Low SHBG and low testosterone often appear together, and the cause is usually the same underlying condition driving both. SHBG, or sex hormone-binding globulin, is a protein made by the liver that carries testosterone and estrogen through the blood. When SHBG levels drop, the body clears testosterone faster, which pulls total testosterone down with it. The most common triggers are insulin resistance, obesity, type 2 diabetes, liver disease, and certain medications like steroids or seizure drugs.
What Is SHBG and Why Does It Matter?
SHBG acts like a transport vehicle for sex hormones. Most testosterone in your blood is attached to SHBG or to another protein called albumin. Only a small fraction, about 2 percent, floats free and is biologically active.
When SHBG is low, less testosterone stays bound in the blood. That sounds like it should raise free testosterone, but it often does the opposite. The liver clears unbound testosterone quickly, so total testosterone levels fall. Some men end up with low total testosterone and normal or even high free testosterone. Others end up with both total and free testosterone below normal.
This distinction matters because standard blood tests usually measure total testosterone. If your SHBG is low, your total testosterone number may look alarming even when your free testosterone is fine. A doctor who only checks total testosterone might miss the full picture.
Insulin Resistance and Obesity Are the Biggest Drivers
Insulin resistance is the most common cause of low SHBG. When your cells stop responding normally to insulin, your pancreas makes more insulin to compensate. High insulin levels tell the liver to produce less SHBG.
This creates a chain reaction. Insulin resistance leads to more insulin. More insulin leads to lower SHBG. Lower SHBG leads to faster testosterone clearance. The result is low total testosterone.
Obesity, especially excess belly fat, strongly promotes insulin resistance. Fat tissue also converts testosterone into estrogen through an enzyme called aromatase. This further lowers testosterone while raising estrogen. Weight gain and low testosterone feed each other in a cycle that can be hard to break.
Research consistently shows that weight loss improves both SHBG and testosterone levels. Even modest weight loss of 5 to 10 percent of body weight can raise SHBG meaningfully. This is one of the few interventions with solid evidence behind it.
Type 2 Diabetes and Metabolic Syndrome
Type 2 diabetes is closely tied to low SHBG. In fact, low SHBG is considered a risk marker for developing type 2 diabetes, not just a consequence of it. Some studies suggest that men with low SHBG are more likely to develop diabetes years later.
Metabolic syndrome, a cluster of conditions including high blood pressure, high blood sugar, excess belly fat, and abnormal cholesterol, also tracks with low SHBG. The shared thread is insulin resistance.
If you have diabetes or metabolic syndrome, your low testosterone may be a downstream effect of your metabolic health rather than a primary hormone problem. Treating the metabolic condition often improves testosterone without any hormone therapy.
Liver Disease and SHBG Production
The liver makes SHBG, so liver health directly affects SHBG levels. Chronic liver conditions like fatty liver disease, hepatitis, and cirrhosis can lower SHBG production.
Non-alcoholic fatty liver disease is increasingly common and often goes unnoticed. It is strongly associated with obesity and insulin resistance. Many men with low SHBG and low testosterone also have fatty liver, even if they have never been diagnosed.
Liver disease can also affect testosterone through other pathways. The liver clears estrogen from the blood. When liver function declines, estrogen can build up, further suppressing testosterone production in the testes.
Medications That Lower SHBG
Several medications reduce SHBG levels. The most common are:
- Glucocorticoids like prednisone, used for inflammation and autoimmune conditions
- Progestins, found in some hormone therapies
- Androgens like anabolic steroids or testosterone itself
- Some seizure medications including phenytoin and carbamazepine
- Insulin and sulfonylureas, used for diabetes
If you take any of these and have low testosterone, the medication may be the cause. Never stop a prescribed medication on your own. Talk to your doctor about whether the drug could be affecting your hormone levels and whether alternatives exist.
Testosterone therapy itself lowers SHBG. This is why men on testosterone replacement often see their SHBG drop further. It is a normal response, not a sign the treatment is failing.
Other Causes: Thyroid, Aging, and Genetics
Thyroid hormone increases SHBG production. Low thyroid function, or hypothyroidism, can therefore lower SHBG. If you have untreated hypothyroidism, your SHBG and testosterone may both be low. Treating the thyroid condition can restore normal levels.
Aging also plays a role, though the effect is indirect. SHBG tends to rise with age in men, not fall. This means older men often have low total testosterone because more of it is bound to SHBG, leaving less free testosterone. This pattern is different from the low SHBG pattern seen in metabolic conditions.
Genetics matter too. Some men naturally produce less SHBG due to inherited variations in the SHBG gene. If you have always had low SHBG with normal metabolic health, genetics may be the explanation.
What Causes Low Shbg And Low Testosterone Together in the Same Person
When both SHBG and testosterone are low, the most likely explanation is insulin resistance or its related conditions. Obesity, type 2 diabetes, and metabolic syndrome all lower SHBG production and speed up testosterone clearance.
Liver disease is the second most common cause. Fatty liver, in particular, often coexists with insulin resistance. Both conditions lower SHBG through separate but overlapping pathways.
Medications are the third major cause. Glucocorticoids and certain seizure drugs lower SHBG directly. Androgen use, including testosterone therapy, also suppresses SHBG.
Less common causes include hypothyroidism, chronic inflammation, and genetic variations. Your doctor can distinguish between these by checking additional blood markers like fasting insulin, blood sugar, liver enzymes, and thyroid function.
How Doctors Diagnose the Underlying Cause
A single blood test is rarely enough. Doctors typically order a panel that includes total testosterone, SHBG, and sometimes free testosterone or albumin. From these, they can calculate free testosterone using a standard formula.
Additional tests depend on your symptoms and risk factors. Fasting glucose and insulin check for insulin resistance. Liver enzymes screen for liver disease. Thyroid-stimulating hormone checks thyroid function.
If you have low SHBG and low testosterone, the treatment depends entirely on the cause. Weight loss and better blood sugar control are the first-line approaches for metabolic causes. Treating an underlying liver or thyroid condition can restore normal hormone levels. Medication adjustments may help if a drug is the culprit.
Testosterone replacement therapy is not always the answer. If your free testosterone is normal, you may not need it despite a low total testosterone number. If your free testosterone is genuinely low, testosterone therapy can help, but it will not fix the underlying metabolic problem.
Frequently Asked Questions
Can low SHBG cause low testosterone?
Yes, low SHBG causes the liver to clear testosterone faster, which lowers total testosterone levels. Free testosterone may remain normal or also drop depending on the individual.
What is a normal SHBG level?
Normal ranges vary by lab, but most reference ranges for adult men fall between roughly 10 and 57 nmol/L. Your lab report will show the specific range used for your test.
Does weight loss increase SHBG?
Yes, weight loss raises SHBG levels, especially when it improves insulin sensitivity. Even a 5 to 10 percent reduction in body weight can meaningfully increase SHBG and total testosterone.
Is low SHBG dangerous?
Low SHBG itself is not dangerous, but it is a warning sign of metabolic problems like insulin resistance and fatty liver. It also increases the risk of developing type 2 diabetes.
