Hormones are central to health. They can either act like the conductors of an orchestra, leading to a harmony of health and well-being, or they can create a cacophony of chaos.
Women's health experts primarily focus on estrogen, progesterone, and testosterone, but they aren't the only hormones at play. Sex hormone-binding globulin (SHBG) is a hormone that sits in the background but plays a vital role in maintaining the balance of some of these sex hormones. And while Western medicine may not always consider SHBG, I recommend it as part of a comprehensive hormone health assessment (especially if testosterone appears low).
Below, I'll share the details about SHBG, what it does, why it's so important, and what happens when it's too high or too low.
What is Sex Hormone-Binding Globulin (SHBG)
Sex Hormone-Binding Globulin (SHBG) is a protein made in your liver. It helps to bind and transport hormones like testosterone and estrogen throughout your body. SHBG has the highest affinity for testosterone, and it can bind to other hormones like dihydrotestosterone (DHT), estradiol (E2), and estrone (E1) too.
When hormones are bound to SHBG, they are inactive, so they can't travel freely and activate receptors in different parts of the body. This means that SHBG is essential in regulating hormone activity and influences the amount of free circulating hormones. Levels of SHBG naturally increase until puberty but then drops until about age 60, when it starts to rise again.
How Does SHBG Affect Testosterone Levels?
If SHBG levels are high, it means more testosterone is bound, and less is free or available for biological processes. This is why high SHBG can be associated with low testosterone levels, leading to symptoms like fatigue, decreased libido, body composition changes, and even cognitive issues.
On the other hand, having low SHBG levels can mean more free testosterone is available in the body. High testosterone can cause acne, hair loss, and facial hair growth.
I always check SHBG when evaluating testosterone levels in women for this reason. Tests may show high or low testosterone, but it may have less to do with actual levels of testosterone and more to do with SHBG levels causing an imbalance.
What Does it Mean When SHBG is High?
As mentioned, high SHBG means you have less available free testosterone (or sometimes estrogen). High SHBG symptoms look the same as low estrogen and testosterone:
- Decreased libido
- Irregular or missing periods
- Vaginal dryness
- Decreased muscle and bone mass
- Depression and mood disorders
Causes of High SHBG
Sometimes it's challenging to pinpoint the cause of high (or low) SHBG. There are some conditions associated with SHBG, but it's not clear if the condition is actually causing elevated levels or if higher SHBG is simply part of the underlying condition. Here are some possible causes of high SHBG:
- Pregnancy: Pregnancy increases SHBG levels, but interestingly it's lower in women with gestational diabetes likely because insulin resistance and SHBG levels have an inverse relationship.
- Underweight or Malnutrition: Some studies link high SHBG levels with anorexia, where levels went up when patients were given IV caloric infusions and when they gained weight.
- Hormonal Birth Control: The pill alters hormone production to halt ovulation. At the same time, it significantly increases SHBG—up to four times higher than women not taking the pill, according to one study.
In other words, the birth control pill not only lowers how much hormone your body makes, but the higher levels of SHBG mean even the hormones you have are less available—especially testosterone. This is one of the reasons the pill is often prescribed for PCOS, since it brings testosterone levels down so rapidly (but doesn't address the root causes).
- Hyperthyroid: Studies on people with hyperthyroid—a thyroid disease where the thyroid is making too much hormone—show higher levels of SHBG and, as a result, decreased free testosterone levels.
- Alcohol and smoking. Drinking may lead to higher SHBG levels. Smoking cigarettes may also lead to higher SHBG levels, but quitting smoking drops levels down quickly.
How to Lower SHBG
As with any hormonal imbalance, there's no single intervention or lifestyle habit that will automatically “fix” high SHBG levels, but here are some of the options I use in practice to lower SHBG:
- Zinc: A lot of the studies on SHBG, testosterone, and zinc are on men, but there is some research to suggest that zinc can help bring up testosterone, improve symptoms of low testosterone, and lower SHBG in women. You can find zinc in oysters, pumpkin seeds, and organ meat. Still, I often recommend supplementing to ensure my patients get enough.
