Sex Hormone-Binding Globulin (SHBG) is a protein produced primarily by the liver that manages the circulation of sex hormones in the bloodstream. It acts as a carrier for hormones like testosterone and estradiol, ensuring their transport throughout the body. When SHBG levels are low, the balance of these hormones is altered, leading to an increased amount of free, active hormones. Understanding SHBG function and the factors that suppress its production is important for comprehending the resulting physical and metabolic changes.
Understanding SHBG and Its Function
SHBG acts as a reservoir and regulator for sex hormones. Total hormone levels measured in the blood include the fraction bound to SHBG and the unbound fraction. Hormones bound to SHBG are considered biologically inactive because they cannot easily enter cells to exert their effects.
The small percentage of hormones not bound to SHBG or other proteins, such as albumin, is known as the “free” fraction. This free hormone is the biologically active portion that readily interacts with tissue receptors. When SHBG levels drop, fewer hormones are bound, increasing the proportion of free hormones. This increase in unbound, active hormones drives the symptoms associated with low SHBG.
Physical Manifestations of Low SHBG
The physical manifestations of low SHBG result from the increased biological activity of androgens, particularly free testosterone and dihydrotestosterone (DHT). Because SHBG has a strong affinity for these hormones, a decrease in the binding protein means a surge in their active forms. In women, this excess androgen activity often leads to hyperandrogenism, frequently seen in conditions like Polycystic Ovary Syndrome (PCOS).
Symptoms in women include hirsutism (the growth of coarse, dark hair in a male pattern), acne along the jawline, and male-pattern hair thinning or baldness. Reproductive symptoms include irregular or absent menstrual periods and difficulty conceiving.
Low SHBG is also linked to various metabolic changes. Individuals may experience abdominal obesity and difficulty maintaining muscle mass. Other signs include oily skin, enlarged pores, and darkened skin patches (acanthosis nigricans), which indicates insulin resistance. For men, excess free hormones can sometimes cause mood swings, fluid retention, or enlarged breast tissue due to the conversion of testosterone into estrogen.
Underlying Conditions That Decrease SHBG Production
The primary driver for decreased SHBG synthesis is often metabolic dysfunction. SHBG is produced by the liver, and its production is highly sensitive to the body’s metabolic environment. Insulin resistance and the resulting hyperinsulinemia are the most common factors that directly suppress SHBG production.
High levels of circulating insulin signal the liver to decrease its output of SHBG. Low SHBG often serves as an early marker for metabolic syndrome, a cluster of risk factors including high blood pressure, elevated blood sugar, and abnormal cholesterol levels. Obesity, especially excess visceral fat, is also consistently associated with reduced SHBG levels.
Type 2 diabetes is linked to low SHBG, as it is a progression of insulin resistance. High levels of circulating androgens, such as those in PCOS, also directly inhibit SHBG synthesis, creating a feedback loop. Other endocrine disorders, including hypothyroidism, Cushing’s disease, and nonalcoholic fatty liver disease, suppress the liver’s ability to produce this binding protein.
Strategies for Managing Low SHBG
Management involves addressing the underlying metabolic and endocrine conditions suppressing SHBG production. Since insulin resistance is a frequent cause, therapeutic efforts focus on improving insulin sensitivity. Dietary changes are foundational, emphasizing the reduction of refined carbohydrates and sugars to lower circulating insulin levels.
Regular physical activity is an impactful lifestyle intervention. Specific types of exercise, such as resistance training, can help improve insulin sensitivity and support a healthier body composition. Achieving and maintaining a healthy body weight is important, as weight loss has been shown to reverse the suppression and allow SHBG levels to rise.
In some cases, medical management is necessary. For individuals with hypothyroidism, treating the thyroid dysfunction can help normalize SHBG production. If insulin resistance or Type 2 diabetes is a factor, a healthcare provider may prescribe medications aimed at improving glucose control. The goal is to treat the metabolic environment where low SHBG developed, restoring overall hormonal health.