Low SHBG and Testosterone: What It Means and How to Fix It

Why SHBG Is the Missing Piece in Your Testosterone Workup

Most men who get a testosterone test only look at total testosterone. But total testosterone tells you almost nothing without knowing your SHBG level. SHBG — sex hormone-binding globulin — is a protein that binds to testosterone in the bloodstream, rendering it unavailable to your cells. The testosterone that matters is the free fraction not bound to SHBG.

You can have "normal" total testosterone of 600 ng/dL but low free testosterone if SHBG is high. Conversely, you can have below-average total testosterone and feel great if SHBG is low. Understanding this distinction is the difference between optimizing your hormones and chasing a number.

What SHBG Actually Does

SHBG is produced primarily in the liver. It binds to testosterone (and estradiol) with high affinity, creating a reservoir of hormone that is biologically inactive. Only unbound free testosterone — roughly 1-3% of total — can enter cells and activate androgen receptors.

Albumin also binds testosterone, but more loosely. The testosterone bound to albumin can be released and used by tissues; it's classified as "bioavailable." So the complete picture is:

• Total testosterone: Everything — bound + free
• Free testosterone: Unbound, maximally active (~1-3%)
• Bioavailable testosterone: Free + albumin-bound (~30-40%)
• SHBG-bound testosterone: Biologically inactive

When labs report "free testosterone," they're measuring the most relevant clinical fraction. Most standard lipid panels don't include it — you have to specifically request it, along with SHBG.

Normal and Abnormal SHBG Ranges

Normal SHBG for adult men is approximately 10-57 nmol/L, but like most hormone ranges, "normal" is wide and doesn't tell you where you should be for optimal function.

Low SHBG (under 20 nmol/L): Often seen with insulin resistance, type 2 diabetes, metabolic syndrome, obesity, and hypothyroidism. Exogenous testosterone (TRT) also suppresses SHBG significantly.

High SHBG (above 50-60 nmol/L): Common with aging, hyperthyroidism, liver disease, low-fat diets, and use of some medications (anticonvulsants, certain estrogens). High SHBG means even adequate total testosterone results in low free testosterone.

Low SHBG: What It Actually Means

Low SHBG is a double-edged sword. On one hand, more free testosterone is available. On the other, low SHBG is often a marker of underlying metabolic dysfunction — particularly insulin resistance.

The liver produces less SHBG in the presence of high insulin. So low SHBG is often a downstream signal that insulin is elevated and metabolism is dysregulated. This is why low SHBG is associated with increased risk of:

• Type 2 diabetes
• Non-alcoholic fatty liver disease
• Cardiovascular disease
• Polycystic ovary syndrome (in women)

Low SHBG with normal total testosterone may mean free testosterone is adequate, but you shouldn't celebrate without also assessing insulin sensitivity, fasting glucose, and metabolic markers.

High SHBG: The More Common Clinical Problem

More often in clinical practice, high SHBG is the problem that needs addressing. Men with high SHBG report classic symptoms of low testosterone — fatigue, low libido, loss of muscle, increased fat — even though their total testosterone looks "fine."

A 50-year-old with total testosterone of 500 ng/dL and SHBG of 70 nmol/L has free testosterone in the hypogonadal range. He will feel terrible and benefit from treatment. Meanwhile, a 35-year-old with total testosterone of 350 ng/dL and SHBG of 15 nmol/L has excellent free testosterone and may feel fine.

Always calculate free testosterone before making any treatment decisions.

How to Calculate Free Testosterone

If your lab doesn't directly measure free testosterone (many use an unreliable equilibrium dialysis-derived approximation), you can calculate it:

Vermeulen formula: Requires total testosterone, SHBG, and albumin. Multiple online calculators exist (search "free testosterone calculator Vermeulen"). Enter your values and you'll get an estimated free testosterone in pg/mL or nmol/L.

Reference ranges (Vermeulen calculation): - Optimal for men under 50: >150 pg/mL - Optimal for men 50+: >100 pg/mL - Low: <50 pg/mL - Severely deficient: <30 pg/mL

These are rough guides; symptoms matter as much as numbers.

Strategies to Lower SHBG Naturally

If you have high SHBG and want to increase free testosterone without TRT:

Strength training: Resistance training reduces SHBG — likely via insulin-sensitizing effects. Heavy compound movements (squat, deadlift, press) are most effective. Consistent training over months produces meaningful SHBG reduction.

Reduce alcohol: Alcohol increases SHBG by affecting liver function. Even moderate drinking can elevate SHBG over time.

Reduce soy intake: Phytoestrogens in soy can increase SHBG in some men. The effect size is modest but worth testing if SHBG is borderline high.

Improve insulin sensitivity: Since SHBG is liver-derived and inversely correlated with insulin, anything that improves insulin sensitivity reduces SHBG. Weight loss, low-carb or Mediterranean diet, regular exercise, and reduced ultra-processed food all help.

Boron: Some research supports 6-10mg daily boron supplementation reducing SHBG by 20-30%. Mechanism is unclear; evidence is modest but safe to try.

Zinc: Deficiency is associated with elevated SHBG. Ensure adequate intake through diet or supplementation (15-30mg zinc/day).

When to Consider TRT Despite Low SHBG

TRT suppresses SHBG further — sometimes dramatically. Men with already-low SHBG who start TRT may see free testosterone skyrocket, which can increase conversion to estradiol and require careful management with aromatase inhibitors.

However, if you have genuine hypogonadal symptoms — fatigue, loss of morning erections, depression, significant body composition changes — and your free testosterone is confirmed low, treatment is warranted regardless of SHBG status. The risk-benefit calculation doesn't change based on SHBG alone.

At Marrow, we measure total testosterone, SHBG, free testosterone, estradiol, LH, FSH, and complete metabolic panel at intake. We're not treating numbers — we're treating your symptoms, backed by comprehensive labs that give us the full picture.

Monitoring on TRT

If you're already on testosterone replacement, SHBG should be measured every 3-6 months. TRT dramatically lowers SHBG, which is expected. The important metric is free testosterone — target ranges vary by individual, but most men feel optimal with free testosterone in the upper quarter of the normal range (150-250 pg/mL on equilibrium dialysis).

If free testosterone is too high relative to symptoms, your dose may need reduction. If it's still low despite adequate total testosterone, very low SHBG may mean you need a lower, more frequent dosing protocol rather than a higher dose.

Understanding SHBG transforms your testosterone picture from a single data point into a complete story. Your Marrow physician reviews all of these markers together — because optimizing hormones requires understanding the full system, not just chasing a number.