- Stinging nettle: This herb has been used for centuries as a natural remedy to support healthy hormone levels. Research shows that stinging nettle can help lower SHBG and help make more testosterone available in the body.
- High-protein diet: Eating a high-protein diet may help reduce SHBG levels to free up sex hormones. In one study, men who ate more protein had lower SHBG levels. While we cannot assume that women would have the same result, we can take the message that protein is an essential piece of hormone balance and use it as a tool. Protein-rich foods include fish, poultry, eggs, legumes, seeds and nuts. Grab my free hormone balancing meal plan for more info on this!
What Does it Mean When SHBG is Low?
Low SHBG means more free testosterone and estrogen are available and circulating through the body. Low SHBG symptoms are those that present with high testosterone or estrogen, such as:
- Excessive facial and body hair (hirsutism)
- Irregular or missing periods
- Thinning hair
- Weight gain
- Mood swings
Causes of Low SHBG
Similar to high SHBG, some of these may or may not be causes, but may be associated with a health condition:
- Hypothyroid: Just as hyperthyroid can contribute to high SHBG, hypothyroid—when the body doesn't make enough thyroid hormone—can cause low SHBG levels. Studies are mixed as some research shows normal SHBG, even with low thyroid hormone levels, but others show decreased SHBG.
- PCOS: High androgens are a hallmark of PCOS. Some research suggests that low SHBG increases free testosterone in the body, but high androgens can also shut down SHBG production. Testing for low SHBG in PCOS should be part of a complete workup.
- Obesity and metabolic syndrome: There's a connection to excess body weight, metabolic syndrome (a grouping of symptoms like insulin resistance and elevated lipids), and low SHBG levels. Part of this may be related to insulin, the hormone that helps regulate blood sugar. Insulin can shut down the production of SHBG in the liver.
Insulin resistance, which means your cells aren't as sensitive as they should be to signals to lower blood sugar, is also closely related to PCOS. Research suggests that high insulin levels are linked to low SHBG in women with PCOS and type 2 diabetes.
How to Increase SHBG
- Myo-inositol: Inositol is one of my go-to supplement for PCOS because of its impact on metabolic and reproduction functions—including SHBG. One study found that a combination supplement of two forms of inositol (myo-inositol and d-chiro-inositol) significantly increased SHBG and decreased insulin and free testosterone.
Interestingly, a study comparing myo-inositol with berberine and Metformin, a medication often prescribed to women with PCOS, found that all three significantly increased SHBG, and myo-inositol showed the most benefit for carbohydrate metabolism.
- Intermittent fasting: We know intermittent fasting is beneficial in some cases, but it also should be used with caution for those with hormonal imbalance or adrenal dysfunction because of the stress it can put on the body.
However, intermittent fasting could benefit people with low SHBG. A recent review concluded that intermittent fasting may lower androgens like testosterone and could increase SHBG, especially if the eating window is earlier in the day. If you want to read and learn more about intermittent fasting and how it affects women, I've written extensively about it here.
- Vitamin D: Vitamin D is closely aligned with hormone balance and immune health. Studies link low vitamin D levels to higher free testosterone and lower SHBG. Ideally, get your vitamin D levels checked to see if you need supplementation, but I usually suggest at least 4000 IU daily for maintenance (but some people need much more).
- Exercise: Regular exercise could help increase SHBG and reduce free estrogen levels. One study compared sedentary women and women exercising between 3 and 4 days a week and found significant changes in SHBG after a year. Exercise also promotes a healthy weight and helps improve insulin resistance, both essential for maintaining hormone balance.
- CoQ10 and vitamin E: CoQ10 is an antioxidant often used to support fertility for both men and women. One study found that supplementing with CoQ10 and vitamin E supported healthy blood sugar levels and increased SHBG levels in women with PCOS.
- Sex hormone-binding globulin (SHBG) is a transport protein that binds sex hormones like estrogen and testosterone.
- High levels of SHBG can cause low free testosterone and associated symptoms.
- Low levels of SHBG can cause high free testosterone and associated symptoms.
- Supplements and lifestyle habits can support healthy hormones. Still, a holistic approach, including diet, stress, sleep, and supplements, is always my recommendation for optimal balance.
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