Hours of chatting on a mobile phone are suspected to be slashing male fertility around the world, new research shows.

Men who use mobile phones for more than four hours a day produce fewer and poorer quality sperm, according to results of a study released at an American Society for Reproductive Medicine conference in New Orleans.

London’s Daily Mail reported that doctors think sperm counts and quality might be damaged by electromagnetic radiation emitted by handsets or the heat they generate.

The Independent said the study suggested that microwaves from mobiles appear to reduce the number, mobility and quality of sperm by almost half, to the point at which some men might become infertile.

Sperm from heavy mobile users had a 30 per cent drop in the capacity for movement and viability when compared with sperm from men who did not use a mobile phone, The Guardian reported.

The findings come at a time when many nations are asking why the fertility rates in their male populations are falling.

Almost 1 billion people around the world use mobiles and in some countries the number is growing at 20 to 30 per cent a year, The Independent said.

The Guardian said the study was too preliminary to prove an unequivocal link between mobile phones and falling sperm counts.

However, it said scientists want to look at mobile usage taking into account other factors such as age, weight, smoking, stress and whether people have sedentary jobs.

Ashok Agarwal, who presented his findings at the conference, said they did not prove mobile phones were damaging male fertility, but he called for more research.

"People use mobile phones without thinking twice what the consequences might be," he said.

"It is just like using a toothbrush, but mobiles could be having a devastating effect on fertility."