SHBG - Do you know the importance of adequate levels?

Sex hormone-binding globulin (SHBG) is a protein that affects the function of certain sex hormones, including testosterone and estrogen (1,2). It is primarily produced in the liver (1).

In summary, SHBG binds to specific sex hormones, removing them from direct circulation in the body (1).

In the bloodstream, sex hormones can be found in two forms: free and bound. Hormones can bind to different molecules. In the case of testosterone and estrogen, one of these molecules is SHBG. Another is the protein albumin (1,2).

When a sex hormone is free or bound to albumin, the hormone is considered bioavailable (1). This means it can enter tissue and produce a biological effect.

Conversely, when bound to SHBG, the sex hormone is essentially inactive and has minimal—or no—biological impact on the body until its release (1).

In women and individuals with female reproductive organs, the vast majority of testosterone and estradiol in the blood is bound to SHBG and other proteins and is not bioavailable—only about 2% of these sex hormones are free to bind to receptors and produce an impact on the body (3,4).

SHBG can also release hormones into specific tissues and possibly directly within cells (1,2). This binding produces an effect on both sex hormones and SHBG. Sex hormones bound to SHBG do not affect body function until released, and sex hormones bound to SHBG can affect how well SHBG binds to its own receptor (1).

(Receptors are like locks, and only certain keys—such as hormones or SHBG—can open them.)

Low SHBG levels: how do they affect the body? Effects & associations

Since SHBG binds to sex hormones, its relative level can affect the levels of sex hormones available for use by the body—thereby affecting the processes that sex hormones regulate.

For example, when SHBG levels are relatively low in women, testosterone levels can become atypically high, causing side effects such as hirsutism and acne (2).

There may also be a relationship between SHBG, testosterone, and libido (sexual desire).

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