Sex hormone binding globulin and testosterone in men: what your SHBG levels really mean

Sex hormone binding globulin is more than a lab extra – your SHBG levels help explain why you can feel low testosterone symptoms even when your “total T” looks fine on paper.

“When guys see SHBG on their lab report they often skip past it, but that little number can tell us why a ‘normal’ testosterone result still feels anything but normal in real life.”

Alexander Grant, MD, PhD

The relationship

Before you can make sense of your SHBG levels, you need to know what is sex hormone binding globulin in the first place. Sex hormone-binding globulin, or SHBG, is a protein made mostly in your liver. Its job is to latch onto sex hormones in your blood, especially testosterone and a stronger form called dihydrotestosterone (DHT), and carry them around your body.^[1] In plain terms, SHBG is your hormone transport truck.

Here is the twist. Your cells can only use testosterone that is not tightly attached to SHBG. That usable portion is called free testosterone, plus a loosely bound fraction attached to another protein called albumin. Together those are often called bioavailable testosterone, meaning testosterone your tissues can actually access.

Most of the testosterone in a man’s bloodstream – roughly 70 percent – is bound to SHBG and is not directly available to cells. In adult men, typical SHBG levels fall somewhere between about 13.3 and 89.5 nanomoles per liter (nmol/L), though “normal” ranges vary slightly by lab. When SHBG is very high, it can lock away too much testosterone. When it is very low, it can be a red flag for metabolic problems even if free testosterone looks okay.

That is why many hormone specialists now request SHBG alongside total testosterone. Looking only at total testosterone can miss men whose SHBG levels are skewed and whose free testosterone is actually low or borderline.^[2] In those cases, adjusting for SHBG can change the diagnosis and the treatment plan.

How it works

SHBG as your hormone carrier protein

SHBG is a specialized carrier protein, a type of blood-borne “shuttle” that binds tightly to testosterone and DHT with high affinity, which means it holds on strongly.^[1] By binding these hormones, SHBG helps control how much free hormone is available at any moment and protects hormones from being broken down too quickly.

Free vs bound testosterone: why SHBG levels matter

In a typical man, only a small fraction of testosterone is free, a larger fraction is loosely bound to albumin, and the majority is tightly bound to SHBG. SHBG-bound testosterone is basically in storage. If SHBG levels climb, more testosterone gets locked up and free testosterone can drop, even if total testosterone stays in the “normal” range.

Studies in aging men show that symptoms like low sex drive, fatigue, and loss of muscle track more closely with free testosterone than with total testosterone.^[3] Meta-analyses indicate that symptomatic men with total testosterone below 350 ng/dL (≈12 nmol/L) are most likely to benefit from testosterone replacement therapy (TRT). If total testosterone is borderline, measuring free testosterone adds clarity; values below 100 pg/mL (≈10 ng/dL) support a diagnosis of hypogonadism.^[4],[6] In practice, many clinicians use 350 ng/dL for total or 100 pg/mL for free as decision thresholds when symptoms persist, and SHBG is essential for calculating free testosterone accurately.

What affects SHBG production in men

Your liver adjusts SHBG production based on several signals, including thyroid hormones, insulin, and nutritional status. High thyroid hormone (as in hyperthyroidism) and certain medications can increase SHBG. High insulin levels, often seen with obesity and insulin resistance, tend to suppress SHBG production.

Inflammation, liver disease, and androgens from outside the body (such as anabolic steroids) can also drive SHBG levels down. Because so many of these signals relate to metabolism, SHBG has become a surprisingly useful marker of overall metabolic and liver health in men, not just a side note on a hormone panel.

Age, weight, and SHBG: shifting balance over decades

Large population studies of middle-aged and older men show a consistent pattern: with age, SHBG levels tend to rise, while total testosterone slowly drifts down.^[5] Extra body fat, especially around the waist, tends to push in the opposite direction, lowering SHBG but often also reducing total testosterone. The result can be a complex mix of numbers where the lab printout does not match how a man feels.

Research from the European Male Ageing Study found that both high SHBG with low free testosterone and very low SHBG with metabolic problems were linked to poorer sexual function, lower energy, and worse physical performance.^[3],[5] This is why a single total testosterone value, without SHBG, can be misleading in older or heavier men.

