SHBG is a protein produced by the liver that binds to sex hormones, primarily testosterone and estradiol, regulating how much of each is free and biologically active. Changes in SHBG shift the balance between bound (inactive) and free (active) hormone.
SHBG is critical for interpreting testosterone and estradiol results because it determines how much hormone is actually available to tissues. High SHBG lowers free testosterone even when total is normal, a common cause of low-T symptoms with "normal" labs. Low SHBG often signals insulin resistance, fatty liver, or metabolic dysfunction. SHBG naturally rises with age, which is one reason testosterone symptoms can worsen even when total testosterone looks unchanged.
Optimal SHBG: 20-50 nmol/L.
Typically re-tested every 12 weeks.
SHBG is a glycoprotein made mainly by the liver that binds sex hormones in the blood and regulates how much of them remains biologically available.
Once testosterone, dihydrotestosterone and estradiol enter circulation, very little of them travels alone. Most is carried, tightly by SHBG and loosely by albumin, and only a small unbound fraction is generally regarded as free to enter cells and act on receptors. SHBG binds androgens more tightly than it binds estrogens, so a change in SHBG does not move every sex hormone by the same amount.
That makes SHBG a dial on hormone availability rather than a hormone itself. A total testosterone result measures everything in the tank. SHBG indicates how much of that tank is locked up. Two people with an identical total testosterone number can have quite different free testosterone levels if their SHBG differs, which is why labs regard the two as a pair.
SHBG production is not fixed either. Research describes SHBG as a hepatokine, a protein released by the liver whose output responds to metabolic signals including insulin, thyroid hormone, estrogens and the fat content of the liver itself[1]. That dual identity, part hormone transporter and part liver signal, is why the marker turns up in both hormone panels and metabolic work-ups.
SHBG matters for two separate reasons, because it changes how your sex hormone results should be read, and because the level itself tracks with metabolic health.
The first reason is interpretive. If SHBG is high, more of your testosterone is bound and less is free, so symptoms of low androgen activity can appear even when total testosterone sits comfortably inside the reference range. If SHBG is low, the opposite happens and free hormone runs proportionally higher than the total suggests. Without SHBG, a sex hormone panel is missing the context that makes it readable.
The second reason is metabolic. Low SHBG is consistently associated with insulin resistance, central adiposity and higher risk of type 2 diabetes, and research suggests the liver's handling of fat and glucose is part of that link rather than a coincidence[1]. In men, low androgen status and type 2 diabetes cluster together often enough that the relationship has been reviewed as a topic in its own right[2], and comprehensive clinical guidance on the care of patients with obesity lists hypogonadism among the conditions that accompany excess adiposity[3].
In women, a low SHBG is one of the more recognisable laboratory features of polycystic ovary syndrome, where it tends to fall alongside insulin resistance and leaves a larger free androgen fraction in circulation[4]. Studies indicate SHBG may function as an early signal of the metabolic side of that picture rather than a late consequence of it[5].
None of that turns a single SHBG value into a diagnosis. It makes SHBG a useful early read on a direction of travel, which is worth reviewing with a clinician alongside the rest of your panel.
A typical adult laboratory reference range for SHBG runs from about 10 to 80 nmol/L, while FitScript's optimal range is 20 to 50 nmol/L, and 40 to 120 nmol/L in women.
| Range | Value (nmol/L) |
|---|---|
| Standard lab reference range, typical adult | 10 to 80 |
| FitScript optimal range | 20 to 50 |
| FitScript optimal range, women | 40 to 120 |
A German population study (KORA) measured SHBG in 519 healthy adults aged 32 to 90.[13] Women ran higher than men, and in men the range rose in the oldest group.[13]
| Sex | Age | Reference range (nmol/L) |
|---|---|---|
| Men | 30 to 39 | 8.13 to 79.25 |
| Men | 40 to 49 | 18.38 to 92.23 |
| Men | 50 to 59 | 14.56 to 102.71 |
| Men | 60 to 90 | 29.38 to 125.90 |
| Women | Premenopausal (32 to 54) | 32.94 to 162.36 |
| Women | Postmenopausal (50 to 90) | 32.00 to 176.78 |
Ranges are the 2.5th to 97.5th percentiles, split by age decade in men and by menopausal status in women. Your own lab's printed range is the one to read your result against, since values depend on the assay used.
