Causes of Low Testosterone
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.
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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:
Bronze skin color
Low of body hair
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 11ßHSD-1 that, under normal circumstances, keeps your cortisol from
hammering your testosterone
levels. Extreme stress, however, can overwhelm
11ßHSD-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.
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.
1) The Journal of Urology, Feb 1996, 155(2):529-533, "Prevalence of
Hypothalamic-Pituitary Imaging Abnormalities in Impotent Men with Secondary
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, 15:38–43,
"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"
7) The Journal of Clinical Endocrinology & Metabolism, Dec 1 1977,
45(6):1211-1219, "Low Serum Testosterone and Sex-Hormone-Binding-Globulin in
Massively Obese Men"
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"
11) Clin Endocrinol Metab, 1983 Sep, 57(3):671-3, "Acute suppression of
circulating testosterone levels by cortisol in men"
12) J Androl, 1997, 18:475-4791997, 18:475-479
13) Acta Haematol, 2012;128(2):65-8, "Hypogonadism in patients with sickle cell
disease: central or peripheral?"
14) European Journal of Human Genetics, 2008, 16:163–170, "Is the prevalence of Klinefelter syndrome increasing?"
15) Clinical Genetics, April 1988, 33(4):262–269, "Follow-up of 30 Klinefelter
males treated with testosterone"