[Lotus]

SHBG: The Master Regulator for Testosterone and Estrogen

SHBG is a protein produced primarily in the liver, although the testes, uterus, brain, and placenta also synthesize it. It serves as a transport carrier, shuttling estrogen and testosterone to sex hormone receptors throughout your body.11,12 SHBG also safeguards these vital hormones from degrading too rapidly and prevents their clearance from the body.

It thus acts as the master regulator of your sex hormone levels, maintaining the delicate balance between estrogen and testosterone critical to overall health in aging humans.

New evidence further indicates that the SHBG molecule itself plays another key role in the body: conveying essential signals to the heart, the brain, and adipose (fat) tissue that ensure their optimal function.13 There’s even a special SHBG receptor molecule on cell surfaces that functions much like the ubiquitous vitamin D receptor protein, helping cells communicate with one another.14,15 In other words, SHBG itself functions much like a hormone.

Knowing your SHBG levels, along with testosterone and estrogen, thus gives you and your doctor a more precise picture of your overall health—and enables you to take preventive measures against life-threatening conditions for which you may be at greater risk.

Aging Humans and Increasing SHBG: An Overlooked Threat

As you age, SHBG levels may steadily rise, even though your production of sex hormones continues to decline.8,16 The result? SHGB binds to what few sex hormones you have remaining and reduces their bioavailability to cells in your body.

With elevated SHBG in the blood, too much testosterone may be sequestered and thus functionally unavailable to healthy tissues. Because testing for SHBG is largely overlooked, many older men (and their doctors) may be led to believe through standard testing that they have “normal” total testosterone levels—but since most of it may be bound to elevated levels of SHBG, in actuality they may be testosterone deficient.16

Why? Testosterone, like all steroid hormones, is derived from cholesterol, a fat molecule.16 Fats don’t dissolve in water, so the amount of testosterone floating freely in your bloodstream is small (about 0.5-2% of the total amount).16,17 Most of the circulating testosterone in your blood is either bound to the protein albumin or to SHBG.18-20

It is the combination of free and albumin-bound testosterone that ultimately determines your bio-available testosterone status.16,21-24

As a result of imprecise testosterone measurement, aging men may experience signs of feminization as their increased SHBG binds testosterone, preventing testosterone from exerting its effects and leaving estrogen’s physiological impact on the male physiology unchecked.16 These may include gynecomastia (the development of fatty breast tissue in men), diminished libido and poor sexual performance, cognitive decline, and chronic fatigue.

Combating Metabolic Syndrome

While excess SHBG creates problems with sex hormone balance, having SHBG levels that are too low is associated with other disorders. Nowhere is the impact of low SHBG so profound as in the cluster of conditions known as the metabolic syndrome, which encompasses obesity, insulin resistance, lipid abnormalities, and chronic high blood pressure.9

In men, low total testosterone and low SHBG are predictors for a higher incidence of metabolic syndrome and many of its components.9,25-29

In late postmenopausal women, low SHBG and high estrogen levels correlate with the inflammatory state associated with metabolic syndrome.30 SHBG abnormalities have also been linked to an increased risk of acne, infertility, polycystic ovary syndrome, and uterine cancer in overweight women.6,31-33

The high insulin levels found in people stricken with metabolic syndrome have also been shown to suppress SHBG, creating a vicious cycle of abnormal SHBG activity.34,35

The good news is that testosterone supplementation for men, and bioidentical hormone replacement for women, may safely and effectively reverse many of these adverse, age-related metabolic changes.36,37 Obtaining accurate measurement of sex hormone levels through SHBG blood testing thus enables you and your doctor to prevent or combat common medical disorders.

Low SHBG Is a Key Marker of Cardiovascular Disease

SHBG levels have an important relationship with nearly every biomarker of cardiovascular disease, from C-reactive protein (CRP) to arterial calcification.38,39 Low SHBG is also associated with elevated triglycerides and low-density lipoprotein (LDL).40

Calcification of blood vessels, an early finding in cardiovascular disease, is also associated with lower SHBG levels, especially in women.10,38 Low SHBG in women is associated with higher levels of C-reactive protein (CRP), an important marker of inflammation and cardiovascular risk.39 In men, low SHBG indicated an increased risk of death from cardiovascular disease.35 In both men and women, low SHBG levels are strongly correlated with obesity.41

SHBG, alone and in the context of specific sex hormone levels, thus constitutes an integral predictor of a major chronic age-related condition. Some experts are now recommending SHBG measurements as another means of evaluating cardiovascular and metabolic risk.42

http://www.lef.org/magazine/mag2011/may2...tus_01.htm