Reference ranges vary by laboratory, age and sex, so always read your result against the range printed on your own report. Different assays and different reference populations produce different numbers for the same blood.
FitScript's optimal ranges are optimization targets, not diagnostic cut-offs. A result inside the standard reference range but outside the optimal range is not a disease finding. It is a prompt to look at the surrounding markers and at how you feel.
Two details matter when comparing results. SHBG is usually reported in nmol/L, so check the units before assuming two reports disagree. And because SHBG shifts with sex, age and hormonal status, a value that reads as unremarkable for one person can be notable for another.
A high SHBG result means more of your circulating sex hormone is bound and a smaller proportion is free, which can produce symptoms of low hormone activity even when total testosterone or total estradiol looks adequate.
People with a high result and a low free androgen fraction often report low libido, flat mood, poor training recovery, fatigue that sleep does not fix, and in men reduced morning erections. Many people with a high SHBG report nothing at all, which is why the number is interpreted next to symptoms rather than on its own.
Common contributors to a high SHBG include an overactive thyroid, liver conditions that alter hepatic protein output, oral estrogen in contraceptives or menopausal hormone therapy, pregnancy, advancing age in men, prolonged low energy availability or very low body fat, and high endurance training loads. Research suggests structured exercise training shifts anabolic and catabolic hormone profiles in older adults, although findings differ by programme type and duration[6].
For long-term health, a high SHBG is generally regarded as a more benign finding than a low one, because it tends to track with better insulin sensitivity and leaner body composition. The concern is less the number itself and more what it is pointing at, whether that is thyroid overactivity, liver strain, or an energy intake that is not matching training load. A markedly high result, especially with symptoms, is worth discussing with a clinician promptly so the underlying cause can be looked at rather than the number alone.
A low SHBG result means less hormone is bound and a larger fraction circulates free, and it is most often a metabolic signal rather than a sex hormone problem.
Reported symptoms differ by sex. Women with a low result and a higher free androgen fraction may notice acne, scalp hair thinning, unwanted facial or body hair, and irregular or absent cycles. Men frequently report nothing specific from the SHBG itself and instead notice the company it keeps, such as expanding waist circumference, afternoon energy crashes, poor sleep and reduced training response.
Common contributors include insulin resistance, excess visceral fat, fat accumulation in the liver, an underactive thyroid, androgen use, and conditions associated with growth hormone excess. The adiposity link is not just correlational. A Mendelian randomization study with meta-analysis found that adiposity across childhood, adolescence and adulthood is associated with risk of polycystic ovary syndrome, a condition in which SHBG is characteristically low[7].
On the long view, a persistently low SHBG is associated with insulin resistance and the metabolic pattern that precedes type 2 diabetes[1], and in men it travels with the androgen and glucose relationship described in the clinical literature[2]. In women with polycystic ovary syndrome, the broader picture also carries reproductive implications, and reviews have examined its association with recurrent pregnancy loss[8].
Again, one low reading is an observation, not a verdict. The useful next step is a repeat test with the surrounding metabolic markers and a conversation with a clinician about what the pattern suggests for you.
SHBG moves with testing conditions, medications and metabolic habits, so the same person can produce different numbers in different months without anything being wrong with the lab.
Testing conditions. SHBG generally does not swing as sharply across the day as total testosterone, but it is still read best when the draw conditions are consistent. Use the same laboratory where possible, since assays differ, and keep the timing, fasting status and recent training load broadly similar between tests. Acute illness, a heavy training block or a sharp change in body weight can all shift a single reading, so trends over several tests say more than any one result.
Medications. Oral estrogen-containing contraceptives and oral menopausal hormone therapy are associated with higher SHBG, because they pass through the liver before reaching the circulation. Medications that produce substantial weight loss can change the picture indirectly, and a systematic review and meta-analysis of glucagon-like peptide 1 receptor agonists reported effects on male reproductive hormone measures[9]. Any prescription medication, including GLP-1 medications and hormone therapy, is something a licensed provider evaluates for appropriateness.
