Guide to Sex Hormone Binding Globulin (SHBG)

WRITTEN BY

The Levels Team

Updated: 05/22/2025|12 min read

Summary

Sex hormone binding globulin (SHBG) is a protein that regulates the availability of sex hormones in your body, particularly testosterone and estrogen. Your SHBG levels can help reveal underlying hormonal imbalances that might affect energy levels, reproductive health, and metabolism in both men and women.

Why It Matters

SHBG acts as a transport protein in the blood, binding to testosterone and estrogen to regulate how much of these hormones are available for your body. When SHBG binds to these hormones, they become inactive and can't enter cells. Only these hormones' unbound or "free" portion is biologically active.

In men, SHBG primarily affects testosterone availability, which controls sex drive, maintains muscle mass, and helps make sperm (it also affects estrogen in men). As men age, SHBG naturally increases, causing a decline in free testosterone even when total testosterone levels appear normal. This can affect muscle mass, bone density, sexual function, energy levels, and cognitive health.

In women, SHBG helps regulate both testosterone and estrogen levels, affecting menstrual cycles, fertility, and various aspects of reproductive health. Women naturally have higher SHBG levels than men due to estrogen's effect of increasing SHBG production. However, conditions like polycystic ovary syndrome (PCOS) can cause abnormally low SHBG levels, leading to excess free testosterone and associated symptoms.

Abnormal SHBG levels can signal underlying health issues in both men and women. Low SHBG may indicate insulin resistance, metabolic syndrome, excess androgen production, or increased cardiovascular risk. High SHBG levels may point to liver disease, hyperthyroidism, or hormonal imbalances, but also rises in any kind of hormone therapy and excessive exercise.

Associated Symptoms 

SHBG levels themselves are laboratory findings rather than medical conditions. However, abnormal levels may be associated with various health issues, each with its own symptoms.

Common symptoms that may indicate conditions associated with low SHBG:

• Metabolic changes: Increased abdominal fat and insulin resistance, potentially resulting from the underlying metabolic dysfunction that suppresses SHBG
• Skin issues: Acne, oily skin, and seborrhea may be due to increased free testosterone activity on sebaceous glands
• Mood alterations: Irritability or mood swings can be related to hormonal fluctuations
• Hypothyroidism: May cause fatigue, weight gain, depression, and cold intolerance due to slowed metabolism, which can contribute to lower SHBG levels

In women, low SHBG may additionally cause:

• Menstrual irregularities: Infrequent or absent periods may be due to hormonal imbalance affecting ovulation
• Hirsutism: Excessive facial and body hair growth can result from increased free testosterone
• Scalp hair thinning: Male-pattern hair loss potentially resulting from increased androgen activity on hair follicles
• Fertility challenges: Difficulty conceiving can be related to disrupted ovulation and hormonal imbalance

Common symptoms that may indicate conditions associated with high SHBG:

• Fatigue: Persistent tiredness potentially resulting from altered hormonal signaling and metabolism
• Decreased muscle mass: Reduced strength and tone may be due to decreased free testosterone availability
• Bone density concerns: Gradual bone mineral loss can result from reduced sex hormone activity on bone tissue

In men, high SHBG may additionally cause:

• Sexual dysfunction: Reduced libido and erectile difficulties can result from decreased free testosterone availability
• Reduced body hair: Thinning of facial and body hair may be due to decreased androgen effect

It's important to understand that SHBG's primary role is regulating the bioavailability of sex hormones. Therefore, symptoms of abnormal SHBG may reflect the resulting imbalance in free hormone levels rather than direct effects of SHBG itself. Many factors can influence both SHBG levels and symptoms, including age, weight, medications, and underlying health conditions.

Clinical Ranges

Female

• 18-55 Years: 17-124 nmol/L

• 55 Years: 14-73 nmol/L

Male

• 18-55 Years: 10-50 nmol/L

• 55 Years: 22-77 nmol/L

Lifestyle Factors That Can Impact It

• Diet: High-protein diets can lower SHBG levels, while fiber-rich diets may increase them. Plant-based diets typically lead to higher SHBG levels compared to diets high in animal products and saturated fats, which tend to suppress SHBG.
• Exercise: Regular moderate to vigorous physical activity increases SHBG production, helping to maintain hormonal balance. Resistance training can temporarily lower SHBG, increasing free testosterone, while extreme endurance exercise may raise SHBG levels.
• Weight management: Obesity, particularly abdominal fat, is strongly associated with decreased SHBG levels. Even 5-10% weight loss can significantly increase SHBG in people with obesity, improving overall hormonal balance.
• Alcohol: Moderate to heavy alcohol use can damage the liver and alter SHBG production.
• Sleep quality: Poor sleep patterns and disorders can disrupt hormonal balance, including SHBG production. Obstructive sleep apnea is associated with lower SHBG levels.

