Men who carry their mobile phone in a trouser pocket or talk on it for just an hour a day risk suffering with fertility problems, scientists warn.
Research shows that sperm count can also be reduced by talking on a phone that is charging, or even keeping it close by on a bedside table at night.
The quality of sperm among men in Western countries is steadily decreasing, and is considered the factor in 40 per cent of cases in which couples have difficulty conceiving a child.
Heat and electromagnetic activity which emanate from a mobile phone are thought to be ‘cook’ sperm, causing them to die.
The findings have led to a leading British fertility expert to warn men about the risks of being ‘addicted’ to mobile phones.
Israeli scientists monitored 106 men attending a fertility clinic for a year.
The study revealed that men who chatted on the phone for more than an hour daily were twice as likely to have low sperm quality as those who spoke for less than an hour, while those who talked on the phone as it charged were almost twice as likely to suffer problems.
It also found that 47 per cent of men who kept their phones within 20 inches of their groin had sperm levels that were seriously affected, compared with just 11 per cent of the general population.
The findings, published in Reproductive BioMedicine, support a long-feared link between dropping male fertility rates and the prevalence of mobile phones.
Professor Martha Dirnfeld, of the Technion University in Haifa, which carried out the study, said: ‘The [sperm] levels were down to a number that would make conception difficult.
‘If you are trying for a baby and it doesn’t happen within a year you might want to think of whether it could be your mobile phone habit that is to blame.’
Professor Gedis Grudzinskas, a fertility consultant at St George’s Hospital, London, said: ‘Men need to think about their well-being and try to stop being addicted to their phones.’
The study concludes that men planning to conceive should turn off their devices while charging, or keep it at least 20 inches from the groin.