Mobiles do not cause tumours, scientists find

One of the most comprehensive studies into the dangers of mobile phones has found no link between how often they are used and the risk of developing brain tumours.

One of the most comprehensive studies into the dangers of mobile phones has found no link between how often they are used and the risk of developing brain tumours.

But scientists said that although they could not establish a link between the two, they could not rule out the possibility that mobile handsets may cause long-term health problems, and even head cancers.

Researchers questioned more than 1,200 people, of whom 822 were healthy and 427 had brain tumours. When they compared the two groups, they found the risk of developing a brain tumour was not related to the frequency of mobile phone calls or the number of years they had been used.

Christoffer Johansen, of the Danish Cancer Society in Copenhagen, said the research findings supported earlier studies that found no links between brain tumours and mobile phones.

"I think we're becoming more convinced the use of mobile phones does not pose a risk in terms of brain cancer," Professor Johansen said.

"In terms of brain tumours, the door is now more closed than it was on the question but, before we can turn the key in the lock, we need to study a high number of long-term, heavy users of mobile phones."

The Danish study looked at the two main types of brain tumour - glioma and meningioma - and found that neither was related to mobile phone use.

They also found that there was no association between the side of the head habitually used by a mobile phone user and on which side of the brain a tumour developed.

By checking the mobile phone bills of 27 people with brain tumours and 47 people without tumours, the researchers were also able to assess how good the each person's memory was in terms of how they recalled using their phones.

They found that people accurately remembered the number of calls they made but did not accurately remember the length of those calls.

The scientists also checked to see whether patients with tumours were more likely to exaggerate their mobile phone habits than healthy patients - they were not. "We've no reason to believe that the people who took part in the study were not reporting their phone use faithfully," Professor Johansen said.

Several laboratory studies have suggested that the radiation emanating from mobile phones could damage living tissues and one in particular demonstrated that a long conversation on a mobile phone can cause small temperature rises in the brain.

Most large-scale epidemiological studies have however failed to find a link between ill health and excessive mobile phone use. Nevertheless, some have found a statistically significant association, Professor Johansen said.

"There have been a few studies that found an increased risk of brain tumours with phone use but those studies have been criticised for problems with the study design," he said.

"Taken together, the weight of evidence does not indicate that cellular telephones are a risk factor of glioma or meningioma of the brain. Nevertheless, in all the studies the numbers of long-term users and heavy users are limited, obviating any firm conclusion.

"In our study, few persons reported regular cellular telephone use for 10 years or more. We won't be able to make any firm conclusions on this issue until we can confirm these results with studies with more long-term and heavy cell-phone users," Professor Johansen said.

An official inquiry into the health risks of mobile phones in Britain has recommended children under eight should not be allowed to use phones and older children between eight and 14 should only use them when absolutely necessary.

Professor Johansen said the latest study published in the journal Neurology was the most comprehensive and detailed so far but it did not include children so the findings were only applicable to adults.

He said the next phase of the research was scheduled to be an investigation into the small number of children with brain tumours to see if they could be linked with the use of mobile phones.

Previous studies are inconclusive

Test-tube studies have indicated the radiofrequency fields emitted by mobile phones could, in certain circumstances, damage living cells.

Long conversations on a mobile phone have been shown to heat the brain, which could, in theory, cause headaches or more severe long-term damage.

However, most scientists believe the radiation from mobile phone headsets is too weak to break or damage the chemical bonds of DNA in living tissue and so cause cancer.

Most large-scale studies on the human population - including three in the US and one in Denmark - have also failed to establish an association.

However, a Finnish study of 398 people with brain cancer did find a significantly increased risk among users of the older analogue headsets, which tended to have higher power outputs than the newer, digital phones.

Two further studies in Sweden produced mixed results. One involving 588 cases did not find a statistical link while the second, involving 1,617 cases, did find a significant association with brain tumours on the side of the head on which the telephone was normally held - regardless of whether the handset was analogue or digital. But those studies have been heavily criticised for introducing potential bias in terms of the questions that were asked when the patients were interviewed and the method used to choose the patients .

Sir William Stewart, the head of the Health Protection Agency, said the scientific evidence was still too weak to say that mobile phones were safe. He said the public should follow a precautionary approach especially when it came to children, who were likely to suffer most if there was a risk to health.

Steve Connor