Sex hormone-binding globulin (SHBG) rises in men for a wide range of reasons, from an overactive thyroid gland or normal aging to specific medications, calorie restriction, and inherited gene variants. Because SHBG binds testosterone in the bloodstream and limits how much of it is available to tissues, an unexpectedly high level can mimic or worsen the symptoms of low testosterone even when total testosterone looks normal on paper. Understanding what drives SHBG up matters for interpreting hormone panels correctly and, in some cases, for identifying an underlying condition that needs attention on its own terms.
How the Liver Controls SHBG Production
SHBG is a protein manufactured primarily by the liver. Its production hinges on a transcription factor called HNF-4α, which acts as a master switch for the SHBG gene. Signals that boost HNF-4α activity tend to raise SHBG, while signals that suppress it tend to lower SHBG. Thyroid hormones and estrogens both stimulate SHBG production through this pathway, whereas simple sugars like glucose and fructose drive fat synthesis inside liver cells, which in turn lowers HNF-4α and pulls SHBG down.1PubMed. Sex hormone-binding globulin gene expression in the liver: drugs and the metabolic syndrome This liver-centric mechanism explains why so many seemingly unrelated conditions, from thyroid disease to insulin resistance to certain drugs, all end up affecting the same blood test.
Hyperthyroidism Is One of the Strongest Drivers
An overactive thyroid gland is one of the most potent and well-documented causes of elevated SHBG in men. Excess thyroid hormone increases HNF-4α gene expression in the liver and simultaneously reduces a fatty acid (palmitate) that normally holds HNF-4α in check, creating a double push toward more SHBG production.2Journal of Molecular Endocrinology. Thyroid hormones act indirectly to increase sex hormone-binding globulin production by liver via hepatocyte nuclear factor-4α In clinical studies, hyperthyroid patients consistently show high SHBG, while hypothyroid patients show low or normal levels.3PubMed. Sex hormone-binding protein in hyperthyroxinemic patients: a discriminator for thyroid status in thyroid hormone resistance and familial dysalbuminemic hyperthyroxinemia The relationship is tight enough that SHBG correlates positively with free thyroid hormone concentrations in both men and women, and when hyperthyroid patients receive treatment to normalize their thyroid, SHBG concentrations come back down.4PubMed. Opposite effects of thyroid hormones on binding proteins for steroid hormones (sex hormone-binding globulin and corticosteroid-binding globulin) in humans
A prospective study tracking men with primary thyroid dysfunction confirmed this pattern: in the hyperthyroid group, SHBG fell significantly during treatment as thyroid hormone levels normalized.5PubMed Central. Primary thyroid dysfunction and changes in the gonadal axis and SHBG in adult men: a prospective cohort study If your SHBG is high and nobody has checked your thyroid, that is one of the first things worth ruling out.
Aging and the Slow Upward Drift
Even in otherwise healthy men, SHBG creeps upward with age. The Massachusetts Male Aging Study, one of the largest longitudinal datasets on male hormones, found that SHBG rose by about 1.2% per year between ages 39 and 70. Meanwhile, free testosterone dropped at roughly the same rate, and total testosterone declined more slowly because the rising SHBG partially masked the loss by holding more testosterone in a bound, inactive state.6The Journal of Clinical Endocrinology & Metabolism. Age, Disease, and Changing Sex Hormone Levels in Middle-Aged Men: Results of the Massachusetts Male Aging Study In men over 70, the pattern continues: a study of older Australian men found that SHBG kept increasing with age, free testosterone kept declining, yet total testosterone actually held steady or even rose slightly.7European Journal of Endocrinology. In men older than 70 years, total testosterone remains stable while free testosterone declines with age. The Health in Men Study
This is why age-related testosterone symptoms can be misleading if you look only at total testosterone. A 75-year-old man with a “normal” total testosterone reading may still have meaningfully low free testosterone because his SHBG has climbed high enough to soak up the available hormone.8PubMed. Testosterone and ill-health in aging men
Insulin, Body Weight, and Calorie Restriction
Insulin and SHBG move in opposite directions. A population study in Sweden found a strong inverse relationship between fasting insulin and SHBG levels: people with type 1 diabetes, who produce little or no insulin, had significantly higher SHBG than those without diabetes or those with type 2 diabetes (who tend to have high insulin from insulin resistance).9PubMed Central. Inverse association between serum insulin and sex hormone-binding globulin in a population survey in Sweden The implication is straightforward: anything that drops insulin levels tends to push SHBG up, and anything that raises insulin tends to pull SHBG down.
