"Men who talk on their mobile phones for an hour a day 'are twice as likely to have low sperm quality'," the Daily Mail reports.
Is the use of smartphones damaging men's sperm? The quick answer, based on the results of this study, is we don't know.
The men studied were already experiencing fertility problems, and had been referred to a fertility clinic for semen analysis. At the same time, they completed questionnaires on their mobile phone use.
The researchers found a couple of links between mobile phone use and sperm concentration. A greater number of men with abnormal concentration reported speaking on their phone for more than an hour a day, and speaking while their phone was on charge.
There were no links found for other measures of semen quality, and no significant link with where on the body the mobile phone was carried, such as the trouser pocket – despite media headlines to the contrary.
The study has several important limitations, however. This includes assessing the link between semen quality and mobile phone use, so it therefore can't prove cause and effect.
We don't know when the men's fertility problems may have started, or how well the phone use currently reported reflects longer-term use patterns. It is also a very small sample of men.
The researchers recommend carrying your phone in your shirt pocket and using an earpiece when making a call.
However, given that the study analysed both of these factors and found no link with sperm quality, we can't say whether this will have any effect on fertility.
The study was carried out by researchers from the Carmel Medical Center in Israel, and was published in the peer-reviewed medical journal Reproductive BioMedicine Online.
No funding sources have been reported and the researchers declare no conflict of interest.
The UK media has taken the opinions expressed in the study at face value without considering the research's limitations, which, to be fair to the researchers, were highlighted in the study itself.
There are also some factual inaccuracies in the reporting. The Daily Telegraph reported the "sperm levels of men who kept their phones in their pocket during the day were seriously affected in 47% of cases, compared to just 11% in the general population". This is incorrect.
The study actually reports that – of men who carried their phone within 50cm of their groin – 47% of them had an abnormal sperm concentration and 53% had normal concentration.
Of men who carried their phone more than 50cm away from their groin, just 11% had abnormal concentration, with 89% having a normal concentration.
The calculations using these numbers actually found no statistically significant link between the distance the phone was carried from the groin and sperm concentration.
None of the men in this study were from "the general population" – all had been referred to a fertility clinic.
This was a cross-sectional study of a sample of Israeli men referred for semen analysis, who also completed questionnaires on their mobile phone use.
As the researchers say, in around a third of infertility cases, the cause comes down to male-related factors.
Research has demonstrated an overall decline in semen quality over the past 100 years. The researchers suggest one contributing factor is radiofrequency electromagnetic radiation emitted from mobile phones.
A study like this has numerous limitations when it comes to providing evidence. These include the cross-sectional assessment method – which cannot prove cause and effect – the small sample size, and the fact all the men studied were already experiencing fertility problems.
The study included 106 men who received semen analysis as part of their assessment for infertility at an IVF clinic in Israel in 2011 and 2012.
The men completed a questionnaire on sociodemographics, health and lifestyle. Heavy smokers, heavy drinkers and those with health issues thought to possibly affect their fertility, such as diabetes and vascular problems, were excluded. This led to the further exclusion of 26 men, leaving 80 for the final analysis, with an average age of 35 years old.
The men completed questions on their mobile phone use. They were asked about the number of devices used and how long they spent talking on it each day: less than 30 minutes, 30-60 minutes, 60-120 minutes, or more than 120 minutes a day.
They were also asked where they stored the device while talking (for example, the use of hands-free or earphones), carrying or charging. Overall, the researchers classed this as distance from the groin – greater or less than 50cm.
The researchers also asked how long the men had owned a mobile phone, whether they talked on the mobile while it was charging, and whether they talked in low-reception areas such as lifts and underground floors.
Semen quality – volume, sperm concentration, motility (how well they can "swim") and morphology (shape) – were assessed and analysed using standard World Health Organization definitions of normality and abnormality.
The 80 men had owned a mobile for an average of 12.9 years. Most of the men had normal semen volume (86%), sperm morphology (99%) and motility (71%), and just over half had normal sperm concentration (57%).
Sperm concentration was the only measure that found significant links with mobile usage. Significantly more men with abnormal concentration spoke on the phone for more than an hour a day (61%) compared with those with normal concentration (39%).
Significantly more men with abnormal concentration reported speaking while their device was on charge (two-thirds versus one-third of those with normal concentration).
There was no significant link between sperm concentration and other factors, including the distance from the groin the mobile was carried, speaking in low-reception areas, or use of hands-free.
Aside from mobile use, there was a significant link between sperm concentration and smoking. Significantly more men with abnormal concentration had smoked (57% currently or in the past) compared with those with normal concentration (43%).
Data is not given for semen volume and sperm motility, but the researchers say there was no significant difference in mobile phone use between those with normal and abnormal measures.
The researchers concluded that, "Our findings suggest that certain aspects of cell phone usage may bear adverse effects on sperm concentration. Investigation using large-scale studies is thus needed."
This cross-sectional study included just 80 Israeli men who were already experiencing fertility problems and had been referred for semen analysis. The men answered questions on their mobile phone use at the same time.
The research found a couple of links with sperm concentration – a greater number of men with abnormal concentration reported speaking on their phone for more than an hour a day, and speaking while their phone was on charge.
There were no links seen with semen volume and sperm motility. Sperm morphology couldn't be assessed because only one man had abnormal morphology.
The study has a number of important limitations, which means it can tell us very little about whether there could be a link between radiofrequency electromagnetic radiation and semen quality.
The study assessed semen quality and mobile phone use at the same time, and this can't prove cause and effect. Though the men could be said to be reporting on past use, we don't know when their fertility problems may have started – for example, how long they had abnormal concentration for – or how well the phone use reported reflects longer-term use patterns.
For example, if the men report speaking on their mobile phone for more than an hour every day or speaking while the phone was on charge, we don't know whether this is something they do occasionally or whether they have done this every single day for a number of years.
It was a very small sample of only 80 men, which means there are smaller numbers when splitting them into normal or abnormal factors of semen quality, and this increases the possibility that you find links by chance. You are likely to get more reliable links if looking at a sample of 800 or 8,000 men, for example.
This is also a specific population sample of Israeli men who may have different health, lifestyle and environmental influences from other populations, meaning you can't easily transfer the results.
Other limitations, which the researchers acknowledge, include the different types of devices used – which may emit different amounts of radiofrequency electromagnetic radiation – and the distance from mobile phone towers.
Ideally, you would need a cohort study that prospectively assesses the long-term mobile phone use of a large sample of young men who start off with healthy semen. There are, however, likely to be various logistical issues with such a study.
Evidence does suggest sperm quality has dropped over the past few decades. The now ubiquitous use of smartphones in developed countries, and the corresponding exposure to radiofrequency electromagnetic radiation, could be one factor.
Other suggestions include poor diet and exposure to artificial hormones like oestrogen. One well-established link – which the study did find – is smoking.
Overall, the question of whether mobile phone use and exposure to radiofrequency electromagnetic radiation could be having an adverse effect on male fertility is an important one, but it cannot be answered by this study.