Sex hormone-binding globulin (SHBG)

On this page

What is SHBG?
Where is SHBG produced?
Function of SHBG
SHBG and fertility
Normal SHBG levels
Causes of high SHBG
Causes of low SHBG
When and how to test SHBG
SHBG in traditional Chinese medicine
Acupuncture and SHBG
Chinese herbal medicine and SHBG
Diet and lifestyle
Related pages

1. What is SHBG?

Sex hormone-binding globulin (SHBG) is a glycoprotein produced primarily by the liver. It is a carrier protein that binds tightly to testosterone, dihydrotestosterone (DHT) and (less strongly) to oestradiol, transporting them in the bloodstream. Hormones that are bound to SHBG are inactive — only the small fraction of "free" hormone (typically 1–3% of total testosterone) is biologically available to bind to receptors and exert effects.

SHBG is therefore a critical regulator of how much active testosterone and oestradiol the body's tissues actually "see". Changes in SHBG can have major effects on fertility, even when total hormone levels are within reference ranges.

Reference ranges vary from country to country and between laboratories. Always interpret your own result against the reference range provided by the laboratory that performed your test.

2. Where is SHBG produced?

SHBG is produced almost entirely by hepatocytes (liver cells). Its production is increased by oestrogens and thyroid hormones, and reduced by insulin, androgens and obesity. Small amounts of SHBG are also produced by the brain, uterus, testes and placenta.

3. Function of SHBG

The main functions of SHBG are:

Binding and transporting testosterone, DHT and oestradiol in the blood.
Regulating the bioavailability of these hormones — high SHBG means less free hormone, low SHBG means more free hormone.
Buffering rapid changes in hormone production.
Acting as a signalling molecule in its own right via SHBG receptors on some tissues.

4. SHBG and fertility

SHBG plays an important role in fertility through its effect on free testosterone:

Low SHBG means more free testosterone — important for follicle growth in modest amounts but problematic in PCOS where it drives androgen excess.
High SHBG means less free testosterone — can affect follicle growth and reduce libido. Common in hyperthyroidism and with combined oral contraceptive use.
SHBG is one of the body's natural mechanisms for balancing hormones — when oestrogens rise, SHBG rises, reducing free testosterone; when androgens rise, SHBG falls, exposing more free oestrogen.

5. Normal SHBG levels

The typical reference range for SHBG in women is approximately 18–114 nmol/L on day 3 of the menstrual cycle. Reference ranges vary from country to country and between laboratories.

6. Causes of high SHBG

High SHBG is caused by:

Hyperthyroidism — thyroid hormones strongly stimulate SHBG production.
Oestrogen therapy and oral contraceptives — oestrogens increase SHBG.
Pregnancy — markedly raised SHBG.
Liver disease — variable; chronic liver disease may raise or lower SHBG.
Anorexia and severe undereating.
Caffeine consumption — research has shown that caffeine can raise SHBG, reducing free testosterone needed for follicle growth.
Vegetarian and vegan diets — research has shown higher SHBG and lower free testosterone, which can affect egg growth.

7. Causes of low SHBG

Low SHBG is caused by:

Insulin resistance and PCOS — high insulin suppresses SHBG, leading to high free testosterone.
Hypothyroidism — low thyroid hormones reduce SHBG.
Obesity — particularly central obesity.
Cushing's syndrome.
High androgen levels from any cause.
Long-term use of synthetic glucocorticoids.

8. When and how to test SHBG

SHBG is usually measured on day 2 or 3 of the menstrual cycle as part of a hormone panel — particularly in the investigation of PCOS, thyroid-related fertility problems and unexplained infertility. SHBG is most useful when interpreted alongside total testosterone, allowing the calculation of the free androgen index (FAI).

Reference ranges vary from country to country. Always interpret your own result against the laboratory's reference range and discuss it with your doctor.

9. SHBG in traditional Chinese medicine

In traditional Chinese medicine, the liver is considered the central organ governing the regulation of menstrual hormones. The liver's role in producing SHBG and clearing oestrogens fits closely with the TCM understanding of the Liver's role in storing and regulating Blood, and ensuring the smooth flow of Qi and hormones. Imbalances in SHBG often reflect Liver Qi stagnation, Liver Blood deficiency or Liver Heat, depending on the pattern.

10. Acupuncture and SHBG

By regulating liver function, reducing insulin resistance, supporting thyroid function and lowering cortisol, acupuncture indirectly supports healthy SHBG levels. In PCOS, acupuncture has been shown to improve insulin sensitivity, which raises SHBG and reduces free testosterone — one of the mechanisms by which it improves PCOS-related infertility.

11. Chinese herbal medicine and SHBG

Liver-supportive Chinese herbal formulae such as Xiao Yao San, Long Dan Xie Gan Tang and Yi Guan Jian help regulate liver function and indirectly support healthy SHBG. For PCOS with low SHBG and insulin resistance, Cang Fu Dao Tan Tang and modifications are commonly used. Treatment is always individualised after a full TCM assessment.

12. Diet and lifestyle

To support healthy SHBG levels:

Address insulin resistance — reduce refined sugar and gluten, exercise regularly, consider myo-inositol.
Maintain a healthy weight (waist:hip ratio below 0.8 in women).
Reduce caffeine — caffeine raises SHBG and reduces free testosterone needed for follicle growth.
Eat a varied diet with adequate protein — vegetarians and vegans need to be particularly careful.
Address thyroid function — both hypo- and hyperthyroidism affect SHBG.
Limit alcohol — alcohol affects liver function and SHBG production.
Reduce psychological stress.