Wednesday, April 7, 1999 Published at 18:01 GMT 19:01 UK
Jury still out on mobile health
Research on mobile phones is difficult to interpret
The jury is still out on whether mobile phones harm users' health, according to an investigation by the New Scientist.
The report comes as new research is expected to show improved reaction times for people who use mobile phones.
A study by the University of Bristol, to be published in the International Journal of Radiation Biology on Thursday, suggests mobile phone users have reaction times which are around 4% faster than non-users.
Alan Preece, who led the research, speculates that it could be that the microwaves from the phones speed up the flow of electrical signals through a part of the brain which connects areas related to vision and language.
But he does not know why they might do this and what the long-term effects might be.
David Concar of the New Scientist says other studies of mobile phones have come up with similar surprising results.
Research by the University of Nottingham found that nematode worms exposed to microwaves grew 5% faster than normal.
This suggested that microwaves increased cell division, leading to fears of links between mobile phones and cancer.
However, David de Pomerai, who led the research, says there is no reason to panic.
"Exposing a nematode worm to microwaves overnight is like exposing a human continuously for an entire decade," he stated.
The team are trying to figure out what causes the changes.
They believe they may be related to stress.
Henry Lai at the University of Washington found that rats exposed to microwaves showed signs of stress.
For example, they produced natural painkillers called endorphins.
Other research suggests that microwaves may impair the electrical activity of rat's brains and weaken their reactions.
But David Concar says the implications are not clear because the research, by John Tattersall at the Defence Evaluation and Research Agency, only looked at microwaves' effect on cells from deep within the brain.
Mobile phones would be unlikely to affect brain cells at such a level, says Mr Concar.
Other studies have suggested mobile phones could increase the risk of cancer.
But all have been difficult to substantiate. For example, an Australian study of mice which suggested microwaves from the phones increased the likelihood of developing lymphoma.
But the results have been impossible to reproduce.
Meanwhile, a US study found that mice exposed to microwaves for two hours a day were less likely to develop brain tumours when they were fed a cancer-causing chemical.
Mr Concar says the discrepancy between studies suggests that any cancerous effect mobile phones may have is likely to be tiny.
However, he adds that it is still too early to know whether the phones can cause changes to brain activity and memory.
The World Health Organisation is finalising plans for the biggest ever study of mobile phones and their health effects.
The $6m study, which is partly funded by mobile phone firms, will compare the mobile phone use of around 3,000 Europeans with brain tumours with a control group without tumours.
However, there are concerns that the study's results will be difficult to interpret, for example, because brain tumours can take years to develop.
The New Scientist has also investigated whether devices for shielding people from microwaves are effective.
It found that performance depended on the type of phone.
Hands-free mobiles were the least likely to cause radiation problems.
Meanwhile, researchers at the University of Surrey are developing a smart antenna which directs microwaves away from the head.