Sex hormone-binding globulin (SHBG) is a protein primarily produced by the liver that circulates in the bloodstream. Its main function involves transporting sex hormones, such as testosterone and estrogen, throughout the body. When SHBG levels are elevated, it can lead to a reduction in the amount of free, active sex hormones available, potentially causing symptoms associated with lower levels of these hormones. This can impact various bodily functions and overall well-being.
The Role of SHBG and Its Impact When High
SHBG acts as a transporter for sex hormones, including testosterone, dihydrotestosterone (DHT), and estradiol, a type of estrogen. It binds to these hormones, making them inactive and unavailable for use by the body’s tissues. Only hormones that are “free” or unbound to proteins like SHBG can interact with cells and exert their effects.
When SHBG levels are high, a greater proportion of these sex hormones become bound and inactive. This means that even if the total amount of a hormone like testosterone in the blood is within a normal range, the amount of “free” or biologically active testosterone can be significantly reduced. This reduction in free hormones affects various systems dependent on adequate sex hormone signaling. This imbalance can disrupt processes related to sexual development, reproductive health, and overall well-being.
Common Causes of Elevated SHBG
Several conditions and factors can lead to an increase in SHBG levels. Hyperthyroidism, a condition where the thyroid gland produces too much thyroid hormone, is a known cause of elevated SHBG. The excess thyroid hormones can stimulate the liver to produce more SHBG.
Anorexia nervosa, an eating disorder characterized by severe calorie restriction and low body weight, can also result in high SHBG levels. This is due to the body’s altered metabolic state and hormonal regulation. Pregnancy naturally causes a significant increase in SHBG due to high estrogen levels activating SHBG production in the liver. This rise in SHBG during pregnancy helps protect the mother from exposure to fetal androgens.
Low testosterone levels can lead to increased SHBG as the body attempts to compensate for the perceived lack of available hormone. Low growth hormone levels also contribute to elevated SHBG. Liver diseases, such as hepatitis, can also impact SHBG production.
Lifestyle factors also play a role in SHBG regulation. Chronic alcohol consumption can affect liver function and hormone metabolism, contributing to elevated SHBG levels. Smoking has also been associated with higher SHBG.
Recognizing the Signs
High SHBG levels, by reducing the amount of free sex hormones, can manifest through a variety of symptoms that are essentially those of low free testosterone or estrogen. In men, common signs can include infertility and a decrease in libido. Men might also experience reduced testicle size and the development of breast tissue, a condition known as gynecomastia.
For women, elevated SHBG can lead to irregular menstrual periods or even absent periods. They may also experience a decreased libido and vaginal dryness. These symptoms stem from the limited availability of active estrogens and androgens needed for normal female reproductive and sexual function. High SHBG levels have also been linked to broader health concerns over the long term, including bone loss and an association with Alzheimer’s disease, reflecting the pervasive influence of sex hormones on various body systems.
Diagnosis and Management Approaches
Diagnosing high SHBG involves blood tests that measure total testosterone, free testosterone, and SHBG levels. A healthcare professional will interpret these results alongside a patient’s symptoms and medical history to determine if elevated SHBG is contributing to their health concerns. The total testosterone test provides a measurement of all testosterone in the blood, while the SHBG test helps determine how much of that testosterone is free and active.
Management of high SHBG primarily focuses on addressing the underlying cause. For instance, if hyperthyroidism is identified, treating the overactive thyroid gland helps normalize SHBG levels. Similarly, nutritional support and treatment for anorexia nervosa can restore hormonal balance. For lifestyle factors like alcohol consumption or smoking, reducing or eliminating these habits can contribute to healthier SHBG levels. Direct SHBG-lowering medications are not a common treatment; instead, the strategy involves mitigating the root cause to restore appropriate sex hormone availability.