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Free Testosterone and SHBG

Some researchers believe that free testosterone is the only testosterone that really counts, since it is the testosterone ready and able to actually "work" on your tissues. And there is a lot of truth to this.  However, other experts counter that total testosterone is really the better number, because it acts as reserve or bank to build from.  Well, I will leave that debate for the men in white, but, in the meantime, it's best to realize that free testosterone is an incredibly important number for men to monitor and maintain. 

So why do some say that free testosterone the only testosterone that does your body any good?  The reason is that about two thirds of non-free, or bound testosterone is actually chemically bonded to a protein called Sex Hormone-Binding Globulin (SHBG) and about 1/3 to a protein called albumin.  Only a small percentage (about 2 percent) is actually free to supercharge our brains, blood, muscles, sex lives and all the other things we associate with testosterone. 

So what then controls your free testosterone? It turns out that your levels of SHBG are actually very important, because, of course, SHBG is what binds to testosterone and can take it "out of commission."  SHBG is controlled and produced in the liver primarily by androgens (and thyroxine).  Normal aging, as many of us know all too painfully, leads to substantial drops in androgens such as testosterone and a corresponding rise in SHBG.  Think how ugly this is:  decreasing testosterone leads to increasing SHBG which leads to decreased free testosterone.  No wonder some of you feel like crap!

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So how do you know if your free testosterone is low?  It starts with a simple test from your doctor.  You sometimes have to ask for this, as some doctors just stick with total testosterone.  Generally, free testosterone is given as a percentage of total testosterone, the typically acceptable range according to the lab listed as 1.5%-2.5%. 

NOTE:  Men on HRT (Hormone Replacement Therarpy or testosterone therapy) will often have an elevated free testosterone percentage, because HRT tends to lower SHBG. Also, some men have low SHBG even before starting HRT. These men often have great difficulty with achieving successful results from testosterone therapy for reasons that are not totally understood.

Let me give you some of the most important ways to control SHBG and Free Testosterone:

1) Estrogen.  You must keep your estrogen levels in check.  Research shows that normal aging as well as an increase in adipose - that's a nice way of saying fat - tissue leads to ever increasing levels of estrogen. And here's the key:  increasing estrogen leads to increasing SHBG.  Please read the important link on How to Control Estrogen.

2) Testosterone.  Low testosterone levels will tend to raise your SHBG as well. Yes, that's called a vicious circle. Read this link on How to Raise Testosterone Naturally if you have not already.

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3) Medications and Alcohol.  Many medications can effect SHBG.  Remember that SHBG is made in the liver and most medications effect the liver.  Common drugs that often raise SHBG are sedatives, antihypertensiaves, tranquilizers as well as your old friends beer and booze.

4) Stinging Nettle. Another way to lower SHBG is through an herb called Stinging Nettle.  Stringing Nettle is widely prescribed in Europe for BPH ( Benign Prostate Hypertrophy). Several studies have documented Stinging Nettle's SHBG-lowering powers [2] and, so far, Stinging Nettle has an excellent safety profile.  However, its side effect profile is worth mentioning:  Stinging Nettle also blocks the action of the enzyme that converts testosterone to DHT.  Some would argue that this is good since DHT is associated with things like hair loss and prostate problems.  However, sometimes, in sensitive individuals, side effects include erectile dysfuntion and a decreased amount of semen. Plus, DHT is a critical androgen for males and very important to libido and so Stinging Nettle is questionable in my opinion because of it. I should point out that there are no studies, as far as I know, that actually show Stinging Nettle increasing free testosterone:  more research needs to be done. 

CAUTION:  What makes me nervous about longer term use of Stinging Nettle is that significantly affects many P450 cytochrome enzyme systems. [5] This is not something to "mess with" as this enzyme system is involved in your steroid hormones and lipids as well.  Now, granted, Stinging Nettle is actually likely to positively affect your T and E2 and has been shown to improve cholesterol levels. However, these P450 enzymes also are involved in detoxification.  Do we know that it will not negatively impact one of these pathways?  In addition, this herb clearly affects many other enzymes, including 5-alpha reductase and possibly aromatase, that have nothing directly to do with the liver enzymes.  Again, how do we know it is not affecting something unanticipated in a negative manner?  That is just my perspective on it, but I tend to be very cautious about herbs and supplements because, over the decades, I have seen so many superstars that have been found to cause unexpected issues.

5) Insulin Resistance.  Insulin resistance will lower your SHBG [1] and, therefore, in the short term probably raise free testosterone. So let's all get insulin resistant and live happily ever after, right?  Wrong!  Insulin resistance is a death warrant.  (Read this link on Metabolic Syndrome for more details.) 

6) Sugar and Corn Syrup.  These bad boys can lower SHBG.  Unfortunately, these can lead to insulin resistance, inflammation, advanced glycation end products and many other nasty things. How does it do all this? Researchers have discovered that sugar will also lower SHBG, because it increases fat synthesis in the liver, which in turn shuts off the gene involved in SHBG synthesis. Bottom line:  stay away from sugar and corn syrup even though in the short term they may raise your free testosterone.

7) Green Tea.  Green Tea does actually raise SHBG. 

8) Vitamin D.  Vitamin D was found in a 2009 study of about 2,300 adult males to lower SHBG and increase both free and total testosterone. [3]

9) Boron (Sodium Tetraborate or Borax). One study showed that boron can not only increase free testosterone but lower estradiol as well.  See my link on Boron and Testosterone for more details.

10) Protein-to-Carbohydrate Ratio.  The protein/carbohydrate ratio has an interesting effect on free testosterone and SHBG.  Several studies have shown that increasing carbs versus protein boosts total testosterone. However, before you start pounding granola bars, one study found that increasing the protein/carb ratio not only increased total testosterone but also SHBG. [4]  This means that free testosterone may not have been increased significantly because of SHBG's opposing effects.  (Increasing the protein to carbohydrate ratio also increased cortisol, a fact I cover elsewhere on this site.)

CAUTION: If you have a medical condition or are on any medications, please discuss any changes with your doctor first. Certain supplements, foods and even juices can alter absorption rates of certain medications for example. Play it safe.


1) J Korean Diabetes Assoc, 1998 Sep,22(3):328-337

2) Planta Med, 1995 Feb, 61(1):31-32; Fortschr Med, Nov 10 1996, 114(31):407-411; Z Naturforsch [C], 1995 Jan-Feb,50(1-2):98-104

3) Clin Endocrinol (Oxf), 2009 Dec 29, [Epub ahead of print], "Association of vitamin D status with serum androgen levels in men"

4) Life Sciences, May 4 1987, 40(18)1761-1768, "Diet-hormone interactions: Protein/carbohydrate ratio alters reciprocally the plasma levels of testosterone and cortisol and their respective binding globulins in man"

5) Phytomedicine, 2003, 10(5):405-15, "Modulatory effect of Urtica dioica L. (Urticaceae) leaf extract on biotransformation enzyme systems, antioxidant enzymes, lactate dehydrogenase and lipid peroxidation in mice"