STEP 5A. Find if you have one of the less well-known causes of low testosterone:
So you found out you are low testosterone or hypogonadal, eh? A natural question for many men is:
"What in the world caused this? What happened to me??"
Sometimes wives and girlfriends are wondering the same thing!
It turns out that is not as easy to answer these kind of questions as you might think. For example, it is rare for someone to come to the Peak Testosterone Forum and have any idea what caused their low testosterone. Occasionally, someone has taken steroids or a "prohormone" that has left them without testosterone and the answer is obvious. Or perhaps a man has a brain injury and suddenly develops low testosterone symptoms, indicating a damaged pituitary or other CNS issues. These situations are fairly obvious and are not what I am going to discuss here.
What is very important to look at are the cases that might escape a physician's eye, because he/she 1) is not looking or 2) is ignorant. And this is case (much) more often that not on forum and, as I will show below, this can in some cases have detrimental outcomes. When one develops hypogonadism, there are many things that should be checked:
1. Empty Sella Syndrome. This is a fairly common problem with the pituitary where the size of the pituitary is greatly decreased due to injury, a tumor, anatomical injury, etc. One study looked at men with erectile dysfunction and low testosterone levels and found that 6.7% of them likely had empty sella syndrome.  Yet another study looked at men with low testosterone and found a still higher percentage: 17.6%.  Of course, empty sella will lead to secondary hypogonadism because of improper signalling from the pituitary, since it is the pituitary that actually signals the testes to produce testosterone.
It should be noted that sometimes it can be better termed "partially empty sella," because some of the gland still remains. However, still other times the pituitary is not even visible on the MRI.
2. Micro and Macroadenomas of the Pituitary. Related to #1 are pituitary tumors that can cause empty sella syndrome. In fact, if you read the first study above, you will see that most of the empty sella syndrome cases were related to tumor growth.  Microadenomas were identified in 7.8% of the cases in the second study as well.
3. Prolactinoma. Another reason that larger pituitary tumors can cause hypogonadism is that they frequently raise prolactin levels. A prolactinoma can stay within the sella, the little "pouch" area where the pituitary sits, or can extend out and cause headaches, visual issues and other medical problems. Only about 10% of macroadenomas fall into this category.  If you do have a prolactinoma, it is usually treated with a dopamine agonist which shrinks the tumor substantially and lowers prolactin levels. Sometimes surgery is required however.
By the way, the second study indicates that serum prolactin levels are a good predictor of a macroadenoma. There were actually four men with macroadenomas and 3 of them had prolactin levels > twice the upper limit, which was probably around 30. So, if your prolactin is high, you'll want to discuss it immedialy with your doctor.
4. The Two O's: Overweight and Obese. Fat cells contain aromatase and, as you gain weight, those fat cells enlarge and build up extra aromatase, the enzyme that converts testosterone to estradiol. Yes, that means that an overweight or obese man will tend to have more estradiol, the "bad" estrogen, and less of his precious testosterone. 
And if the free estrogen to free testosterone ratio gets high enough, obesity can actuallycreate a form of secondary hypogonadism and very significantly turn off your testosterone production. Research shows that testosterone may be as much as 2.5 times lower in obese men.  Ouch! Verifying this is the fact that one study found that massive weight loss (57+ pounds) resulted in an average 58% increase in testosterone levels.  If you lose enough weight, it is possible to even double your testosterone.
Even relatively thin guys like myself can benefit: I had accumulated about 10 pounds of visceral fat and dropped most of it off and found that my estradiol levels plummeted. This gave me a much nicer testosterone-to-estradiol ratio, which is very important. (See my link on The Testosterone-to-Estrogen Ratio for other ideas as well.
5. Hemochromatosis. This common genetic disorder affects about 1 in 200 of people of European ancestry.  You have to have two copies to have the potential to develop the disease but 1 out of every 8-10 people are carriers! Persons with hemochromatosis are much more likely to build up iron, which is very hard on the body. The brain, cardiovascular system and liver can all be negatively impacted.
One other thing that can be affected is testosterone. One study found that 6.4% of men with hemochromatosis were hypogonadal.  This may sound like a fairly low percentage, but keep in mind that they set their definition of hypogonadal at the incredibly low of about 4.1 nmol/l. This translates to about 120 ng/dl in our units here in the U.S., which is about a third of LabCorp's current threshold! So the reality is that a very significant percentage of men with heriditary hemochromatosis likely have low testosterone.