Habits. Body composition, liver fat and insulin signalling are the main levers, which is why SHBG tends to move with sustained changes in weight, training and diet quality rather than with short experiments. Physical activity appears in the research in unexpected forms, and one study reported an association between neighbourhood walkability and sex steroid hormone levels in women[10]. Some widely repeated claims do not hold up. An expanded and updated meta-analysis of clinical studies found that neither soy nor isoflavone intake affects male reproductive hormones[11]. Supplement evidence remains early and context-specific, and a systematic review and meta-analysis of N-acetylcysteine in polycystic ovary syndrome is one example of research still being assembled[12], which is a conversation for a clinician rather than a self-directed experiment.
The detailed question of how to raise or lower a result is covered separately. The short version is that SHBG responds to metabolic health over months, not to quick fixes.
SHBG is measured from a standard venous blood draw as part of hormone bloodwork, and it is most informative when run in the same panel as the sex hormones it governs.
FitScript includes SHBG within its hormone bloodwork, part of 150+ biomarkers tested per year, so the result arrives with total and free testosterone, estradiol and metabolic markers rather than in isolation. Atlas, FitScript's AI health advisor, reads the value in that context, flags where it sits against both the standard reference range and the optimal range, and writes your FitScript from the pattern across your results. Repeat testing is what makes the marker useful, because a direction over three results carries more information than a single point.
Where a result raises a question that might call for prescription hormone therapy or any other medication, a licensed provider reviews the full picture and decides whether something is appropriate. Nothing on a lab report by itself establishes that a medication is needed.
SHBG is almost never interpreted alone. These are the markers that give it meaning.
These are typically ordered together within Hormone Panel for men and Hormone Panel for women rather than one at a time, because the ratios are what carry the signal.
Read the number, then read it in company. Note where it sits against your own laboratory's reference range and against the optimal range, check whether free testosterone or free androgen activity moves in the direction the SHBG would predict, and look at the metabolic markers beside it. Then retest at a sensible interval under similar conditions and watch the trend.
A value outside the standard range is a reason for a conversation, not a conclusion, and a result that comes with persistent symptoms is worth discussing with a clinician promptly. Bring your results and any questions about medication or hormone therapy to a clinician or licensed provider who can review your full history. This article is educational and is not medical advice.
Calculators that use SHBG:
It measures the concentration of sex hormone-binding globulin, a liver-made protein that binds testosterone, dihydrotestosterone and estradiol in the bloodstream. The value indicates how much of your circulating sex hormone is bound and therefore how much remains free and available to tissues. It is reported in nmol/L and is most informative alongside total and free testosterone.
A typical adult laboratory reference range runs from about 10 to 80 nmol/L, though ranges vary by lab, age and sex, so read your result against the range printed on your own report. FitScript's optimal range is 20 to 50 nmol/L, and 40 to 120 nmol/L in women. Optimal ranges are optimization targets, not diagnostic cut-offs.
It means a larger share of your sex hormones is bound, so free hormone can be lower than a total testosterone result suggests. Common contributors include an overactive thyroid, liver conditions, oral estrogen, pregnancy, advancing age in men, prolonged low energy availability and high endurance training loads. A markedly high value with symptoms is worth discussing with a clinician promptly.
Low values are most often associated with insulin resistance, excess visceral fat, fat accumulation in the liver, an underactive thyroid and androgen use. In women, a low result is one of the recognisable laboratory features of polycystic ovary syndrome. A single low reading is an observation rather than a diagnosis and should be reviewed with a clinician alongside metabolic markers.
Fasting requirements depend on the other markers in the panel rather than on SHBG itself, so follow the instructions your lab or provider gives for the full draw. What matters most for SHBG is consistency, meaning the same lab, similar timing and similar recent training and weight conditions between tests, so that trends are readable.
SHBG generally rises gradually with age in men, which is one reason free testosterone can decline faster than total testosterone over the decades. Age is only one input though, since thyroid status, liver health, insulin signalling, medications and body composition all influence the level at any age.
Oral estrogen-containing contraceptives are associated with higher SHBG, because oral estrogen passes through the liver before entering the general circulation and increases hepatic protein output. This is expected rather than alarming, but it should be noted when interpreting free testosterone or free androgen results. Discuss any contraceptive or hormone medication with a licensed provider.
No. Free testosterone is the unbound fraction of the hormone itself, while SHBG is the protein that determines how large that free fraction is. They move in opposite directions, so a rising SHBG tends to accompany a falling free testosterone even when total testosterone is unchanged. Labs regard the two as results to be read together.