What Is Sex Hormone–Binding Globulin (SHBG)?

Sex hormone–binding globulin (SHBG) is a protein made mainly in the liver. It binds strongly to key sex hormones like testosterone, dihydrotestosterone (DHT), and estradiol. By doing so, SHBG controls how much of these hormones stay “free” (unbound) and biologically active in the body. Think of SHBG as a gatekeeper: it influences how much hormone is available to tissues in both men and women.

In US labs, SHBG is measured in nmol/L. Typical adult reference ranges include:

• Men: Often around 13–89 nmol/L (e.g., Mayo Clinic Laboratories: ≥18 years, 13.3–89.5 nmol/L; Labcorp: 20–49 years, 16.5–55.9 nmol/L; ranges vary by age, lab, and assay).
• Premenopausal women: Around 18–135 nmol/L (e.g., Mayo Clinic: 18–46 years, 18.2–135.5 nmol/L; Labcorp: 20–49 years, 24.6–122 nmol/L).

Optimal levels depend on your total hormone levels and symptoms—not just fitting into population averages.

SHBG, Sex Differences, and DHEA Influence

High SHBG ties up more sex steroids, reducing the free fraction—even if total levels look normal. In women on combined oral contraceptives, the ethinyl estradiol component boosts SHBG significantly, often dropping free testosterone and contributing to issues like lower libido or vaginal dryness.

In men, elevated SHBG can cause androgen deficiency symptoms despite normal total testosterone, as less hormone reaches target tissues.

Adrenal hormones like DHEA and DHEA-S add to the androgen pool. Excess adrenal androgens (common in some PCOS cases) can suppress SHBG through increased androgen signaling. Age-related DHEA decline often links to rising SHBG and lower free androgens.

Major Regulators: Hormones, Insulin, and Cortisol

Estrogens ramp up SHBG production, while androgens lower it—this balance intensifies with oral contraceptives (estrogen-driven rise) or hyperandrogenic conditions (androgen-driven drop).

Thyroid function plays a big role too: hyperthyroidism raises SHBG, hypothyroidism lowers it through effects on liver gene regulation.

Metabolic factors are key. High insulin from resistance or obesity suppresses SHBG, tying low levels to metabolic syndrome, type 2 diabetes, and cardiovascular risk. Chronic high cortisol (from stress) disrupts gonadal function and shifts binding across proteins like SHBG, albumin, and corticosteroid-binding globulin—often reducing free androgens.

SHBG as a Marker of Metabolic and Heart Risk

Low SHBG reliably predicts insulin resistance, type 2 diabetes, and cardiovascular events in large studies of men and women—independent of total sex hormones. In men, it signals visceral fat and cardiometabolic progression; in postmenopausal women, it links to central obesity and dyslipidemia.

Very high SHBG calls for checking hyperthyroidism, undernutrition, excess estrogen, or clinically low free hormones affecting muscle, mood, or sexual health.

Oral Contraceptives, Dyspareunia, and Sexual Function

Combined oral contraceptives can raise SHBG several-fold (sometimes persisting months after stopping in sensitive women). Paired with suppressed ovarian androgens, this slashes free testosterone, promoting vulvovaginal dryness, poor lubrication, and painful intercourse (dyspareunia).

For those with pain during sex or low desire—especially after starting the pill—SHBG offers context beyond total hormones. Test alongside free testosterone, estradiol, and DHEA-S.

Nutraceuticals: Nettles, Boron, and Practical Modulation

Address root causes first: boost insulin sensitivity, cut excess body fat, optimize thyroid function, improve sleep, and support liver health. These steps reliably help normalize SHBG.

Stinging nettle root contains lignans that bind SHBG in lab studies, potentially freeing up testosterone—though solid human trials on SHBG changes and outcomes are limited.

Boron (typically 6–10 mg/day) shows promise in small studies (mostly men): it can lower SHBG, raise free testosterone, and reduce estradiol short-term. Data in women and long-term effects are sparse.

Clinical Takeaways

SHBG weaves together endocrine and metabolic signals. Low levels flag the need for metabolic evaluation; high levels prompt reviews of thyroid, estrogen, adrenals (including DHEA), nutrition, and sexual health. Focus on foundational lifestyle changes first—use nutraceuticals like nettle or boron thoughtfully as supports. Always interpret in personal context for best results.