Other common symptoms include:
If you have low testosterone symptoms and some of these other standard symptoms, talk to your doctor.
6) Stress. There have been reports that very high levels of stress can induce a type of hypogonadism. One study looked at this by giving men high doses of hydrocortisone (cortisol) and, sure enough, testosterone came crashing down.  Animals studies have shown that one way this occurs is through an enzyme called 11ï¿½HSD-1 that, under normal circumstances, keeps your cortisol from hammering your testosterone levels. Extreme stress, however, can overwhelm 11ï¿½HSD-1 with too much cortisol and result in a kind of hypogonadism. 
7) Zinc Deficiency. One study took young men (average age 27.5) and then artificially created a zinc deficiency in them by putting them on a zinc-restricted diet. Serum testosterone fell like a rock after 20 weeks from 1173 ng/dl to 311 ng/dl! The same study showed testosterone doubling in those who were only mildly zinc deficient. See my link on Zinc Deficiencies and Low Testosterone for additional information.
8) Weight Loss and Intense Exercise. My page A Protocol to Lose Weight Rapidly and Maintain Muscle discusses a study where the male participants were able to do something remarkable: they combined a wide variety of intense exercises with a 40% reduction in calories and lost 11 pounds and either maintained or even gained some muscle. This is not an easy thing to do and so I did a page covering the subject for men that are interested in short term, accelerated weight loss.
However, one of the guys on the Peak Testosterone Forum noticed that the testosterone levels of the men in the study dropped from 507 to 126 ng/dl! That is a severe fall in testosterone and left those men deep in hypogonadal territory. Of course, the moral of the story is that you can powerfully suppress your body's testosterone production with such a stressful weight loss and thus it may not be appropriate for anyone except men on testosterone therapy, whose levels are held fixed through the administration of exogenous T.
9) Kallman's Syndrome. Kallman's syndrome is basically hypogonadism that usually affects puberty with an accompanying lack of sense of smell. It is fairly rare, but when you aggregate it with other similar conditions that result in low LH/testosterone going through puberty, it is probably around 1 in every 5,000 males. Delayed puberty and small testes/penis are common accompanying symptoms as well. HH (hypergonadotropic hypogonadism) is the broader term and we had one man who was diagnosed with the same. He wrote:
"I like probably many people on this forum had unusually low sex drive for several years, and kept getting told my T was "normal" consistently testing in the 320-330 range. i finally did research and discovered that is not at all normal for someone in their 30s who is otherwise very healthy and who lifts heavy weights 3-4x/week. so i went to an endo and got complete tests w/pituitary MRI done and he agreed my T was low. he asked what treatment options i was interested in, and i said HcG looked interesting to me because i still wanted to have children. he said there is also clomid to consider. when i went back for results he said i had "abnormally normal" LH levels, in other words that i should have a natural pituitary response to produce more LH given my testosterone levels and that was not occurring. otherwise my system was functioning fine. he even diagnosed me with HH as a result. (i also have a weak but not nonexistent sense of smell, and my belief is that i have a milder form of kallmans syndrome, as although i went through puberty on time, i never grew much bodily hair and was a very scrawny kid until i hit the weights hard in my 20s. i think it doesn't get called Kallmans by the medical profession because it is rare and doesn't get diagnosed since puberty occurs)". 
10) Klinefelter's Syndrome. This surprisingly common genetic condition, where a male ends up with an extra X (female) chromosome, affects up to 1 in 500 males.  (Concerning is the fact that one 2007 study found that one type of Klinefelter's seemed to be dramatically increasing in prevalence, so this may be an issue for an ever increasing number of young men.) Sometimes it is "obvious" that there is an underlying condition due to symptoms such as undescended testicles. However, that is not always the case with Klinefelter's and symptoms are less severe. In these cases, many boys are never diagnosed with the condition and limp into early adulthood. There are many common symptoms that often affect someone with Klinefelter's, including a characteristic pear-like body shape, gynecomastia, slow motor development, social awkardness and the like. In addition, a man with Klinefelter's is frequently hypogonadal. The good news is that hypogonadal Klinefelter's males respond well to HRT treatment, at least according to a couple of studies. 
