Men take note: Storing your cellphone in your pants pocket may result in impaired sperm movement, a controversial new study suggests.
In the study, men who were exposed to more radiation from cellphones were less likely to have normal sperm movement (a characteristic linked to fertility), compared with men who were exposed to very little radiation from cellphones.
"Given the enormous scale of mobile phone use around the world, the potential role of this environmental exposure needs to be clarified," study researcher Fiona Matthews, of the University of Exeter in the United Kingdom, said in a statement. "This study strongly suggests that being exposed to radio-frequency electromagnetic radiation from carrying mobiles in trouser pockets negatively affects sperm quality." [Sexy Swimmers: 7 Facts About Sperm]
However, experts are skeptical of the results, and say that more research is needed to determine the effect of cellphone radiation on sperm.
Cellphones emit electromagnetic radiation in the form of radio waves. Scientists already know that radiation from sources like UV light and X-rays are harmful in large doses. But radio waves from cellphones give off a different kind of radiation and scientists are still unsure of the health risks. Some studies have shown that radiation from cellphones is linked to health problems such as headaches, high blood pressure, an increased risk of developing certain kinds of cancer and reduced male fertility.
In the new analysis, the researchers tested the relationship between cellphone use and male fertility by examining 10 studies involving about 1,500 men. The studies measure "sperm quality" by looking at three characteristics: motility (ability to swim toward the egg), viability (how many sperm were alive in a given semen sample) and concentration (how many sperm were in a given semen sample). The team then separated the studies into two groups: men who used their cellphones less than 1 hour per day (or semen samples exposed to radiation less than one hour in the lab ) and men who used their cellphones more than 1 hour per day (or semen samples exposed to radiation more than one hour in the lab.)
In total, 50 to 85 percent of sperm showed normal movement. But among men who were exposed to electromagnetic radiation from mobile phones, the range was 8 percent lower: 42 to 77 percent of the men had sperm with normal movement. Sperm viability also dropped by 9 percent among men who were exposed to electromagnetic radiation from mobile phones. Sperm concentration did not seem to be affected.
The researchers suggested that heat generated by electromagnetic radiation could be a factor. In a man's pocket, a phone that is giving off heat could raise the temperature of his testes. Studies have shown that increases in scrotal and testes temperature can negatively affect sperm quality.
Exposure to electromagnetic radiation can also generate chemicals called reactive oxygen species (ROS), and too many of these chemicals in cells can lead to DNA damage.
However, Dr. Andrew Kramer, a urologist at the University of Maryland Medical Center, said that he is "not convinced this is good science."
"This is more of them playing off a captive audience," Kramer said. "Men are going to pay attention to news about sperm because it's something they obviously care about."
Kramer said the problem is that a man's sperm count fluctuates all the time. In order for a study like this one to provide compelling evidence, researchers would need to take three or four initial semen samples from men, isolate those men from all other exposures except cellphone radiation, and then take three to four additional semen samples to use as a comparison.
Further, Kramer said sperm quality is difficult to accurately measure in the lab and is skeptical of how much these samples can tell scientists about a man’s fertility. Men are likely nervous and uncomfortable in a lab setting and consequently are likely produce different quality semen than they would during intercourse.
Madhukar Dama, an assistant professor at the Institute for Wildlife Veterinary Research, said that he "strongly believes cellphones could harm sperm and reduce fertility." However, he added that the studies that involved exposing a semen sample directly to radiation should be interpreted with caution.
"It must be remembered that in real life condition, a layer of skin, muscles and fat forms a barrier between cell phone and sperms," Dama told Live Science.
More research is still needed to assess how much influence cellphone radiation is really having on sperm quality, and what role cellphone exposure time might play. The study was published today (June 11) in the journal Environment International.
Editor's note: This article was updated on June 12 to include quotes from professor Dama.
Follow Kelly Dickerson on Twitter. Follow us @livescience, Facebook & Google+. Original article on Live Science.