A global decline in semen quality has been observed over the last 50 years.
Various environmental and lifestyle factors have been proposed to explain the issue, but the role of electromagnetic radiation emitted by mobile phones had yet to be demonstrated, until now.
Researchers from the University of Geneva (UNIGE) analysed data from 2,886 Swiss men aged 18 to 22, recruited between 2005 and 2018 at six military conscription centres.
They found that sperm concentration was significantly higher in the group of men who did not use their phone more than once a week (56.5 million per millilitre), compared with men who used their phone more than 20 times a day (44.5 million per millilitre).
According to the study, this difference corresponds to a 21% decrease in sperm concentration for frequent users, those who used the devices more than 20 times a day, compared to rare users, those who used their phone less than once, or once a day.
Semen quality is determined by the assessment of factors such as sperm concentration, total sperm count, sperm motility (movement) and sperm morphology (shape).
The study did not find any association between use of the devices and low sperm motility or unusual morphology.
The World Health Organisation (WHO) sets out that a man will most probably take more than one year to conceive a child if his sperm concentration is less than 15 million per millilitre.
Additionally, the likelihood of pregnancy will decrease if the sperm concentration is below 40 million per millilitre.
Past studies have shown that semen quality has decreased over the last 50 years, with a combination of environmental factors (pesticides, radiation) and lifestyle habits (diet, alcohol, stress, smoking) thought to be contributors.
This association found in the study was more pronounced in the first study period (2005-2007) and gradually decreased with time (2008-2011 and 2012-2018).
The findings also indicate that 4G may be less harmful than 2G.
‘This trend corresponds to the transition from 2G to 3G, and then from 3G to 4G, that has led to a reduction in the transmitting power of phones,’ said Martin Roosli, associate professor at Swiss Tropical and Public Health Institute (Swiss TPH).
Co-leader of the study Rita Rahban, a senior researcher at the UNIGE and at the Swiss Centre for Applied Human Toxicology (SCAHT), said: ‘Previous studies evaluating the relationship between the use of mobile phones and semen quality were performed on a relatively small number of individuals, rarely considering lifestyle information, and have been subject to selection bias, as they were recruited in fertility clinics.
‘This has led to inconclusive results.’
The research, conducted in collaboration with the Swiss TPH, also indicates that where the phone was kept – such as trouser pockets – was not linked to the lower concentration and count levels.
However, the number of people who said they did not carry their phone close to their body was too small to draw a firm conclusion on this point.
The men in the study completed a detailed questionnaire related to their lifestyle habits, their general health status, the frequency at which they used their phones, as well as where they placed them when not in use.
Despite the findings, published in the journal Fertility and Sterility, experts say there is no cause for alarm.
Professor Alison Campbell, chief scientific officer of the Care Fertility Group said: ‘This is a fascinating and novel study which should not cause alarm or drastic changes in habits.
‘Men looking to conceive, or wanting to improve their sperm health should exercise – but not overheat in their groin area – eat a balanced diet, maintain a healthy weight, avoid smoking and limit alcohol and seek help if they are having problems conceiving.’
Allan Pacey, professor of andrology at the University of Manchester, said: ‘If men are concerned, then keeping their phones in a bag and limiting their use is a relatively easy thing for them to do.
‘But there is currently no evidence that will improve their sperm quality. As for me, I will be continuing to keep my phone in my trouser pocket.’