Researchers who studied the effects of mobile phones on men found that those men who are spending many hours talking on their cell phones may have impaired sperm counts.

The researchers believe that it could be radiation or the heat that are affecting both quantity and quality of the sperm.

Three hundred sixty-four men who were evaluated in the fertility clinics were organized into three different groups according to their sperm count.
Then they realized that men from the normal sperm count group had different levels of sperm according to the amount of time they spent talking on their mobile phones. The study showed that men who did not use a cell phone at all averaged 86 million per milliliter, with 68% motility and 40% being in normal form. On the other hand, men who talked for more than four hours a day averaged 66 million sperm per milliliter, with 48 % motility and 21 % taking normal form.

Although all the data is indicating a strong association between mobile phone use and decreased fertility, it was impossible to determine what exactly has been leading to diminished sperm levels.

Animal studies showed that it could be the heat cell phones have on the tissue or electromagnetic fields damaging Leydig cells in the testes. However, this would only be possible if cell phones were held anywhere near the crotch. Otherwise this should not be the case.
More and larger studies need to be done in order to understand the causes cell phones have on sperm production.