it biologically inactive) and estrogen with somewhat lower affinity. Changes in SHBG levels directly alter the ratio of free-to-bound hormones — and therefore the symptoms you experience.
Understanding SHBG is essential because it explains many clinical scenarios where total hormone levels look normal but symptoms persist. A man with total testosterone of 600 ng/dL and SHBG of 70 nmol/L has less bioavailable testosterone than a man with total T of 450 ng/dL and SHBG of 25 nmol/L. Without measuring SHBG, you're only seeing half the picture.
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| Population | Low | Optimal | High |
|---|---|---|---|
| Men (20–50) | <20 nmol/L | 20–50 nmol/L | >50 nmol/L |
| Men (50+) | <25 nmol/L | 25–60 nmol/L | >60 nmol/L |
| Premenopausal women | <30 nmol/L | 30–80 nmol/L | >80 nmol/L |
| Postmenopausal women | <25 nmol/L | 25–70 nmol/L | >70 nmol/L |
SHBG increases approximately 1.6% per year in men after age 30, steadily reducing free testosterone even when total T remains stable.
What Causes High SHBG
- Aging — SHBG rises progressively after age 30 in men
- Hyperthyroidism — thyroid hormones directly stimulate hepatic SHBG production
- Estrogen exposure — oral contraceptives, HRT, and environmental estrogens increase SHBG
- Liver disease — hepatitis and cirrhosis can increase SHBG production
- Low-calorie diets — caloric restriction raises SHBG, potentially reducing free T
- Anorexia nervosa — markedly elevated SHBG from malnutrition
- Anticonvulsants — carbamazepine, phenytoin increase SHBG via hepatic enzyme induction
High SHBG in Females
High sex hormone binding globulin in females often means less free testosterone and less free estradiol are available to tissues, even when total hormone levels look normal. Common causes include oral contraceptives, oral estrogen therapy, hyperthyroidism, liver conditions, under-eating, significant weight loss, and some seizure medications. Symptoms can overlap with low androgen or low estrogen states: low libido, fatigue, vaginal dryness, poor exercise response, and mood changes. Interpreting high SHBG in women requires total testosterone, free testosterone, estradiol, thyroid markers, medication review, and menstrual or menopause status.
What Causes Low SHBG
- Obesity / insulin resistance — insulin directly suppresses hepatic SHBG production. A HOMA-IR increase of 1 unit reduces SHBG by approximately 10%
- Hypothyroidism — low thyroid hormones reduce SHBG production
- Type 2 diabetes — hyperinsulinemia is a potent SHBG suppressant
- Polycystic ovary syndrome (PCOS) — low SHBG is both a feature and diagnostic marker
- Anabolic steroid use — exogenous androgens suppress SHBG
- Growth hormone excess — acromegaly lowers SHBG
Low SHBG in men means more free testosterone but also more free estradiol — which can cause gynecomastia, water retention, and mood changes. In women, low SHBG elevates free androgens, contributing to acne, hirsutism, and PCOS symptoms.
How to Lower or Raise SHBG Naturally
Whether you want SHBG to go down or up depends on which direction is causing your symptoms — there's no universal "fix." These strategies address the underlying drivers rather than the SHBG number itself.
Strategies That Tend to Lower SHBG
- Resistance training: Regular strength training modestly lowers SHBG while supporting healthy free testosterone.
- Adequate (not excessive) caloric intake: Chronic under-eating and very-low-calorie diets raise SHBG; eating enough to support training and daily activity helps keep it from climbing.
- Zinc: 30–45 mg/day is a commonly cited intake in the same context as the SHBG-lowering strategies used for free-testosterone support (see the FAQ below).
- Boron: A small one-week study in Journal of Trace Elements in Medicine and Biology (Naghii et al., 2011) found that 10 mg/day of boron lowered SHBG by about 9%, alongside a 28% rise in free testosterone and a 39% drop in estradiol, in healthy men. This is a very small, short-duration study — evidence for boron's effect on SHBG is preliminary, not a settled recommendation.
Strategies That Tend to Raise SHBG
- Improving insulin sensitivity: Since hyperinsulinemia is one of the strongest suppressors of hepatic SHBG production, the same interventions that improve insulin resistance — weight loss, reduced refined-carbohydrate intake, regular exercise — tend to raise SHBG over time. This is why SHBG often rises after meaningful weight loss.
- Treating hypothyroidism: Correcting low thyroid hormone levels with appropriate treatment restores hepatic SHBG production toward normal.
