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. 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. Therefore, according to one school of thought, 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.
Well, kind of.
It turns out that the testosterone bound to albumin is actually only bonded loosely and is readily available to do work on your tissues. In fact, researchers have come up with the following formula:
And they point out that it is really bioavailable testosterone that is the true free testosterone. Furthermore, still 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 what then controls your free testosterone? It turns out that your level of albumin is relatively fixed with minimal fluctuation in most men. However, SHBG can vary widely and lab results clearly show that as SHBG goes up, the percentage of free testosterone as a percentage of total goes down and, as SHBG goes down, the percentage of free testosterone goes up. Thus, it is SHBG that has tremendous control over free testosterone.
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. And, practically speaking, low free testosterone levels will yield low testosterone symptoms just as surely as low total testosterone will.
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 10 Natural Ways to Lower SHBG and Raise Free Testosterone:
1) Testosterone and Lowering Estradiol. On this page, I'll show some ways to uniquely raise free testosterone levels. However, the most straightforward way to raise free testosterone levels is by raising total testosterone levels. In general, as you raise total testosterone, free testosterone tends to rise with it. I have already created a page with 40+ Ways to Raise Testosterone Naturally. Again, though, on this page we'll look at some ways to raise your percentage of free testosterone (out of total testosterone).
Similarly, if you can lower your estradiol levels, you can generally get a boost in total and free testosterone. 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 the estrogens. And here's the key: increasing estrogen leads to increasing SHBG, which will lower your free testosterone as a percentage of your total. Please read the important link on How to Control Estrogen.
2) 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.  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.)
3) DHEA. Researchers examined untrained young and middle males and found that giving them 50 mg of DHEA daily raised their free testosterone significantly. They also noted that normally HIIT substantially lowers testosterone, but with the DHEA no such decrease in free testosterone at least occurred.  There are warnings out there that DHEA can increase estradiol disproportionately, but I have seen no actual research evidence of this. The real concern with DHEA is more brain-related. Ray Peat, in particular, has noted:
"One study has found that the only hormone abnormality in a groupt of Alzheimers patients' brains was an excess of DHEA. In cell culture, DHEA can cause changes in glial cells resembling those seen in the aging brain. These observations suggest that DHEA should be used with caution. Supplements of pregnenolone and thyroid seem to be the safest way to optimize DHEA production." In spite of this, DHEA seems to be widely used in the alternative and anti-aging communities. Do your own research and talk to your doc is all I can say.
CAUTION: Low SHBG men should not lower their SHBG further. See my page on The Risks and Causes of Low SHBG for more information.
4) Medications and Alcohol. If you have high SHBG and low free testosterone, one of the first checks you should do is looking at any prescriptions that you have: 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 alcohol.
5) 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  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.
6) Tongkat Ali (LJ 100). One study of a specific extract (LJ 100) of Tongkat Ali found that "SHBG decreased 66%, and the Free Testosterone Index escalated 73%."  I have seen claims that LJ100 is the only extract that it standardized for a high percentage of eurypeptides, the ingredient responsible for the above. CAUTION: Tongkat Ali can raise IGF-1 and should be monitored in those 40+ in my opinion: you do not want to be too high in this hormone, as it is associated with prostate and other cancers. (Being too low has been identified with increased cancer risk.)
7) Boron. This supplement produced a significant drop in SHBG in a recent study, which lead to a 28% increase and 39% drop in free testosterone and total estradiol, respectively.  This is a nice change in the testosterone-to-estradiol and should help a guy feel significantly better. See my link on Boron and Testosterone for more details.
Did you know you can inexpensively do your own testing for many hormones? The industry leaders is Discounted Labs..
8) Insulin Resistance. Insulin resistance will lower your SHBG  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.)
9) 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.
10) 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. 
11) Magnesium. Research shows that magnesium can bind to SHBG and give a man a little higher bioavailable and free testosterone. I doubt this is a big effect, but it's cheap and easy to try. See my page on Testosterone and Magnesium for more details.
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