When most men have hormone testing done, they immediately look at their testosterone level. If it's within the laboratory reference range, they assume everything is fine. However, one of the most misunderstood, and often ignored, markers on a hormone panel is sex hormone-binding globulin (SHBG). I frequently see men with symptoms of low testosterone despite a "normal" total testosterone, only to discover that an abnormal SHBG level is changing how much testosterone is actually available to their body. Likewise, men undergoing infertility evaluations often ask whether SHBG affects sperm production. The answer is yes, but not always in the way people think.

SHBG is a protein produced primarily by the liver. Its job is to bind sex hormones, particularly testosterone and estradiol, and transport them through the bloodstream. Think of SHBG as a taxi service for hormones. Once testosterone is attached to SHBG, it is largely unavailable to tissues until it dissociates from the protein. Approximately 40–60% of circulating testosterone is tightly bound to SHBG, another 40–50% is loosely bound to albumin, and only 1–3% circulates as free testosterone, which is the biologically active form capable of entering cells and activating androgen receptors.

This is why measuring total testosterone alone can sometimes be misleading. Two men may both have a total testosterone of 500 ng/dL, yet one has very high SHBG and very little free testosterone, while the other has low SHBG and an abundance of free testosterone. Clinically, these men can feel completely different despite identical total testosterone levels.

One of the most common questions I receive is whether SHBG itself causes symptoms. The answer is not directly. SHBG is not a hormone; it is a carrier protein. The symptoms occur because abnormal SHBG changes the amount of bioavailable testosterone reaching tissues such as muscle, bone, brain, and the reproductive tract.

High SHBG typically results in less free testosterone. Men may experience fatigue, reduced libido, erectile dysfunction, decreased muscle mass, reduced exercise recovery, lower energy, and sometimes infertility despite having a normal total testosterone level. Conversely, low SHBG often increases free testosterone, although this does not necessarily mean a man has "high testosterone." In fact, many obese men have low SHBG and relatively low total testosterone, yet maintain near-normal free testosterone.

So what causes SHBG to become elevated? One of the strongest predictors is aging. SHBG naturally increases as men get older, which partly explains why free testosterone declines more rapidly than total testosterone. Hyperthyroidism is another well-recognized cause because thyroid hormone stimulates hepatic SHBG production. Liver disease, HIV infection, certain anticonvulsant medications, and excessive estrogen exposure can also increase SHBG. Interestingly, men who are extremely lean or endurance athletes sometimes develop higher SHBG levels as well. Genetics also play an important role, and some men simply inherit naturally higher SHBG concentrations without any underlying disease.

On the other hand, low SHBG is commonly associated with obesity, insulin resistance, metabolic syndrome, type 2 diabetes, hypothyroidism, non-alcoholic fatty liver disease, and chronic inflammation. Elevated insulin suppresses SHBG production by the liver, which is why overweight men frequently have lower SHBG levels. Anabolic steroid use, glucocorticoids, and elevated growth hormone can also suppress SHBG.

This relationship between SHBG and metabolism has become increasingly important in men's health. Numerous studies have shown that low SHBG is independently associated with insulin resistance and future development of type 2 diabetes, even before diabetes develops. In other words, SHBG may serve as an early marker of metabolic health, not simply reproductive health.

How does SHBG affect fertility? This is where many misconceptions arise. SHBG itself does not directly control sperm production. Spermatogenesis depends primarily on FSH, LH, intratesticular testosterone, and healthy Sertoli and Leydig cell function. However, SHBG influences the amount of testosterone available throughout the body, which can indirectly affect the hormonal environment supporting sperm production.

For example, a man with very high SHBG may have a normal total testosterone but insufficient free testosterone. If symptoms suggest androgen deficiency, further evaluation is warranted because free testosterone, not just total testosterone, helps determine whether the body is receiving adequate androgen stimulation. Conversely, low SHBG often accompanies obesity and metabolic dysfunction, conditions themselves associated with impaired semen quality, increased oxidative stress, reduced sperm concentration, and increased DNA fragmentation.

Several studies have demonstrated associations between abnormal SHBG and semen quality, although these relationships are often indirect. Men with obesity, diabetes, or metabolic syndrome frequently have both low SHBG and impaired sperm production. Similarly, men with hyperthyroidism may have elevated SHBG and altered reproductive hormone balance. In most cases, SHBG is acting as a marker of the underlying condition rather than being the primary cause of infertility.

Should SHBG be measured in every infertility patient? I believe it has value, particularly when testosterone levels don't match a patient's symptoms. Current guidelines recommend measuring morning total testosterone initially. If total testosterone is borderline or symptoms are disproportionate to the laboratory value, measuring SHBG allows calculation of free testosterone, providing a much more accurate picture of androgen status. This is especially useful in men who are obese, very lean, older, or have thyroid disease or diabetes.

One of the biggest mistakes I see is men focusing exclusively on increasing testosterone without understanding SHBG. There are no medications specifically approved to lower or raise SHBG for fertility purposes. Instead, treatment should target the underlying condition. If SHBG is elevated because of hyperthyroidism, treating the thyroid disorder often normalizes SHBG. If SHBG is low because of obesity and insulin resistance, weight loss, improved diet, exercise, and treatment of metabolic disease frequently increase SHBG toward normal while improving overall health.

For men with fertility concerns, lifestyle modifications remain some of the most effective interventions. Achieving a healthy body weight, exercising regularly, improving sleep quality, limiting alcohol, avoiding tobacco and anabolic steroids, optimizing thyroid function, and managing diabetes all support both hormonal health and sperm production. These interventions often improve testosterone balance without directly targeting SHBG itself.

It's also important to remember that taking testosterone replacement therapy (TRT) is not the solution for most men trying to conceive. While TRT often improves symptoms of low testosterone, it suppresses LH and FSH production, dramatically reducing intratesticular testosterone and often shutting down sperm production. Men who desire fertility should instead discuss fertility-preserving options such as clomiphene citrate, enclomiphene, or hCG, depending on their hormonal profile.

Ultimately, SHBG is best viewed as one piece of a much larger puzzle. An abnormal SHBG level does not automatically mean you have low testosterone or infertility. Likewise, a normal SHBG does not guarantee normal reproductive function. It must always be interpreted alongside total testosterone, calculated or measured free testosterone, LH, FSH, estradiol, prolactin, thyroid function, semen analysis, and the patient's symptoms.

The most important takeaway is this: don't ignore SHBG, but don't obsess over it either. It is an important laboratory marker that helps explain why some men feel poorly despite "normal" testosterone levels and why others have surprisingly normal function despite low total testosterone. For fertility specialists, SHBG provides valuable insight into the hormonal environment supporting spermatogenesis, but it is rarely the sole explanation for infertility. Treat the patient, not just the laboratory value, and always search for the underlying cause of an abnormal SHBG before considering hormone therapy.

References

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