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What Causes Low Testosterone?

Published on Dec 21, 2010

You probably know the important role testosterone plays in a man’s life. It’s the stuff that makes a man a man, from facial hair and a deeper voice to sex drive, erections, and sperm production. When a man has low testosterone, his libido can plummet, along with other aspects of his sexual function.

So you might wonder what causes low testosterone. And is there anything you can do to maintain your testosterone levels, even as you age?

Let’s define what we mean by low testosterone. Testosterone is measured with a simple blood test. Most healthy adult men have testosterone levels between 270 and 1,070 nanograms per deciliter (ng/dL). 300 ng/dL is usually the threshold for a low testosterone diagnosis.

But keep in mind that a man’s testosterone levels fluctuate during the day. Levels are usually highest around 8 a.m. and lowest around 9 p.m. Most doctors conduct testosterone tests early in the morning so they can get a consistent reading over time.

Another thing to think about is the way testosterone is produced. Most of it is made in the testes, but before that even happens, signals from the pituitary gland and the hypothalamus (a part of the brain) need to trigger that production. The pituitary gland and hypothalamus are just as important as the testes.

Now, let’s look at some of the reasons behind low testosterone.

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