Radiation from mobile phones may allow toxic chemicals to leak into the brain, a study suggested yesterday.
The research from Finland, although at an early stage, strengthens fears that mobiles could be harmful to health.
A study of rats by a French team is said to support the evidence by indicating that mobile phone radiation can weaken the natural "blood-brain barrier" that protect the brain from poisons.
Results from both investigations are due to be presented at a conference in Canada this month.
The Scandinavian study was led by Professor Darius Leszczynski, of the Radiation and Nuclear Safety Authority in Finland.
Cells from blood vessel walls in the brain were placed in culture dishes and subjected to mobile phone radiation in the laboratory.
At a strength of two watts per kilogram, the radiation intensity was the maximum allowed internationally for mobile phones.
After an hour's exposure biochemical changes were seen in the cells which could alter the activity of about 400 proteins. In particular one enzyme, called HSP 27, which helps to regulate blood-brain barrier permeability, was affected.
"If the same thing happened in real life, in people, then it could affect blood-brain barrier permeability by increasing it," said Professor Leszczynski.
As a result, molecules that cause damage to neurons may be allowed to invade brain tissue.
The professor said it would be wrong to assume at this stage that mobile phones were hazardous to human health. "I would not yet say it is worrying, because we are not rats," he said. "But in my opinion this research does justify putting more money into human studies to find out whether this is a real danger or just the result of us using such sensitive methods."
He added that for the time being he had no qualms about using a mobile phone.
More than 40 million people in Britain have mobile phones, many of them children. Two years ago a government inquiry concluded that they posed no provable health risk.
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