Conditions linked to it

Abnormal SHBG levels are not a disease by themselves. They are often a marker of something else going on in a man’s body. Understanding these links helps you and your doctor decide whether to dig deeper.

Higher SHBG levels in men are often associated with:

Overactive thyroid (hyperthyroidism), which stimulates the liver to make more SHBG
Certain chronic liver conditions, such as cirrhosis
HIV infection and some antiretroviral drugs
Some anticonvulsant and anti-androgen medications
Normal aging, especially in lean men

When SHBG is high, free testosterone may be low even if total testosterone looks acceptable, which can contribute to classic low T symptoms.^[2],[3]

Lower SHBG levels in men are commonly associated with:

Obesity, especially central (belly) fat
Insulin resistance and type 2 diabetes
Metabolic syndrome, a cluster of high blood pressure, abnormal cholesterol, excess waist circumference, and high blood sugar
Nonalcoholic fatty liver disease
Underactive thyroid (hypothyroidism)
Use of anabolic steroids or very high-dose testosterone

Meta-analyses show that men with low SHBG are more likely to develop type 2 diabetes and metabolic syndrome over time, even after adjusting for testosterone levels. That suggests SHBG is acting as a barometer of underlying metabolic stress.

Limitations: Most of these data are observational. They show associations rather than direct cause and effect. For example, low SHBG may signal insulin resistance more than it causes it.

Symptoms and signals

SHBG itself does not cause symptoms you can feel. Instead, symptoms show up because of what your SHBG levels do to free testosterone or because of the condition driving SHBG up or down.

Signs your SHBG may be too high (often with low free testosterone):

Low sex drive or reduced interest in sex
More difficulty getting or keeping erections
Loss of morning erections
Fatigue or “flat” energy despite decent sleep
Reduced strength, slower gains from lifting, or loss of muscle mass
Increased body fat, especially around the midsection
Low mood, irritability, or decreased motivation
Normal or near-normal total testosterone on labs but symptoms that fit low T

Signs your SHBG may be very low (often tied to metabolic issues):

Weight gain, particularly belly fat
Higher blood pressure or rising cholesterol
Borderline or high fasting blood sugar
Acanthosis nigricans, a darker, velvety rash in skin folds that can signal insulin resistance
History of anabolic steroid use or very high-dose testosterone cycles
Total testosterone that looks low but free testosterone that is closer to normal

In both scenarios, the key mismatch to watch for is how you feel versus what your total testosterone report says. That mismatch is often what prompts a doctor to check SHBG levels and calculate free testosterone more precisely.^[2],[3]

What to do about it

You cannot biohack SHBG levels overnight, and you should not try to treat lab numbers in isolation. Here is a practical, evidence-based plan.

Get the right tests, at the right time

Ask your clinician for a hormone panel that fits your symptoms. For most men, that means at least:

Morning total testosterone, drawn between 7 and 11 a.m. on two separate days
SHBG, to interpret total testosterone and calculate free testosterone
Albumin, which helps laboratories estimate bioavailable testosterone
Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) if low testosterone is suspected
Prolactin and basic metabolic labs (fasting glucose, lipids, liver tests, thyroid tests) if there are broader health concerns

AUA and Endocrine Society guidelines both support using a total testosterone threshold around 350 ng/dL (≈12 nmol/L) in symptomatic men to consider TRT, and free testosterone below about 100 pg/mL (≈10 ng/dL) when total is borderline.^[4],[6] SHBG levels are essential for calculating free testosterone accurately, especially in older men, very lean men, and men with obesity or metabolic syndrome.

Address root causes and consider targeted treatment

There is no single “SHBG pill.” The goal is to treat what is driving your SHBG levels and your symptoms.

If SHBG is high and free testosterone is low:

Rule out and treat thyroid problems, liver disease, and medication effects where possible.
Evaluate for other causes of primary or secondary hypogonadism using guideline-based testing.^[4],[6]
Discuss TRT if you have consistent symptoms, repeatedly low free testosterone, and no major contraindications. TRT can raise total testosterone and free testosterone enough to overcome the binding effect of high SHBG.

