Sex-hormone-binding globulin
Also called: SHBG
What it means
SHBG is a blood protein that binds testosterone and other sex hormones, controlling how much is "free" and active in your body.
Since SHBG rises with age, it can make total testosterone look fine even when the active, bone-relevant amount is actually low.
Sex-hormone-binding globulin, or SHBG, is a protein in your blood that binds to testosterone and other sex hormones. When testosterone is attached to SHBG, it isn't active in the body — only the free or loosely bound portion can actually act on tissues like bone. SHBG levels tend to rise with age, which matters more than most people realize.
Because SHBG rises as men get older, a man can have a total testosterone number that looks perfectly acceptable on a lab report while his free or bioavailable testosterone, the part his body can actually use, is low. This means total testosterone alone can be misleading. For a truer picture, checking SHBG alongside testosterone, using morning samples on two separate days, gives more reliable information than a single afternoon reading.
For bone health, this matters because male skeletons rely on oestradiol, a form of oestrogen made when testosterone is converted by an enzyme called aromatase. If SHBG is tying up testosterone, there's less available to convert. Any questions about testosterone levels, SHBG, or treatment decisions are best discussed with your prescriber, who can interpret your full picture.
How sure is this?
Graded Strong Clinical Evidence: Supported by multiple well-designed clinical studies in humans. Read each study with its grade in mind. One study is a piece of the picture, not the whole of it.
Where the Academy teaches it
This page is the short version. The lessons teach it in full, with the context around it and a quiz to lock it in.
Questions people ask about this
Yes. Men absolutely can get osteoporosis — in fact, roughly a third of all hip fractures happen in men, and men who fracture a hip have higher mortality afterward than women do. The decline is more gradual than the sharp drop women experience at menopause, but it's real and often overlooked.
Read the full answer →Related words
Testosterone is a male hormone that supports bone formation directly and indirectly, partly by being converted into…
Estrogen is a hormone that protects bone by keeping bone-removing cells in check. Falling estrogen, especially at…
An aromatase inhibitor is a medication that blocks the enzyme aromatase, which the body uses to make estrogen. It's…
Androgen deprivation therapy (ADT) is a prostate cancer treatment that lowers testosterone to very low levels. It's…
Hormone replacement therapy (HRT) replaces oestrogen, often with a progestin, after menopause and has been shown to…
Education only, not medical advice. Decisions about tests, medications and treatment belong with your own doctor. OsteoStrong does not diagnose, treat or cure any disease.