- Flaxseed: Flaxseed lignans are theorized to raise SHBG by inhibiting aromatase and stimulating hepatic SHBG synthesis, and some small trials in postmenopausal women have found a measurable SHBG increase with daily flaxseed intake — but other trials have found no significant change, so the evidence is mixed rather than settled.
- Reducing oral estrogen exposure: For women on oral contraceptives or oral HRT, switching to a non-oral (transdermal/vaginal) form lowers the liver's first-pass estrogen exposure, which is the main driver of SHBG elevation from these medications — discuss any medication change with a prescriber first.
Because SHBG shifts are usually a downstream effect of an underlying driver (body composition, thyroid status, insulin sensitivity, medication), retesting SHBG 8–12 weeks after a genuine change to one of these factors is more informative than trying to move the number directly.
How to test your hormones at home
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Frequently Asked Questions
What does high SHBG mean for men?
High SHBG in men reduces bioavailable (free) testosterone, potentially causing low-T symptoms — fatigue, reduced libido, loss of muscle mass — even when total testosterone is in the normal range. Common causes include aging, hyperthyroidism, liver conditions, and certain medications. If total T is normal but symptoms are present, check SHBG and free testosterone.
What does sex hormone binding globulin high female mean?
High SHBG in females means more testosterone and estrogen are protein-bound and less is bioavailable. It is commonly linked to oral contraceptives, oral estrogen, hyperthyroidism, liver conditions, under-eating, or medication effects. Interpretation should include symptoms and free hormone levels, not SHBG alone.
How can I lower SHBG?
If SHBG is elevated: address underlying causes (thyroid dysfunction, medications, liver issues). Nutritional strategies include adequate protein intake, zinc supplementation (30–45 mg/day), and maintaining sufficient caloric intake. Resistance training and maintaining healthy body composition help. For women on oral contraceptives, switching to non-oral forms may reduce SHBG.
Is SHBG included in standard bloodwork?
No. SHBG is not part of standard bloodwork panels. It must be specifically ordered (CPT code 84270). Most doctors test only total testosterone, which can appear normal even when free testosterone is low due to elevated SHBG. Always request SHBG alongside total testosterone for an accurate picture.
Is SHBG the same as testosterone?
No. SHBG (sex hormone binding globulin) is a separate protein made by the liver — it doesn't produce or replace testosterone, it binds to it. Total testosterone measures all the testosterone in your blood, whether it's bound to SHBG, loosely bound to albumin, or free. SHBG determines how much of that total testosterone is actually available for your cells to use: more SHBG means less free testosterone for a given total, and less SHBG means more. That's why two people can have identical total testosterone and very different symptoms if their SHBG differs.
Does PCOS cause high or low SHBG?
PCOS is characteristically associated with low SHBG, not high. The insulin resistance common in PCOS suppresses the liver's SHBG production, which in turn raises free androgens (including free testosterone) — contributing to acne, hirsutism, and irregular cycles. Low SHBG is considered both a feature of PCOS and a diagnostic clue: a woman with irregular periods and an unexpectedly low SHBG on routine bloodwork warrants a PCOS workup even before androgen levels are reviewed.
Does TRT or anabolic steroid use lower SHBG?
Yes. Exogenous testosterone (TRT) and especially supraphysiologic anabolic steroid doses suppress hepatic SHBG production, often significantly. This is part of why free testosterone can rise faster and higher than total testosterone in the first weeks of TRT — less of the administered hormone is being mopped up by SHBG. Some men on TRT try to deliberately raise SHBG back toward baseline; there's no established protocol for doing this safely on-cycle, and providers typically monitor free/total testosterone and hematocrit directly rather than chasing a specific SHBG number. Discuss any SHBG shift on TRT with the prescribing clinician rather than self-adjusting dose.
Does SHBG change during pregnancy?
Yes, substantially. Rising estrogen during pregnancy drives a large increase in hepatic SHBG production — levels can climb several-fold above baseline by the third trimester. This is a normal, expected physiological change, not a marker of dysfunction. It does lower free (bioavailable) testosterone, since testosterone production doesn't rise nearly as much as SHBG's binding capacity does. Free estradiol, by contrast, still rises substantially in pregnancy despite the higher SHBG — placental estrogen production increases so dramatically that it outpaces the increased binding capacity. Because of this, standard non-pregnant SHBG reference ranges do not apply during pregnancy, and SHBG is not typically used as a standalone diagnostic marker in pregnant patients.
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