Calorie restriction is a dramatic illustration. Men who practiced long-term severe calorie restriction had significantly higher SHBG and lower free testosterone compared with men who maintained their weight through exercise or a standard Western diet. This held true even after accounting for differences in body fat, suggesting the calorie deficit itself, not just leanness, was driving the change.10PubMed Central. Long-term effects of calorie restriction on serum sex-hormone concentrations in men A systematic review looking across multiple calorie-restriction trials confirmed the pattern: SHBG rose in every study that measured it, regardless of how body composition changed.11Nutrition Reviews. Examining the effects of calorie restriction on testosterone concentrations in men: a systematic review and meta-analysis In one study of obese men undergoing caloric restriction, SHBG nearly doubled, climbing from roughly 22 to 42 nmol/L.12PubMed. Caloric restriction increases serum testosterone concentrations in obese male subjects by two distinct mechanisms
For men who are lean and eating very little, whether by choice, illness, or disordered eating, this mechanism can push SHBG high enough to slash free testosterone and produce real symptoms. It is a common and underappreciated contributor.
Growth Hormone Deficiency
Growth hormone (GH) appears to suppress SHBG production, so when GH is lacking, SHBG runs high. This was demonstrated clearly in boys with idiopathic hypopituitarism: their average SHBG was far above the normal range for their age, and after twelve months of GH replacement therapy, SHBG gradually came back down toward normal.13PubMed. High serum sex hormone-binding globulin (SHBG) and low serum non-SHBG-bound testosterone in boys with idiopathic hypopituitarism: effect of recombinant human growth hormone treatment In adults, GH deficiency is less common but not rare, and it should be on the differential when high SHBG cannot be explained by more obvious causes like thyroid disease or medications.
Medications That Raise SHBG
Certain drugs are well-known SHBG boosters. Liver enzyme-inducing anticonvulsants, particularly phenobarbital, phenytoin, and carbamazepine, increase SHBG production in both men and women with epilepsy. Over time, the elevated SHBG reduces the bioactivity of testosterone and estradiol, which can cause decreased sexual function in men and menstrual disturbances in women.14PubMed. Disorders of reproduction in patients with epilepsy: antiepileptic drug related mechanisms A retrospective study of men with raised SHBG found medications including carbamazepine and phenytoin as identifiable underlying causes.15Endocrine Abstracts. Raised sex hormone binding globulins levels in men: a retrospective observational study
Beyond anticonvulsants, the anti-estrogen tamoxifen and the phytoestrogen genistein (found in soy products) have both been shown to increase SHBG production and gene activity in liver cells, as has mitotane, a drug used in adrenal cancer.1PubMed. Sex hormone-binding globulin gene expression in the liver: drugs and the metabolic syndrome If you are on any of these medications and your SHBG is high, the drug is a likely explanation.