If SHBG is very low:

Focus hard on metabolic health: reduce excess body fat, especially around the waist; improve diet quality; and increase daily movement.
Screen for and manage type 2 diabetes, prediabetes, and fatty liver disease, which are all linked to low SHBG.
Review any use of anabolic steroids or very high-dose testosterone and work with a physician on a safe exit plan.

Weight loss and resistance training have been shown to improve testosterone levels and can normalize SHBG in many obese men. For some men with low total testosterone and low SHBG, calculated free testosterone is still adequate; in those cases, focusing on lifestyle and metabolic treatment may make more sense than starting TRT right away.^[4],[6]

Myth vs Fact

Myth: “SHBG is a bad protein that steals your testosterone.”
Fact: SHBG is essential for moving hormones safely through your bloodstream. Problems arise mainly when SHBG levels are far above or below your personal sweet spot.
Myth: “Only total testosterone matters; SHBG is just an add-on test.”
Fact: In many men, especially older or heavier men, SHBG is the key to understanding whether their tissues are truly getting enough testosterone.
Myth: “Low SHBG always means low testosterone.”
Fact: Many men with obesity have low SHBG but normal or near-normal free testosterone. Low SHBG can be more of a metabolic warning light than a sign that you need TRT.
Myth: “You can reliably ‘hack’ SHBG levels with a supplement stack.”
Fact: Claims about herbs and over-the-counter pills changing SHBG levels in a meaningful, lasting way are not backed by solid human data. Focus first on proven levers like weight, sleep, and treating thyroid or liver disease.

Monitor, adjust, and think long-term

Once you and your clinician have a plan, track both how you feel and how your labs change over time.

Recheck testosterone, SHBG, and related labs after any major change: starting TRT, losing significant weight, or treating a thyroid or liver condition.
Give lifestyle changes at least 3 to 6 months to show their full effect on SHBG and testosterone.
Use consistent labs and morning blood draws so your results are as comparable as possible.
Revisit the decision about TRT periodically; your need can change as your SHBG levels, weight, and health status change.

For many men, SHBG becomes a useful long-term barometer. When it drifts back toward the middle of the reference range and your free testosterone and symptoms improve, you are usually moving in the right direction.

Bottom line

If you have ever wondered what is sex hormone binding globulin and why it shows up on your lab report, the answer is simple but powerful: it helps decide how much of your testosterone your body can actually use. SHBG levels that are too high or too low can explain why a man feels lousy with “normal” testosterone or why metabolic trouble is brewing under the surface. Work with a clinician who looks beyond a single total testosterone number, checks SHBG, and treats you – not just your lab values – with a focus on long-term metabolic and hormonal health.

References

Laurent MR, Hammond GL, Blokland M, et al. Sex hormone-binding globulin regulation of androgen bioactivity in vivo: validation of the free hormone hypothesis. Scientific reports. 2016;6:35539. PMID: 27748448
Goldman AL, Bhasin S, Wu FCW, et al. A Reappraisal of Testosterone’s Binding in Circulation: Physiological and Clinical Implications. Endocrine reviews. 2017;38:302-324. PMID: 28673039
Antonio L, Wu FC, O’Neill TW, et al. Low Free Testosterone Is Associated with Hypogonadal Signs and Symptoms in Men with Normal Total Testosterone. The Journal of clinical endocrinology and metabolism. 2016;101:2647-57. PMID: 26909800
Mulhall JP, Trost LW, Brannigan RE, et al. Evaluation and Management of Testosterone Deficiency: AUA Guideline. The Journal of urology. 2018;200:423-432. PMID: 29601923
Tajar A, Forti G, O’Neill TW, et al. Characteristics of secondary, primary, and compensated hypogonadism in aging men: evidence from the European Male Ageing Study. The Journal of clinical endocrinology and metabolism. 2010;95:1810-8. PMID: 20173018
Bhasin S, Brito JP, Cunningham GR, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. The Journal of clinical endocrinology and metabolism. 2018;103:1715-1744. PMID: 29562364