A study, published in the journal Occupational and Environmental Medicine by Lennart Hardell and colleagues from the University Hospital in Orebro, found no extra risk of brain tumours in people who lived in cities but up to three times greater risk for country dwellers.

One possible explanation, Dr Hardell said, was the adaptive power control systems used in mobile phones to adjust power output. In rural areas, where base stations are further apart, the phones operate at higher power levels. “We found that the risk of brain tumours was higher for people living in rural areas than in towns,” he said.

Use of mobiles has increased rapidly worldwide but the evidence that they do any harm is inconclusive. Some scientists have suggested that the radio frequency fields used by the phones could interfere with biological systems.

Dr Hardell and his colleagues studied 1,429 people with brain tumours and 1,470 people in a healthy control group living in central Sweden. They compared the use of mobile phones of the analogue and digital type, and hands-free phones, between the cases and the people in the control group.Their data enabled risks to be assessed separately for urban and rural areas. They found that rural dwellers who had been using a mobile phone for more than three years were three times more likely to have a brain tumour than city dwellers. After more than five years of use the risk was four times greater. For malignant tumours, the risk was eight times greater but this result was based on so few cases that it cannot be relied upon. No increased risk was found for cordless phones, which operate at a different frequency. The older analogue phones showed little evidence of any increased risk.

“We still cannot exclude that there might be other undetected risks in the countryside, but we have tried to adjust the results, as far as we know,” Dr Hardell said. The study was small and the findings needed to be duplicated, he added. Michael Clark, science spokesman at the Health Protection Agency, said: “The results should be interpreted with caution. Because of uncertainties in our knowledge about this technology, we have recommended a precautionary approach on the use of handsets.

“People, particularly children, should minimise usage until research is properly evaluated over the next few years.”

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