High SHBG Levels Can Inhibit Muscle Growth

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by Josh Hodnik

Sex hormone binding globulin (SHBG) is a protein present in the human body that sex hormones, such as testosterone and estradiol, often bind to before entering the bloodstream. When a discussion occurs involving androgens or estrogen, rarely does SHBG fall into the conversation. However, the fact is, this substance plays an important role in how efficiently many hormones are utilized in the body.

SHBG is a glycoprotein that binds to, transports, and inhibits the function of testosterone. Its often thought that SHBG transports and protects testosterone from being eliminated too quickly. When testosterone is bound to SHBG, it becomes useless. In this state, testosterone is not active or bioavailable. Because testosterone doesn’t normally break free from SHBG, and is not active when bound, viewing SHBG as a protein that protects and transports testosterone is pointless. SHBG can be legitimately viewed, as is a protein that serves the purpose of keeping hormone levels in balance in within the body.

Normally, 45% of total testosterone is bound to SHBG, 53% is bound to albumin, and 2% is unbound and active. This is referred to as free-testosterone. Unlike testosterone that is bound to SHBG, albumin-bound testosterone can break free and become free fairly easy. An individual that has normal testosterone levels and high SHBG levels can experience the same symptoms that occur in men with low-testosterone. Since testosterone that is bound to albumin will eventually become active, free and albumin-bound testosterone should be taken into account when evaluating testosterone levels instead of total testosterone.

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SHBG safeguards the body against hormone levels. In the womb low levels of SHBG are present to allow activity of sex hormones. This allows formation of sex organs and this is when gender is determined. SHBG levels rise after birth and remain elevated throughout childhood. These levels will drop to half for girls and a quarter for boys during puberty. The decrease of SHBG during pubescent years is caused by an increase in growth hormone. Growth hormone levels will decrease during adulthood and SHBG will rise. Levels normally increase at a rate of 1% per year after early adulthood, resulting in lowered free-testosterone. Add in declining total testosterone levels from aging and the impact can be significant. The 1% yearly increase is just an average, and this can vary significantly from individual to individual. There are many factors that can influence a rise or fall in SHBG levels.

Normal SHBG Levels in Adult Men (nmol/L)
<20 Low
20-60 Normal
>60 High

Increasing SHBG

Estrogen
When steroids are used to effectively build muscle, elevated estrogen levels are always a concern. Anabolic steroids can result in higher estrogen levels in men, and this can lead to water retention, fat storage, and bitch tits. Its vital to keep estrogen levels in a range where muscle growth can occur while not experiencing estrogen related side effects. High estrogen levels come with another side effect that can sabotage muscle growth. As estrogen levels climb, so does SHBG. Even if exogenous steroids are administered, higher than normal SHBG caused by high estrogen levels can have a negative impact on anabolism.

Thyroid
There is a strong relationship between thyroid hormones and SHBG. Hyperthyroidism (condition where too much thyroid hormone is produced) causes SHBG to increase. This can also occur when high levels of thyroid drugs (T-3, T-4) are taken.

Tamoxifen
This serm has been used for decades to lower estrogen levels in men, especially when using anabolic steroids. It is often found in PCT protocols, when attempting to keep estrogen levels in check and to stimulate natural testosterone production. It is effective in lowering estrogen levels, but it also raises SHBG levels when doing so. Raising SHBG levels during PCT can alter the process of recovering hormones to baseline levels.

Other Drugs That Increase SHBG:
Clomiphene, Toremifene. Also, some statins, opiods, beta-blockers, tranquilizers, antidepressants, and antifungals have been shown to raise SHBG.

Decreasing SHBG

Growth Hormone
Growth hormone has been shown to greatly influence SHBG levels. The increase in growth hormone during puberty is what causes the large drop in SHBG, leading to the changes that occur during puberty. A decrease in growth hormone levels seem to run parallel with rising SHBG with age. Taking exogenous growth hormone may be the most effective method for lowering SHBG levels. While growth hormone doesn’t play a direct role in muscle growth, its ability to lower SHBG influences muscle growth indirectly.

Letrozole
This aromotase inhibitor is the most effective for inhibiting estrogen production. Unlike the serms tamoxifen and clomiphene, letrozole does not increase SHBG, but actually decreases it. For controlling estrogen while taking anabolic steroids, letrozole is a good choice as it eliminates estrogen and lowers SHBG.

Other Drugs That Decrease SHBG:
Exemestane, anastrozole, proviron, stanozolol, and insulin.

Sex hormone binding globulin serves the purpose of keeping a hormonal balance. Without it, the changes that take place from childhood to adulthood would not happen in the manner that they should. While this protein does serve a purpose, higher levels during adulthood can greatly impair muscle growth. A simple test can be ordered by a physician to check SHBG levels.  

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