Other Factors That Can Impact It

Genetic Conditions

• Several genetic variants affect baseline SHBG levels in men and make some men more susceptible to conditions like metabolic syndrome or androgen imbalances.
• Mutations in the SHBG gene can lead to abnormally low SHBG levels, affecting hormone metabolism.

Medical Conditions

• Thyroid disorders: Hyperthyroidism can increase SHBG levels as thyroid hormones stimulate SHBG production. Conversely, hypothyroidism can decrease SHBG, though people with hypothyroidism may have normal levels.
• Liver disease: Cirrhosis, hepatitis, and other liver diseases often increase SHBG levels because it's produced in the liver.
• Insulin resistance and diabetes: These conditions suppress SHBG production, as insulin directly inhibits the liver's SHBG synthesis.
• Hypogonadism: Primary or secondary hypogonadism can affect SHBG levels through changes in sex hormone production and metabolism.
• Cushing's syndrome: Excess cortisol production suppresses SHBG synthesis.

Medications and Supplements

• Anti-epileptic medications
• Glucocorticoids
• Growth hormone therapy
• Testosterone therapy
• Metformin
• Statins
• Anabolic steroids
• Thyroid medications
• Anti-androgens

Individual Factors

• Age: SHBG levels naturally increase with age in men. This contributes to declining free testosterone levels in older males, potentially affecting muscle mass, libido, and energy levels, even when total testosterone appears within normal range.
• Body composition: Increased body fat, especially abdominal fat, is associated with lower SHBG levels. 

Testing Accuracy and Stability

SHBG tests are generally reliable, but your doctor will interpret results in the context of other hormonal and metabolic markers. Several factors can affect test results.

Factors That Can Affect the Accuracy of Your Test 

• Recent hormone fluctuations (within 2-3 days before testing) can temporarily alter SHBG production
• Acute illness or infection can increase SHBG levels due to inflammation
• Significant weight change in the weeks preceding the test can increase or decrease levels
• Recent intense exercise can temporarily elevate SHBG levels for 24-48 hours
• Dehydration can artificially concentrate blood components, including SHBG, leading to falsely elevated readings

How It Relates to Other Markers

Other tests can provide insights about health status when viewed alongside SHBG results. These tests may include:

• Total and free testosterone: SHBG directly affects the amount of biologically active testosterone.
• Estradiol (E2): Elevated estradiol can increase SHBG.
• Thyroid function tests (TSH, free T3, free T4): Thyroid disorders can impact SHBG levels.
• Fasting glucose and insulin: These markers help assess insulin resistance, which suppresses SHBG production.
• Liver function tests: As SHBG is produced in the liver, abnormal levels may indicate liver dysfunction.

What Results May Mean in the Context of Other Markers

• Low SHBG + normal/high total testosterone + high free testosterone: May suggest excessive androgen activity despite potentially normal total testosterone readings.
• High SHBG + normal total testosterone + low free testosterone: Common in aging men, this pattern can explain why some men experience symptoms of testosterone deficiency despite normal total testosterone readings.
• Low SHBG + low total testosterone: May still result in adequate free testosterone levels, potentially explaining why some men with apparently low total testosterone may not experience symptoms.
• Low SHBG + elevated liver enzymes + abnormal lipids: May suggest non-alcoholic fatty liver disease (NAFLD), now also called metabolic dysfunction-associated steatotic liver disease (MASLD). 
• High SHBG + low TSH + elevated T4/T3: May suggest hyperthyroidism, where excessive thyroid hormone stimulates SHBG production.

Follow-up Considerations

If SHBG is abnormal, your provider may make some of the following recommendations. You should always speak to your doctor if you have medical questions or before making medical decisions.

When Re-Testing May be Appropriate

• 3-6 months after starting testosterone replacement therapy or other hormonal treatments
• After significant weight loss (>10% of body weight)
• When changing medications that affect SHBG or testosterone levels
• If symptoms worsen despite treatment 
• Annually, for monitoring known conditions that affect hormone balance

Additional Testing Your Doctor May Consider

• Comprehensive metabolic panel to assess overall metabolic health
• Lipid profile to evaluate cardiovascular risk
• If taking testosterone, testing for hemoglobin and hematocrit to monitor for polycythemia, which causes an excess of red blood cells. Testosterone treatment increases the risk.
• Bone density scan if chronically abnormal sex hormone levels are present
• Advanced insulin resistance testing (HOMA-IR, glucose tolerance test)
• Comprehensive thyroid antibody testing if thyroid dysfunction is suspected
• Prostate-specific antigen (PSA) testing in men over 40, if testosterone therapy is being considered

When Additional Care May be Warranted

• Severe symptoms of hormone imbalance despite normal test results
• If SHBG levels are extremely high or low
• If liver function tests are abnormal
• When sexual dysfunction persists 
• If metabolic parameters worsen despite lifestyle interventions
• When considering fertility and SHBG or testosterone levels are abnormal

Bibliography