- SHBG is a carrier protein that binds to testosterone, controlling how much is available to your tissues.
- High SHBG reduces free testosterone even if total testosterone is normal; low SHBG increases it.
- SHBG reflects metabolic health: it rises with high cardio volume and falls with resistance training and calorie adequacy.
- Interpret SHBG alongside total and free testosterone, not in isolation.
- SHBG is stable; test annually unless your training or health markers shift significantly.
Quick Answer
Sex Hormone Binding Globulin (SHBG) is a protein in your blood that acts like a taxi service for testosterone and oestrogen. It carries these hormones, but while they're bound to SHBG, they can't do their job. The amount of SHBG you produce directly affects how much hormone is actually available to your muscles, brain, and organs. This matters because your total testosterone result can look normal, but if your SHBG is very high, most of that testosterone is locked up and unavailable: leaving you with low free testosterone despite a respectable total.
Why Athletes and Active People Care
If you're training seriously, your SHBG matters because it directly influences recovery, muscle adaptation, and energy availability.
Endurance training and SHBG: Long-distance runners and cyclists often see higher SHBG, particularly at high training volumes.[5] This isn't inherently bad: it's an adaptation: but it means less free testosterone is circulating, which can slow muscle growth and recovery if you're also doing strength work.
Metabolic health: SHBG is strongly linked to insulin sensitivity.[4] People with better metabolic health tend to have lower (more optimal) SHBG levels. Conversely, high SHBG sometimes flags insulin resistance or metabolic stress.
Total vs. free testosterone: This is the critical distinction. You can have a total testosterone of 15 nmol/L (respectable) but if SHBG is 70 nmol/L, your free testosterone drops to around 0.5 nmol/L: very low. You won't see that in the total number alone.
The Range Explained
RCPA reference ranges for adult men are approximately 15–70 nmol/L, depending on assay and lab.[1] For women, ranges are typically lower, around 10–50 nmol/L. These are broad ranges because SHBG naturally varies with training, diet, and metabolic state.
| SHBG Result | What it may indicate |
|---|---|
| Lower (15–30 nmol/L) | Higher free testosterone; good metabolic health; resistance training adaptation |
| Mid-range (30–50 nmol/L) | Optimal balance of free and bound hormone; typical for active people |
| Higher (50–70+ nmol/L) | More hormone bound; common in endurance athletes; lower free hormone availability |
The range itself is normal, but the meaning depends on your training and your total testosterone level. A marathon runner with SHBG of 65 nmol/L is expected. A powerlifter with the same result might warrant investigation.
How to Interpret Your Results
Always look at SHBG alongside total testosterone and, ideally, calculated or direct free testosterone.
Scenario 1: Normal SHBG, normal total testosterone You likely have adequate free testosterone. Recovery and hormonal health are probably fine.
Scenario 2: High SHBG, normal total testosterone Most of your testosterone is bound and unavailable. You may experience sluggish recovery, low libido, or slow muscle gain despite training hard. This is common in high-volume endurance athletes and warrants investigation into insulin sensitivity and training volume balance.
Scenario 3: Low SHBG, high total testosterone You have a lot of free (active) testosterone. Monitor for over-training, inadequate recovery, or metabolic stress if SHBG drops suddenly.
Scenario 4: Low SHBG, low total testosterone Low free testosterone is expected, but low total suggests a deeper issue. See your GP for further investigation.
When to see a GP first: If you're experiencing fatigue, low mood, weak recovery, or sexual dysfunction alongside abnormal SHBG, total testosterone, or free testosterone results, consult your GP. They may investigate liver function, insulin sensitivity, thyroid health, or training load before jumping to supplementation.
What Affects Your SHBG
Training Volume and Type
High-volume endurance training (10+ hours per week) typically raises SHBG.[5] Moderate resistance training and periodised training lower it. Your training style is one of the strongest levers on SHBG.
Calorie Intake
Undereating raises SHBG as your body adapts to energy scarcity. Eating adequate calories for your training load helps normalise it.
Insulin Sensitivity
Better metabolic health (lower fasting glucose, better insulin response) correlates with lower SHBG.[4] This is why SHBG can be a marker of overall metabolic function, not just hormone status.
Alcohol Consumption
Excess alcohol (more than 2–3 drinks per day) increases SHBG. Moderate or no alcohol supports healthier levels.
Age and Body Composition
SHBG naturally increases slightly with age. Higher body fat tends to lower SHBG slightly.
Liver Function
SHBG is produced in the liver. Liver stress or disease can affect production. This is another reason your GP may want to check liver markers if SHBG is very high or low.
When to Retest
SHBG is relatively stable: it doesn't fluctuate like cortisol or testosterone. Annual testing is sufficient for most people, usually as part of a broader hormone panel. Retest if:
- You've significantly changed training type (switched from running to strength training, or vice versa)
- Your total testosterone or free testosterone has shifted
- Metabolic markers (glucose, insulin) have changed
- Your GP recommends it based on symptoms or other findings
FAQ
What's the difference between free testosterone and SHBG? SHBG is the carrier protein; free testosterone is the hormone not attached to any carrier. SHBG controls how much testosterone is free. High SHBG means more testosterone is carried (bound) and less is free.
Can I lower my SHBG naturally? Yes. Adequate calorie intake, resistance training, and good insulin sensitivity all support lower (more optimal) SHBG. Reducing high-volume endurance training can also help. These changes take weeks to months.
Does SHBG tell me if I have a hormone problem? SHBG is one piece of the puzzle. It's best interpreted with total testosterone, free testosterone, oestrogen, and FSH/LH. Don't diagnose yourself on SHBG alone; work with your GP or a sports medicine specialist.
Why do athletes with high SHBG still perform well? Adaptation. High SHBG is normal for endurance athletes; their tissues adapt to lower free hormone. The risk is when you switch to strength training or racing without adjusting for it: you might hit a performance plateau.
Should I supplement if my SHBG is high? Not without medical guidance. High SHBG usually reflects training adaptations or metabolic factors, not a deficiency requiring supplementation. Your GP should investigate the cause first. Supplementing testosterone without addressing the root cause often backfires.
