Sex Hormone Binding Globulin (SHBG) is a protein produced primarily by the liver that plays a role in regulating hormone activity. It binds to sex hormones like testosterone and estrogen, influencing their availability to tissues. Elevated SHBG levels can alter the balance of circulating hormones, leading to health implications. Understanding SHBG’s function and the factors that cause its levels to rise is important for maintaining hormonal health.
The Role of Sex Hormone Binding Globulin
SHBG is a glycoprotein circulating in the bloodstream, binding and transporting sex hormones like testosterone, dihydrotestosterone (DHT), and estradiol. Only a small fraction of these hormones remains unbound, or “free,” and thus biologically active. The majority of circulating testosterone and estradiol are either loosely bound to albumin or tightly bound to SHBG.
Bound to SHBG, sex hormones are inactive and cannot readily enter cells. SHBG thus acts as a regulator, controlling the amount of biologically active hormones available to tissues. The relative binding affinity of SHBG is highest for dihydrotestosterone, followed by testosterone, and then estradiol. This regulatory function maintains hormonal balance.
Common Causes of Elevated SHBG
Several factors and medical conditions can elevate SHBG levels. Hyperthyroidism, where the thyroid gland produces excessive hormones, is a frequent cause, as high thyroid levels stimulate liver SHBG production. Liver conditions, such as hepatitis and cirrhosis, can also contribute to elevated SHBG, though in advanced stages of cirrhosis, SHBG levels might decline.
Certain medications also raise SHBG levels. Oral contraceptives, containing synthetic estrogen, are a common example, significantly increasing liver SHBG production. Some anticonvulsant drugs and antipsychotics also elevate SHBG. Pregnancy naturally leads to a substantial increase in SHBG levels, often five to tenfold.
Lifestyle factors also influence SHBG concentrations. Significant caloric restriction, very low-fat diets, and excessive exercise can elevate SHBG, as the body interprets these as stress signals. Low body weight and insufficient protein intake may also be associated with higher SHBG. SHBG levels also tend to increase naturally with age, particularly in men.
Impact of High SHBG on Hormone Balance
Elevated SHBG levels significantly impact hormone balance by reducing “free” or biologically active sex hormones available to tissues. When more hormones are bound to SHBG, fewer interact with target cells, potentially causing hormone deficiency symptoms even if total hormone levels appear normal. This is particularly relevant for free testosterone and estrogen.
In men, high SHBG can cause symptoms of low free testosterone. These may include fatigue, reduced libido, and difficulty maintaining muscle mass. It can also contribute to osteoporosis risk and metabolic syndrome. The reduction in free testosterone can influence overall energy levels and mood.
For women, elevated SHBG can similarly lead to symptoms of reduced free estrogen and testosterone. Potential manifestations include low libido, vaginal dryness, and irregular menstrual cycles. High SHBG may also contribute to bone density concerns and impact fertility. The severity of these symptoms often correlates with how high the SHBG levels are.
Diagnosis and Management of Elevated SHBG
Diagnosing elevated SHBG typically involves blood tests. A healthcare provider will measure total SHBG levels, often alongside total testosterone and calculated free testosterone, to assess the balance of hormones. This comprehensive testing helps determine sex hormone availability, providing a clearer picture of hormonal health. Symptoms are evaluated in conjunction with laboratory results to guide diagnosis.
Management of elevated SHBG primarily focuses on addressing the underlying cause, rather than directly targeting SHBG. If hyperthyroidism is present, normalizing thyroid function through treatment can help reduce SHBG levels. For medication-induced elevations, such as those caused by oral contraceptives, healthcare providers may consider adjusting medications or exploring alternative options.
Lifestyle modifications can also play a supportive role. Maintaining a healthy body weight and ensuring adequate caloric and protein intake can be beneficial, as severe caloric restriction or low protein intake can elevate SHBG. Regular physical activity may also help normalize SHBG levels, particularly in individuals with metabolic imbalances. Consulting a healthcare professional is important for personalized advice and a tailored management plan.