SHBG Levels Explained: 6 Facts About Free Testosterone

SHBG levels in three numbers

Three numbers frame how SHBG levels behave. How fast they rise with age, how strongly low levels track with diabetes, and one simple step before the blood test.

Every figure on this page comes from a PubMed abstract, the Labcorp test page or MedlinePlus. The free testosterone chart is a calculation and is marked as such. This page is education, not a diagnosis.

What this guide covers

What is SHBG?

SHBG stands for sex hormone binding globulin. It is a protein made mainly by the liver. It binds testosterone and estradiol in the blood (MedlinePlus).

SHBG binds these hormones tightly and specifically. Albumin, another blood protein, binds them loosely. Together they decide how much hormone is free, the part that is usually considered active. A 2016 review called these proteins the primary gatekeepers of steroid action (PMID 27113851).

SHBG levels are not fixed. They change through life with metabolism, thyroid status and hormones, and they also depend on your genes (PMID 22531107).

How SHBG levels change free testosterone

Free testosterone is hard to measure directly. Labs often calculate it from total testosterone and SHBG. A 1999 study found that a calculated free testosterone matched the reference method closely, except in pregnancy (PMID 10523012).

The same study found the free androgen index and direct free testosterone immunoassays were not reliable. Both shifted with SHBG levels (PMID 10523012).

The chart shows the idea. Total testosterone stays at 600 ng/dL. Only SHBG changes. We calculated free testosterone with the Vermeulen equation for illustration.

A 2017 review adds a caution. It argued that the binding models behind these formulas are probably not fully accurate (PMID 28673039). Treat a calculated number as an estimate.

What is a normal SHBG level?

There is no single normal SHBG level. Each lab sets its own range. As one example, Labcorp lists these ranges for adult men.

The higher range after 49 fits the research. In a large study of men aged 40 to 70, SHBG levels rose about 1.6 percent per year of age (PMID 11836290). A Dutch population study also saw SHBG rise in men from age 45 onward (PMID 36038500).

What raises and lowers SHBG levels?

Many things move SHBG levels. The table lists the main ones, each with its source.

Thyroid is a good example. In men treated for an overactive thyroid, SHBG levels fell during treatment. In men treated for an underactive thyroid, SHBG rose (PMID 42684851).

Genes matter too. Men with 3 or more risk variants near the SHBG gene had a 6.5 times higher risk of low testosterone. That was compared with men with none (PMID 21998597).

What high SHBG can mean

High SHBG means less of your total testosterone is likely free for tissues to use (MedlinePlus). If total testosterone is borderline, free testosterone may be low even when total looks fine.

MedlinePlus lists liver disease, an overactive thyroid, some eating disorders, and low sex hormone production in men as possible causes. Older age also pushes SHBG levels up (PMID 11836290).

A review of men with type 2 diabetes found that high SHBG and low total testosterone were each linked with higher death rates. Men with total testosterone under 12 nmol/L and SHBG over 35 nmol/L had about 3 times the odds of death (PMID 31447413). This is an association in one group of patients.

Diet may play a small part. In 1,552 men, higher protein intake was linked with lower SHBG and higher fiber intake with higher SHBG. Calories, fat and carbohydrate were not linked (PMID 10634401).

What low SHBG can mean

Low SHBG means more of your total testosterone is likely free (MedlinePlus). That sounds good, but low SHBG is often a sign of how your metabolism is doing.

MedlinePlus lists an underactive thyroid, type 2 diabetes or insulin resistance, obesity, Cushing syndrome and overuse of anabolic steroids as causes.

In a large study, men with the highest SHBG had about one tenth the odds of type 2 diabetes of men with the lowest SHBG. Gene data suggested SHBG may play a causal role (PMID 19657112).

A pooled analysis of 20 studies found that each quarter lower SHBG raised the odds of metabolic syndrome by 1.73 times (PMID 25019163). People with fatty liver disease also had lower SHBG levels (PMID 28425408).

SHBG levels on TRT and on steroids

Androgens push SHBG levels down. In one test, 3 days of oral stanozolol cut SHBG to about 52 percent of the starting value in healthy controls (PMID 2723028). Doctors once used this drop as a test of androgen sensitivity.

MedlinePlus lists overuse of anabolic steroids as a cause of low SHBG. That is why SHBG levels on a cycle are often very low. For cycle effects see TRT vs steroid cycles.

On TRT, SHBG levels matter for reading labs. The Endocrine Society advises measuring free testosterone when total testosterone is near the lower limit or when a condition alters SHBG (PMID 29562364).

Can you change your SHBG levels?

Usually by treating the cause, not by chasing the number. Here is what the research shows.

Weight loss. A 2026 umbrella review found that weight loss raised SHBG levels in men with obesity. Bariatric surgery raised SHBG by up to 21.22 nmol/L. Diet changes helped less (PMID 41167564).

Thyroid treatment. Treating an overactive or underactive thyroid moved SHBG levels back toward normal in men (PMID 42684851).

Diet. Protein intake was linked with lower SHBG, and fiber with higher SHBG, in one large study (PMID 10634401). That was an observational link, not a trial.

Supplements. We did not find trial evidence strong enough to cite for any supplement that reliably changes SHBG in men. Treat such claims with care.

How to test your SHBG levels properly

MedlinePlus says no special preparation is needed for the SHBG test itself, but you should not stop any medicine unless your doctor says so.

Six facts about SHBG and free testosterone

1. SHBG is a liver protein that holds testosterone. It decides how much is free (PMID 27113851).

2. Calculated free testosterone beats the free androgen index. (PMID 10523012).

3. SHBG levels rise with age in men. About 1.6 percent per year (PMID 11836290).

4. Low SHBG is a metabolic warning sign. Linked with diabetes and metabolic syndrome (PMID 19657112, PMID 25019163).

5. Androgens lower SHBG. Stanozolol cut it to about half in days (PMID 2723028).

6. Thyroid and weight move SHBG. Treating them changes the number (PMID 42684851, PMID 41167564).