Genetic Variation
Your baseline SHBG level is partly inherited. Several common variants in and around the SHBG gene on chromosome 17 have consistent effects on blood levels. In a study of reproductive-age men, the variant rs1799941 raised SHBG by roughly 4.7 nmol/L per allele carried, while another variant, rs727428, lowered it by about 3.7 nmol/L per allele.16Journal of the Endocrine Society. Genetics of Sex Hormone-Binding Globulin and Testosterone Levels in Fertile and Infertile Men of Reproductive Age A more recent analysis put the effect sizes in percentage terms: men who were heterozygous or homozygous for rs1799941, rs6259, or rs727428 had SHBG concentrations roughly 11 to 23% higher than those with wild-type versions of those sites.17The Journal of Clinical Endocrinology & Metabolism. SHBG Gene Polymorphisms and Their Influence on Serum SHBG, Total and Free Testosterone Concentrations in Men
These genetic effects are large enough to push someone into the “high SHBG” range even when nothing else is wrong. They also have downstream health implications: the SHBG-raising allele of rs1799941 has been linked to a modestly reduced risk of type 2 diabetes, suggesting that genetically higher SHBG tracks with better metabolic health.18PubMed Central. Genetic evidence that raised sex hormone binding globulin (SHBG) levels reduce the risk of type 2 diabetes That said, genetics alone does not usually explain a sudden rise in SHBG. If your levels have climbed recently, the cause is more likely a change in thyroid function, weight, medication, or metabolic status than a variant you have carried your whole life.
Diet Composition
The ratio of protein to carbohydrate in your diet appears to influence SHBG independently of total calorie intake. An early crossover study of normal-weight men found that ten days on a high-carbohydrate diet produced noticeably higher SHBG (about 33 nmol/L) compared with a high-protein diet (about 23 nmol/L).19Life Sciences. Diet-hormone interactions: Protein/carbohydrate ratio alters reciprocally the plasma levels of testosterone and cortisol and their respective binding globulins in man More recently, a study of middle-aged men found that higher plant protein intake was associated with higher SHBG, with roughly 3 nmol/L difference between the highest and lowest intake groups. Animal protein showed the opposite pattern.20PubMed. Associations of dietary proteins with serum total testosterone and sex hormone-binding globulin concentrations in middle-aged men
These effects are modest compared with what thyroid disease or calorie restriction can do, and a randomized trial of overweight men found no difference in SHBG between high-protein and high-carbohydrate weight-loss diets over a longer follow-up period.21PLOS ONE. Long-Term Effects of a Randomised Controlled Trial Comparing High Protein or High Carbohydrate Weight Loss Diets on Testosterone, SHBG, Erectile and Urinary Function in Overweight and Obese Men Dietary macronutrient composition is probably a background influence rather than a major lever for most men, but it is worth knowing about if you are trying to account for a mildly elevated reading.
Kidney Disease and Hemodialysis
Chronic kidney disease adds another route to elevated SHBG. Men on hemodialysis had significantly higher SHBG than healthy controls (roughly 41 vs. 28 nmol/L on average), and biochemical hypogonadism was far more common in the hemodialysis group.22Nephrology Dialysis Transplantation. SEX HORMONE BINDING GLOBULIN (SHBG) SERUM LEVELS ARE INCREASED AND CORRELATE WITH INSULIN RESISTANCE IN MEN ON CHRONIC HEMODIALYSIS The reasons are not entirely clear, but likely involve altered hormone clearance, chronic inflammation, and disrupted metabolic signaling. Whatever the mechanism, kidney disease deserves a spot on the checklist of conditions that can elevate SHBG.
Environmental Chemical Exposures
Emerging evidence points to certain environmental pollutants as SHBG-raising agents, though the mechanisms are still being worked out. An analysis of U.S. adolescent and young adult males found that combined exposure to 17 endocrine-disrupting chemicals, including phthalates, collectively increased SHBG while decreasing bioactive testosterone, estradiol, and free androgen levels.23PubMed. Effects of exposure to 17 endocrine disrupting chemicals on sex steroid hormone levels in 12- to 19-year-old males in the United States A separate multi-country study of adult men found that persistent organohalogen pollutants (specifically CB-153 and p,p′-DDE, a breakdown product of the pesticide DDT) were each significantly and positively associated with higher SHBG levels.24Environmental Health Perspectives. Reproductive Hormone Levels in Men Exposed to Persistent Organohalogen Pollutants: A Study of Inuit and Three European Cohorts
The practical significance of these exposures for any individual is hard to pin down, since most people encounter these chemicals at low doses over long periods. But the pattern is consistent enough across studies that environmental contamination may be contributing a small upward push on SHBG in the general population, particularly in people with high occupational or dietary exposure to certain plasticizers or legacy pesticides.
