Hormones and performance
How to Increase Free Testosterone: Lowering High SHBG
Reviewed by a qualified clinician · analysed at UKAS-accredited UK labs (ISO 15189)
Last reviewed June 202612 min read
Every Helvy guide is written by our health editors, then checked by a qualified clinician before it goes live and re-checked as the science moves. We name clinical roles, not individuals, until each reviewer has agreed to be credited publicly. This is wellness guidance to help you understand your own data, not a diagnosis.
Quick answer
You cannot raise free testosterone directly, but you can free up more of the testosterone you already make by lowering high SHBG. High SHBG is usually driven by ageing, an underactive calorie intake, very low-carb dieting, an overactive thyroid, or liver strain. Address the driver, retest on a morning fasted sample, and interpret the result with a qualified clinician.
Your total testosterone came back at 18 nmol/L. Comfortably normal. Yet the symptoms that sent you for the test in the first place, flat energy, slower recovery, low drive, have not shifted. The number says you are fine. Your body disagrees.
This is one of the most common and least explained results in men's health. The answer is rarely the total figure. It is how much of that testosterone is actually free to do its job, and the single protein that decides it: sex hormone-binding globulin (SHBG). This guide explains what genuinely raises the free fraction, what is marketing noise, and how to measure it properly. It is based on 2023 BSSM guidelines and peer-reviewed research.
By the Helvy Medical Team · Reviewed by a qualified clinician · 12 min read
1. Free vs total testosterone, in one minute
Total testosterone counts every molecule in your blood. But most of it is bound and biologically silent. Only the unbound, “free” fraction (roughly 2 to 3 percent) can enter a cell and act. The rest is held by two proteins: about 60 to 70 percent locked tightly to SHBG, and 30 to 40 percent held loosely by albumin.
Free testosterone, plus the loosely-held albumin fraction, makes up your bioavailabletestosterone, the part that reaches tissue. The BSSM treats a calculated free testosterone below 0.225 nmol/L as low, regardless of where the total sits. So two men with an identical total of 18 nmol/L can have completely different biology: one symptom-free, the other running on far less active hormone.
For the full breakdown of what free testosterone is and the normal ranges, see our guide to free testosterone vs total. This guide is about the next question: if your free fraction is low, what do you actually do about it?
2. SHBG is the dial that sets your free testosterone
Think of SHBG as a sponge in your bloodstream. The more SHBG you have, the more testosterone it soaks up and holds inactive, leaving less free to work. Lower the SHBG and the same total testosterone releases more free hormone. This is why you cannot meaningfully “increase free testosterone” as a standalone target. You change it by changing SHBG, or by raising total production (covered in our guide to raising testosterone naturally).
A worked example. A man with total testosterone of 18 nmol/L and SHBG of 25 nmol/L has a healthy free fraction. The same 18 nmol/L total with SHBG of 70 nmol/L means most of that testosterone is bound and unavailable. His total looks reassuring; his free testosterone can sit in genuinely deficient territory. This is exactly the “normal result, low symptoms” pattern.
The same logic runs in reverse for women, where the free androgen index (FAI) uses the testosterone-to-SHBG ratio to estimate active androgen. High and low SHBG both matter, which is the theme of the rest of this guide.
3. Why “low free testosterone” usually means high SHBG
SHBG climbs with age. A 2025 study of healthy men without obesity found SHBG rose by 0.6 nmol/L per year of age, averaging 29 nmol/L in men aged 18 to 29 and rising to 41 nmol/L past 50. That steady rise is why free testosterone falls faster than total testosterone across the lifespan.
The Baltimore Longitudinal Study of Aging put numbers on it: bioavailable testosterone declines in a straight line with age, and steeper than total testosterone does, because rising SHBG mediates the gap. In plainer terms, an older man can keep a respectable total reading while his usable testosterone quietly drops. The total reassures; the free fraction tells the real story.
