SHBGnmol/L
Testosterone/oestradiol binding capacity
Also known as: Sex Hormone Binding Globulin, Sex Hormone-Binding Globulin
Typical optimal range
18.3–54.1 nmol/L
Female
A commonly cited reference interval for SHBG is roughly 18.3–54.1 nmol/L, though exact ranges differ between laboratories, between men and women, and across age groups, so always interpret your result against your own lab's reference values. These figures are indicative — the range printed on your own lab report is the definitive one for your results.
Interpretation of SHBG follows NHS and laboratory-specific guidance; NICE guideline NG223 on testosterone deficiency and NHS guidance on conditions such as PCOS and hypothyroidism provide relevant clinical context for abnormal results.
What is SHBG?
SHBG (Sex Hormone-Binding Globulin) is a protein produced by the liver that binds tightly to sex hormones — chiefly testosterone and oestradiol — and carries them through the bloodstream. Only the hormone that is not bound to SHBG (often called 'free' or 'bioavailable' hormone) can act on body tissues. Because total testosterone or oestradiol tests measure both bound and free fractions together, measuring SHBG alongside them gives a much clearer picture of how much hormone is actually available to the body.
What a high SHBG means
A raised SHBG level suggests that more of your sex hormones are being 'locked away', potentially reducing the amount of biologically active testosterone or oestradiol available to tissues — even when a total hormone test looks normal. On its own this is not a diagnosis, but it is a useful prompt to look more closely at thyroid function, metabolic health, and overall hormone balance.
- Thyroid overactivity. The thyroid hormone thyroxine directly stimulates SHBG production in the liver. Hyperthyroidism — or even taking a higher-than-needed dose of levothyroxine — is one of the most common reasons SHBG rises, so thyroid function tests are often checked alongside it.
- Low insulin levels or very low carbohydrate intake. Insulin suppresses SHBG synthesis in the liver, so conditions or dietary patterns that keep insulin consistently low — including very low-carbohydrate diets and some restrictive eating patterns — can push SHBG upward. This is generally less concerning than a pathological cause, but worth noting.
- Advancing age. SHBG rises progressively with age, particularly in men, which partly explains why bioavailable testosterone falls even when total testosterone appears within range. In older adults this is an expected physiological change rather than a sign of disease.
A single elevated reading should always be interpreted in clinical context; factors such as recent illness, liver disease, and certain medications (including some anticonvulsants and oestrogen-containing contraceptives) can also raise SHBG. Repeat testing and a full hormone panel give a more reliable picture.
What a low SHBG means
A low SHBG level is often a meaningful metabolic signal, reflecting conditions that suppress its liver synthesis — most commonly insulin resistance and excess visceral fat. It is associated in population studies with an increased risk of type 2 diabetes and cardiovascular disease, so it is worth discussing with your GP, particularly if you have other metabolic risk factors.
- Insulin resistance and type 2 diabetes. Raised insulin levels directly suppress SHBG production in the liver. Low SHBG is now recognised as an early marker of insulin resistance, sometimes appearing before blood glucose becomes abnormal, making it a useful flag in metabolic health assessment.
- Obesity and excess visceral fat. Visceral (abdominal) fat drives higher circulating insulin and contributes to low-grade inflammation, both of which reduce SHBG. Weight loss — even modest amounts — typically raises SHBG back towards the reference range.
Low SHBG is also seen in hypothyroidism, polycystic ovary syndrome (PCOS), and with use of anabolic steroids or androgen therapy. Your GP will consider these possibilities alongside your full clinical picture.
Should I be worried?
A single out-of-range SHBG result is rarely cause for alarm on its own — it is most useful when interpreted alongside total testosterone, oestradiol, thyroid function, fasting glucose or HbA1c, and other metabolic markers. If your result is persistently outside the reference range or sits alongside symptoms (such as fatigue, changes in libido, menstrual irregularity, or weight gain), it is worth booking a GP appointment to discuss a broader hormone and metabolic check. Your GP can assess the full picture and, if needed, refer you to an endocrinologist or other specialist.
What actually helps
Because SHBG is closely tied to insulin sensitivity and liver metabolism, lifestyle changes that improve metabolic health tend to have the most meaningful impact on levels that are low.
- Improve insulin sensitivity. Regular physical activity — particularly a combination of aerobic exercise and resistance training — is one of the most effective ways to lower chronically raised insulin levels, which in turn allows SHBG to rise. Even brisk walking most days has been shown to improve insulin sensitivity.
- Reduce visceral fat. Losing excess abdominal fat, through a sustainable calorie deficit and increased activity, reliably raises SHBG in people whose levels are low due to overweight or obesity. A loss of 5–10% of body weight can produce meaningful improvements in metabolic markers including SHBG.
- Balance dietary macronutrients. Very high intakes of refined carbohydrates and added sugars promote insulin spikes that suppress SHBG. Shifting towards a diet richer in fibre, lean protein, and healthy fats supports more stable insulin levels and better SHBG balance.
- Support thyroid health. For those with confirmed thyroid conditions, ensuring that treatment is well-optimised (neither under- nor over-replaced) helps keep SHBG in a healthier range, since both hypothyroidism and hyperthyroidism push it in opposite directions.
There is good supporting evidence that certain foods and dietary patterns influence SHBG through their effects on insulin sensitivity and liver metabolism.
High-fibre vegetables and legumes
Dietary fibre slows glucose absorption, moderates post-meal insulin responses, and is independently associated with higher SHBG in epidemiological studies.
Oily fish (salmon, mackerel, sardines)
Omega-3 fatty acids support insulin sensitivity and have anti-inflammatory effects that may benefit liver metabolism and SHBG production.
Wholegrains (oats, rye, barley)
Replacing refined grains with wholegrains reduces glycaemic load and insulin demand, creating conditions more favourable to normal SHBG levels.
Nuts and seeds
Regular nut consumption is associated with improved insulin sensitivity and a healthier metabolic profile; flaxseed in particular has been studied in the context of sex hormone balance, though evidence remains preliminary.
Cruciferous vegetables (broccoli, cabbage, Brussels sprouts)
These vegetables support liver detoxification pathways involved in hormone metabolism and contribute to overall dietary fibre intake.
Track your own SHBG
Upload a lab PDF and Better Days trends SHBG over time, flags it when it drifts, and suggests foods that help.
More in Hormones
Sources & further reading
These are reputable UK health resources for further reading. This page is written to be consistent with their guidance but is not a substitute for them.
For information only — not medical advice, and not individually reviewed by a clinician. Reference ranges vary by lab and individual. Discuss any results with a qualified clinician before making changes.