MEN who regularly carry a mobile phone could have their sperm count reduced by as much as 30 per cent.
Those who place their phone near their groin, on a belt or in a pocket, are at greatest risk, new research has revealed.
The findings, to be presented at an international conference this week, are the first to suggest male fertility could be affected by the radiation emitted by mobile phones, also long suspected of causing cancer.
The study by Hungarian researchers found the sperm that did survive exposure to mobile phone radiation showed abnormal movements, further reducing fertility.
But Australian experts advised men not to panic yet.
Monash IVF's medical director Gab Kovacs said a man's sperm count "goes up and down quite a bit" and could vary greatly from one day to the next.
"You'd expect a 30 per cent variation just among men randomly," he said.
He said the test finding would need to be repeated in further research before they could be seen as conclusive.
"I wouldn't throw out my mobile phone at the moment," Professor Kovacs said.
David de Kretser, director of Andrology Australia and the Monash Institute of Reproduction and Development, said it was difficult to verify the research, as it was unclear how much radiation the men had been exposed to.
The research will be presented tomorrow at the European Society of Human Reproduction and Embryology's annual conference in Berlin.
Researchers from the University of Szeged studied 221 men for 13 months and compared the sperm of those who used their mobile phones heavily with those who did not.
Researcher Imre Fejes of the University's obstetrics and gynaecology department wrote: "The prolonged use of cell phones may have a negative effect on spermatogenesis (sperm production) and male fertility, that deteriorates both concentration and motility."
Dr Fejes said further work was needed to confirm the finding and discover how it happens.
Unlike previous studies, the researchers believe mobile phones may cause damage while in stand-by mode, when mobiles are not in use but still make regular transmission to maintain contact with radio towers.
It had been assumed such transmissions were too short to cause harm.
By Helen Tobler
The Sunday Times