Age is not the only cause of a high reading, and several of the others are modifiable. That is where the practical work begins.
4. What raises SHBG (and lowers your free testosterone)
If your free fraction is low because SHBG is high, the useful question is which of these is driving it. Several are within your control.
| DRIVER | WHY IT RAISES SHBG |
|---|---|
| Ageing | SHBG rises around 0.6 nmol/L per year. Largely unavoidable, but it sets the baseline everything else stacks on. |
| Under-eating | Sustained calorie deficits and low body weight push SHBG up. The body reads scarcity as a reason to bind hormones away. |
| Very low-carb diets | Prolonged ketogenic or very low-carbohydrate eating is associated with higher SHBG in some people, plausibly via the same energy-restriction signal. |
| Overactive thyroid | Excess thyroid hormone directly stimulates the liver to make more SHBG. Hyperthyroidism is a classic and treatable cause. |
| Liver strain | SHBG is made in the liver. Chronic alcohol load and some liver conditions can push production up. |
| Oestrogen and some medicines | Higher oestrogen exposure, anticonvulsants and certain other drugs raise SHBG. Worth a medication review with your prescriber. |
Notice the pattern: ageing aside, the biggest movers are energy intake, thyroid function and the liver. None of those respond to a “free testosterone booster.” They respond to fixing the cause.
5. What genuinely lowers high SHBG
There is no supplement that reliably lowers SHBG. What works is removing whatever is pushing it up. These are the levers with real mechanisms behind them, listed by how often they matter.
EAT ENOUGH, ESPECIALLY IF YOU TRAIN
If you are dieting hard, training a lot, or both, a chronic energy deficit is one of the most common reversible reasons for a high SHBG. Bringing calories back to maintenance, with enough carbohydrate to fuel training, often brings SHBG down over weeks. This is the opposite of the usual fitness advice, which is exactly why lean, disciplined men are the ones who get caught out.
CHECK YOUR THYROID
An overactive thyroid is a direct, treatable cause of high SHBG. If you have a low or suppressed TSH alongside symptoms like a racing heart, heat intolerance or unintended weight loss, that is worth investigating with your GP. Correcting the thyroid problem typically normalises SHBG.
MODERATE ALCOHOL, PROTECT THE LIVER
Because SHBG is produced in the liver, persistent heavy drinking can push it up while also suppressing testosterone production directly. Cutting back is one of the simpler high-yield changes, and it shows up in your liver markers too.
REVIEW YOUR MEDICATIONS
Anticonvulsants, oral oestrogens and a handful of other prescriptions raise SHBG. Never stop a prescribed medicine on your own, but if you are on one of these and your free testosterone is low, it is a reasonable conversation to have with the prescriber.
BE SCEPTICAL OF SHBG “LOWERING” SUPPLEMENTS
Boron, stinging nettle root and similar supplements are widely sold for this. The human evidence is small, short and inconsistent, and none carries an approved health claim in Great Britain for SHBG or testosterone. They are not a substitute for finding and fixing the actual driver. If you want to try one, treat it as an experiment and measure before and after rather than assume it worked.
The honest summary: a high SHBG is a signal, not a disease. Most of the time it is pointing at age, an energy deficit, the thyroid or the liver. Treat what it is pointing at and the free fraction usually takes care of itself.
6. The insulin paradox: a low SHBG is not a win
It would be easy to read this guide and conclude that less SHBG is always better. It is not. Insulin directly suppresses the liver's production of SHBG, so insulin resistance and excess body fat tend to drive SHBG down. The 2025 study above found insulin resistance was inversely associated with SHBG, and that both SHBG and total testosterone fell as insulin resistance rose.
So a low SHBG often travels with insulin resistance, a fatty liver and a low total testosterone. Your free fraction might look adequate on paper, but the underlying metabolic picture is the problem. This is the mirror image of the lean older man with high SHBG, and it is why SHBG always needs reading alongside total testosterone, insulin resistance markers and body composition, never in isolation.
