Testosterone is a male hormone that is extremely important in general health and fertility. Testosterone can affect energy levels, sex drive, metabolism, erections, and fertility.
The key to understanding testosterone and fertility is to understand where testosterone is produced and how it works in the testicles. There are two main types of cells in the testicles, Leydig cells and Sertoli cells. Leydig cells make testosterone. Sertoli cells make sperm. When the Leydig cells make testosterone, it is in response to a signal from the brain that is carried by luteinizing hormone, or LH. The LH tells the Leydig cells to make more testosterone. When there is enough testosterone LH turns off. When testosterone is low LH turns back on. The amount of testosterone is very high in the testicle because that’s where it is made. Once it gets to the rest of the body it gets diluted. Testosterone levels in the testicle are about one thousand times higher than in the blood. The Sertoli cells that make sperm require this very high concentration of testosterone to produce the sperm cells. When testosterone is low the Sertoli cells can’t make sperm.
Many people, doctors included, see this relationship and think, “Great, if I give this guy more testosterone he’ll make more sperm!” Unfortunately, it doesn’t work this way. When you get testosterone through injections, creams, or other ways it shuts down the body’s natural testosterone production.
What happens in the brain
What happens is that the brain sees the testosterone and decides that no more LH is needed, so LH turns off. When LH is turned off the testicles don’t make any more testosterone. In the blood, the testosterone levels remain normal because of the testosterone he’s taking. But in the testicle, the testosterone level is the same as the blood, which is way too low. Remember, it’s supposed to be one thousand times higher than the blood! Because of this the Sertoli cells stay turned off, and no sperm are made.
How to boost testosterone without testosterone
Alternative options that turn up the LH system are available. Those medications, such as HCG and Clomid, can cause testosterone levels to go up in a more natural way. This allows the Sertoli cells to ramp up sperm production.
Not everyone on testosterone will have infertility, but it can be a major contributing factor. In general, it should not be used to treat infertility.