11) Sickle Cell Disease. Studies show that this disease can lead to low testosterone. One small study of men with sickle cell found that 24% of them had low LH and FSH and, therefore, were likely secondary hypogonadal. The authors concluded that it was not due to ferrtin (tissue iron) levels. 
12) The Perfect Storm. Now this model, that I call the "Perfect Storm", is, admittedly, speculation on my part. First of all there are several quite common underlying issues with men that can lower testosterone in the 30% range, which I cover in various place on my site. This is not an exhaustive list, but here are a few:
a) Vitamin D Deficiency. (See my link on Testosterone and Vitamin D for more details.)
b) Varicocele. (See #11 in my link on Improving Male Fertility.)
c) Apnea. (See my link on Apnea and Testosterone for details.)
d) Depression. (See my link on Testosterone and Depression for additional details.)
e) Mercury. (We have had a few men write into the Peak Testosterone Forum who have been eating fish every day or nearly every day, not realizing that, depending on the type of fish, they could be poisoning themselves with methylmercury. See my link on Fish Safety.)
In addition, we already mentioned above other T-related factors, including stress and being overweight. Simple lack of sleep could do it as well. Basically, I cannot help but wonder that if a man has 2 or 3 of these issues, which would not be terribly uncommon, that he could get a combined effect and perhaps drop his testosterone 50% or more? As far as I know, no study has looked at the combined effects of one or more of these testosterone-lowering issues, but it certainly could happen. In this case, it is prudent to troubleshoot each individual issue and get to the root cause.
13) Concusssions and Head Injuries. It is very likely that head injuries can lead to hypogonadism and complete dysregulation of the HPA axis. We had an ex-athlete discuss his battle with just this phenomenon, and you can read the interview I had with him on this page called Testosterone and Concussions.
14) GI (Gut) Issues. This is one I cannot prove, but is just common sense: GI or gut issues likely lower testosterone significantly. The reason I say this is that certain nutrients (Vitamin E, Vitamin C, magnesium, zinc, etc.) all play a role in the body's production of testosterone. Therefore, anything that significantly affects your absorption of these same nutrients can likely lower testosterone levels. And this is important, because there are a host of GI issues that affect men in modern societies: atrophic gastritis, IBS, ulcerative colitis, Crohn's, diverticulis, etc.
15) Parasites. We had one low testosterone man on the Forum of who found that he had a parasite (a tapeworm) and then erradicated it only to find that he felt much better and his testosterone climbed significantly. See my page on Testosterone and Parasites for his story.
16. Overtraining. This ties in with #6 and #8 above. If you overtrain long enough, it is a HUGE stressor for the body and brain. Your immunity is suppressed, your adrenal hormones end up fried, your libido and erections are negatively impacted and testosterone can be lowered as well. See my pages on Testosterone and Overtraining and The Best Signs of Overtraining for some information.
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2) The Journal of Urology, Sep 2003, 170(3):795-798, "The Value Of Pituitary Magnetic Resonance Imaging In Men With Hypogonadism"
3) The Journal of Clinical Endocrinology & Metabolism, Aug 1 2007, 92(8):2861-2865, "Long-Term Management of Prolactinomas"
4) Medical Hypotheses, April 1998, 50(4):331-333, "The role of estradiol in the maintenance of secondary hypogonadism in males in erectile dysfunction"
5) International Journal of Impotence Research, 2003, 15:38ï¿½43, "Oestrogen-mediated hormonal imbalance precipitates erectile dysfunction"
6) Med Hypotheses, 1998 Apr, 50(4):331-3, "The role of estradiol in the maintenance of secondary hypogonadism in males in erectile dysfunction"
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8) The Journal of Clinical Endocrinology & Metabolism, May 1 1988, 66(5):1019-1023, "Effect of Massive Weight Loss on Hypothalamic Pituitary-Gonadal Function in Obese Men"
10) The Journal of Clinical Endocrinology & Metabolism, Apr 1 2005, 90(4):2451-2455, "Hypogonadism in Hereditary Hemochromatosis"
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15) Clinical Genetics, April 1988, 33(4):262ï¿½269, "Follow-up of 30 Klinefelter males treated with testosterone"