The takeaway is balance, not minimisation. You are aiming for an SHBG that is appropriate for your age and metabolic health, with a free testosterone in a healthy range, not the lowest SHBG you can engineer.
7. How to measure your free testosterone properly
Most labs do not measure free testosterone directly. They calculate it from total testosterone, SHBG and albumin using a validated equation (the Vermeulen calculation). That means a free testosterone result is only as good as the SHBG and albumin it is built from, so all three need to be on the same blood draw.
To get a result worth acting on:
- Test in the morning, fasted, ideally before 10am, when testosterone peaks. See our guide to the best time to test testosterone.
- Measure total testosterone, SHBG and albumin together so free testosterone can be calculated accurately.
- Repeat a low or borderline result on a second morning sample. A single reading is never enough for a decision.
- Add LH, FSH and prolactin if the free fraction is low, to show whether the issue is binding, production or the pituitary.
Our Complete Male Hormones panel measures testosterone, free testosterone, SHBG, albumin, the free androgen index, LH, FSH, prolactin and DHEA-S on one finger-prick sample, which is the full set you need to interpret a free testosterone result rather than guess at it. Your results suggest where to look; a qualified clinician should interpret them.
Frequently asked questions
Can you increase free testosterone naturally?
Indirectly, yes. You cannot target the free fraction on its own, but you can free up more of the testosterone you already make by lowering a high SHBG, usually by eating enough, fuelling training with adequate carbohydrate, moderating alcohol and correcting an overactive thyroid. You can also raise total production through sleep, strength training and losing excess body fat.
What is a normal SHBG level for a man?
Reference ranges vary by lab and rise with age. One 2025 study of healthy men proposed roughly 16 to 57 nmol/L for men under 50 and 20 to 82 nmol/L for those aged 50 and over. The number only means something alongside your total testosterone, because the same SHBG can be fine for one man and limiting for another.
Does a low-carb or keto diet lower testosterone?
It can raise SHBG in some people, which lowers the free fraction even if total testosterone holds. The effect seems tied to sustained energy restriction more than carbohydrate itself. If you eat very low-carb, feel flat and have a high SHBG, trialling more carbohydrate and overall calories at maintenance for a few weeks, then retesting, is a reasonable experiment.
Do supplements like boron actually lower SHBG?
The human evidence for boron, stinging nettle and similar supplements is small, short-term and inconsistent, and none holds an approved health claim in Great Britain for SHBG or testosterone. They are not a reliable fix and should not replace finding the real driver. If you try one, measure SHBG and free testosterone before and after rather than assume an effect.
My total testosterone is normal but I feel terrible. Why?
A common explanation is a high SHBG holding too much of your testosterone inactive, so your free fraction is low despite a reassuring total. Other causes worth checking include thyroid function, iron, vitamin D and sleep. The way to tell is to measure total testosterone, SHBG and albumin together and calculate free testosterone, then discuss the pattern with a qualified clinician.
Is a very low SHBG good?
Not necessarily. A low SHBG often accompanies insulin resistance, excess body fat and a fatty liver, and frequently travels with a low total testosterone. It is best read alongside your total testosterone and metabolic markers rather than treated as a win on its own.
See how much of your testosterone is actually free
Our Complete Male Hormones panel (£119) measures total and free testosterone, SHBG, albumin, the free androgen index, LH, FSH, prolactin and DHEA-S. Home finger-prick kit, results in 5 working days, from UKAS-accredited UK laboratories.
Medical disclaimer: This content is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Reference ranges cited here are based on published research and BSSM guidance and may differ from those used by your local NHS laboratory. Do not change medication, supplementation, diet or training based solely on this article; consult your GP or a qualified healthcare professional. All Helvy blood tests are processed by UKAS-accredited UK laboratories to ISO 15189.
Last updated: June 2026 · By Helvy · Medically analysed at UKAS-accredited UK laboratories
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