If you’ve had hormone testing and were told your SHBG is elevated, it’s natural to wonder what that means and whether it’s a problem. The answer is more nuanced than many people realize. In some cases, high SHBG reflects excellent metabolic health. In others, it may signal an imbalance that deserves attention. For active women, particularly those in training for a long running race, triathalon, or just being overly active in the gym, a very high SHBG can provide important clues about hormone status, energy availability, recovery, and long-term health.
What Is SHBG?
Sex Hormone-Binding Globulin (SHBG) is a protein produced primarily by the liver. Its job is to bind sex hormones, particularly:
- Testosterone
- Estradiol (estrogen)
- Dihydrotestosterone (DHT)
When hormones are bound to SHBG, they are largely unavailable for use by tissues. Only the “free” or unbound portion can readily interact with receptors and exert biological effects.
Think of SHBG as a transportation and storage protein. The higher the SHBG, the more hormone becomes tied up, leaving less available to tissues.
Why Does High SHBG Matter?
A woman can have hormone levels that appear “normal” on standard testing but still experience symptoms because excessive SHBG is binding a large percentage of those hormones.
Elevated SHBG may lead to lower levels of:
- Free testosterone
- Free estradiol
- Complex relationships with thyroid, DHEA, and cortisol exist
This can contribute to symptoms such as:
- Fatigue
- Reduced exercise recovery
- Decreased libido
- Difficulty building or maintaining muscle mass
- Bone loss over time
- Menstrual irregularities
The effect is especially important in women who train intensely or have low body fat.
The Most Common Cause in Endurance Athletes: RED-S
For a healthy 40-year-old woman training for a marathon and taking no medications, the most likely explanation for very high SHBG is Relative Energy Deficiency in Sport (RED-S).
RED-S occurs when caloric intake is insufficient relative to exercise demands. The athlete may feel healthy and perform well, but physiologically the body is operating in an energy-conserving state.
Emotional strain can worsen this condition.
How RED-S Raises SHBG
Several mechanisms contribute:
1. Low Energy Availability
When energy intake falls below the body’s needs, insulin levels tend to decrease. Insulin normally suppresses SHBG production in the liver. As insulin falls, SHBG production increases.
Research has shown that low energy availability in athletes is associated with hormonal changes including increased SHBG and reductions in anabolic hormones.
2. Low Body Fat and Low Insulin
SHBG is inversely related to:
- Body mass index (BMI)
- Visceral fat
- Fasting insulin levels
Lean endurance athletes commonly have low insulin concentrations and low body fat stores. Both favor increased SHBG production by the liver. Alcohol consumption usually lowers SHBG, but in small studies premenopausal you see elveation.
3. A Higher Estrogen-to-Androgen Ratio
Estradiol stimulates SHBG production, while androgens tend to suppress it.
In many female endurance athletes, testosterone levels decrease while estrogen production remains relatively preserved. This creates a hormonal environment that further pushes SHBG higher.
High SHBG Is Not Always a Good Thing
Many people associate high SHBG with excellent metabolic health because it is often seen in lean individuals with low insulin levels.
However, very high SHBG can become problematic when it reduces free hormone levels excessively.
In women, this may contribute to:
- Poor training recovery
- Persistent fatigue
- Decreased libido
- Reduced muscle adaptation
- Declining bone density
- Menstrual dysfunction
When these features are present, the issue is not SHBG itself but what the elevated SHBG may be revealing about overall physiology.
Other Important Causes of Elevated SHBG
While RED-S is often the most likely explanation in endurance athletes, several medical conditions should be excluded.
Hyperthyroidism
Thyroid hormones directly stimulate SHBG production by the liver.
Even mild or subclinical hyperthyroidism can raise SHBG significantly. Because of this, a thyroid evaluation should be part of the workup for unexplained SHBG elevation.
Liver Disease
Since SHBG is produced in the liver, chronic liver disease can alter SHBG production.
Although uncommon in otherwise healthy, active women, obtaining liver function tests is reasonable when SHBG is markedly elevated.
Restrictive Eating Patterns or Eating Disorders
Eating disorders are a recognized cause of elevated SHBG.
Sometimes marathon training can obscure underlying caloric restriction because weight loss and leanness may be viewed as expected consequences of training. The overlap between eating disorders and RED-S is substantial.
Recommended Evaluation
For women with significantly elevated SHBG, a comprehensive evaluation may include:
Thyroid Testing
- TSH
- Free T4
Sex Hormone Assessment
- Estradiol
- Total testosterone
- Free testosterone
- DHEA-S
Metabolic Markers
- Fasting insulin
- Fasting glucose
Liver Function Tests
- AST
- ALT
- Albumin
Clinical History
- Menstrual regularity
- Exercise volume
- Daily calorie intake
- History of stress fractures
- Recovery capacity
- Libido and energy levels
- Hair health
Why Menstrual History Matters
Menstrual changes are often one of the earliest warning signs that energy availability is inadequate.
Questions worth asking include:
- Have cycles become irregular?
- Are periods lighter than they used to be?
- Have periods stopped altogether?
- Is recovery from training worsening?
Women experiencing menstrual irregularities, recurrent injuries, or stress fractures may be showing signs of RED-S and should be evaluated more thoroughly.
The Bottom Line
In a 40-year-old woman training for a marathon, very high SHBG most commonly reflects low energy availability and Relative Energy Deficiency in Sport (RED-S) rather than a primary hormone disorder.
While elevated SHBG is often associated with a lean and metabolically healthy profile, excessively high levels can significantly lower free testosterone and free estradiol, affecting recovery, bone health, performance, and reproductive function.
A thorough evaluation should include thyroid testing, liver function assessment, reproductive hormones, fasting insulin, and a careful review of training volume, nutrition, and menstrual health. Identifying the root cause is critical because, in many cases, SHBG is acting as an early warning signal that the body is not receiving enough energy to support both athletic performance and optimal hormonal health.
