Global sperm counts have been declining for decades, and although researchers have many hypotheses, no one knows exactly why. A new study out of Switzerland may add another potential risk factor to the list: mobile phones.

After analyzing the semen samples of more than 2,800 young men, Swiss researchers found an association between a higher frequency of self-reported mobile phone use and lower sperm concentration in a study published this week in the journal Fertility and Sterility.

They did not find a difference in sperm motility or morphology between the different types of phone users. They also didn't find any evidence indicating that storing the phone in the pocket, rather than in a backpack, for example, plays a role in sperm concentration.

The researchers conducted the study from 2005 to 2018. They found that the association between high phone use and low sperm count was more pronounced during the first years of the study than at the end.

"This pattern is in line with the transition to new technologies, mainly from 2G to 3G and 4G, and the corresponding decrease in the phone's output power," the researchers wrote.

Factors that impact fertility

The study adds mobile phones to a long list of factors that other researchers have found could mess with fertility: smoking, obesity, alcohol, psychological stress and the so-called "endocrine disrupting" chemicals found in pesticides and the plastic wrappers that package the vegetables we buy at the store.

The research provides some evidence to growing concern over the past decades that the radiofrequency electromagnetic fields (RF-EMFs) emitted by mobile phones have a negative impact on human reproductive health.

Up until now, studies looking into this potential association have only been facilitated on mice or on sperm in vitro. This study marks the first facilitated in the "real world", which outside researchers say is positive.

"The study is not perfect, and the authors of it acknowledge that (pointing to self-reporting of mobile phone usage), but it is a study in the real world – and that is good in my opinion," Professor Allan Pacey of Andrology at the University of Manchester, who was not involved in the research, said in a statement.

No explanation of the biology conducted yet

Alison Campbell, the Chief Scientific Officer of Care Fertility, called the study "fascinating and novel." She was not involved in the research.

However, she said, there could be other explanations for the sperm count decline among frequent phone users.

Pacey echoed the same concern: "We cannot be sure that the mobile phone is not a surrogate marker for another aspect of the men's lifestyle or occupation, that is the real cause of any changes to their sperm quality," he said.

Campbell also pointed out that this is just an observed – potential – association.

"There is currently no confirmed explanation of the biology or mechanisms behind this finding, as the research has not yet been done," she said.

What should men do?

If you're a man looking to have kids someday, this news might seem concerning, but researchers say not to worry or make any big changes yet. 

"If men are concerned, then keeping their phones in a bag and limiting their use is a relatively easy thing for them to do," Pacey said. "But there is currently no evidence that will improve their sperm quality (that would need a randomized controlled trial). As for me, I will be continuing to keep my phone in my trouser pocket."

Edited by: Sushmitha Ramakrishnan