SHBG Synthesis, Genetics & What Shifts It
The carrier protein that decides how much testosterone is free
Evidence grade 4 of 5, Strong. Read how the Atlas grades evidence.
The written rationale for this grade is still being prepared.
- FDA
- Not applicable (physiology)
Reference only. Not medical advice.
This is something to take to a clinician. The Atlas can tell you what is known about shbg synthesis, genetics & what shifts it in general. It cannot tell you what is happening in your body, and the difference matters most for exactly the symptoms that bring people to this page.
Sex hormone-binding globulin (SHBG) is a liver-made glycoprotein that binds ~40-45% of circulating testosterone tightly, leaving only the free (~2-3%) and loosely albumin-bound fractions biologically active. SHBG is the main reason total and free testosterone can diverge: anything that raises SHBG (aging, low calorie/low carb, hyperthyroidism, estrogen, liver disease) lowers free testosterone even if total is unchanged, while insulin resistance, obesity, and high insulin lower SHBG. Several 'free testosterone' supplements (tongkat ali, nettle root) claim to work by lowering or displacing SHBG.
Why two men with the same total T can have very different free T.
What it is invoked to explain
Claims this idea is used to support. Whether it supports them is the rest of the entry.
How it works
Hepatic SHBG production is regulated by HNF-4-alpha and is suppressed by insulin and by-products of de novo lipogenesis (which is why insulin resistance lowers SHBG) and increased by thyroid hormone and estrogen. Because only unbound testosterone enters cells, SHBG sets the free fraction. Genetic variants in the SHBG gene also produce stable inter-individual differences, partly explaining why men with identical total testosterone differ in symptoms.
What people get wrong
Often saidTotal testosterone tells you everything
ActuallySHBG can make total and free testosterone diverge widely. A 'normal' total with high SHBG can still mean low free testosterone and symptoms.
Who profits, and who pushes back
Nobody is named here yet, because we have not done that work on this entry. Read that as unfinished. Somebody almost certainly sells this, and somebody almost certainly disputes it. Assume both until we have checked.
At a glance
- Made in
- Liver
- Binds
- ~40-45% of testosterone (tightly)
- Raises SHBG
- Aging, low-calorie/low-carb, thyroid, estrogen
- Lowers SHBG
- Insulin/insulin resistance, obesity
What this entry does not yet cover
What follows is unfinished work on our side, not a finding about SHBG Synthesis, Genetics & What Shifts It. A short entry is not a safe entry.
- Timeline. We have not built the dated record of research and regulatory events.
- Cost and market. We have not documented what it sells for or who sells it.
- Supply chain. We have not mapped where it is made.
- Who uses it. We have not documented the user groups.
- What could change. No forward-looking summary yet.
- How it compares. We have not set it against the alternatives.
- Children and teenagers. We have not checked what is known about younger people.
- What can go wrong. We have not written the risk line for this one. Read the safety section below rather than treating its absence as reassurance.
- Where we land. We have not taken a position on this yet.
Sources
No sources recorded for this entry yet. Nothing on this page can be checked against a citation until that changes, so treat it as a summary awaiting its evidence.