Why the Measurement Itself Can Be Tricky
Before assuming a high SHBG reading reflects something biologically meaningful, it is worth knowing that SHBG assays are not perfectly standardized. A comparison of automated methods found that results from different assays could differ by up to 29% for the same blood sample, depending on the SHBG concentration.25PubMed. Evaluation of automated sex hormone binding globulin immunoassays Because many labs use the SHBG number to calculate free testosterone rather than measuring it directly, that variability can ripple through and change the clinical interpretation of your results.26PubMed. Variability in SHBG assays and the effect thereof on calculated estimates of free testosterone A single SHBG result that looks high on one platform might look upper-normal on another. Repeating the test or having free testosterone measured independently can help avoid over-reading a number that may partly reflect assay quirks.
When High SHBG Actually Matters Clinically
High SHBG does not automatically mean something is wrong. Some men carry gene variants that set their SHBG naturally higher and have no symptoms whatsoever. But when high SHBG pulls free testosterone low enough to cause fatigue, reduced libido, loss of muscle mass, or other androgen-deficiency symptoms, distinguishing between genuinely low free testosterone and a total testosterone that only looks adequate on paper becomes important. In men with borderline total testosterone and elevated SHBG, measuring or calculating free testosterone helps avoid both overdiagnosis and underdiagnosis of hypogonadism and guides appropriate decisions about hormone replacement therapy.27PubMed Central. Role of sex hormone-binding globulin in the free hormone hypothesis and the relevance of free testosterone in androgen physiology
The clinical approach is generally to look for the underlying cause rather than trying to lower SHBG directly. If hyperthyroidism is the driver, treating the thyroid brings SHBG down. If a medication is responsible, switching to an alternative drug (say, a non-enzyme-inducing anticonvulsant) can resolve the issue. If calorie restriction or very low body weight is the trigger, restoring adequate nutrition and energy balance usually normalizes things. In the absence of a treatable driver, or when SHBG elevation is largely genetic or age-related, the focus shifts to whether free testosterone is low enough to warrant treatment on its own.
SHBG May Do More Than Just Carry Hormones
For decades, SHBG was viewed as a passive shuttle, simply ferrying testosterone and estradiol through the blood and keeping them from reaching tissues. That picture has grown more complicated. Research has shown that SHBG can bind to receptors on cell surfaces and trigger intracellular signaling on its own, using a pathway that is independent of the classical hormone receptors inside cells.28PubMed. Sex hormone-binding globulin is synthesized in target cells Some investigators reported that SHBG binds to prostate cells and may influence their behavior, though the specific cell-surface receptors involved have not been fully identified or characterized.29Endocrine Reviews. A Reappraisal of Testosterone’s Binding in Circulation: Physiological and Clinical Implications Whether these signaling effects are large enough to matter in day-to-day health is an open question. But the finding that SHBG is not merely a hormone sponge adds another layer to why its level might have health implications beyond the simple arithmetic of free-testosterone calculation.
Exercise and SHBG
Exercise has a complex and sometimes counterintuitive relationship with SHBG. Intense endurance training over the course of a competitive season actually lowered SHBG in male athletes, with concentrations dropping from about 40 to 34 nmol/L between pre- and post-season measurements.30PubMed Central. Does Intense Endurance Workout Have an Impact on Serum Levels of Sex Hormones in Males? This goes against the assumption some people have that exercise raises SHBG. The direction of the effect probably depends on the type, intensity, and duration of training, as well as what is happening to body composition and energy balance at the same time. Men who exercise heavily while eating in a calorie deficit may see SHBG rise (because of the deficit) even as the exercise component pushes in the other direction. The net result depends on which influence is stronger.