(PhysOrg.com) -- Preliminary results of an International investigation by the World Health Organization (WHO) suggest there may be a "significantly increased risk" of some types of brain tumors after use of mobile phones for a decade or more.

The investigation lasted a decade and covered studies of 12,800 people in 13 countries during the period 2000 to 2004. Six of eight studies on brain tumors found a link between an increased risk of the most common type of brain tumor, glioma, and heavy use of mobile phones, with one finding a 39 percent increase. Of seven studies into a benign tumor of a nerve between the brain and the ear (acoustic neurinoma), two found an elevated risk in people using cell phones for ten years or more.

Previous studies have yielded inconclusive results, but head of the WHO study, Dr Elisabeth Cardis, said the report would include a public health message and a recommendation the use of mobile phones by young children should be restricted. She noted that cell phones can be an important tool in emergencies, and maintaining contact between parents and children can be reassuring, and therefore she would not go as far as suggesting their use should be banned.

Dr Cardis said that a number of studies have suggested possible deleterious effects of the radio frequency radiation emitted by mobile phones, and while these studies were limited and not yet definitive, precautions are important, especially in their use by children except for essential calls.

Critics of the study have pointed out that it included people who only made one call a week using a cell phone, and it did not include any children, both of which could underplay the results. They also point out the research was partly funded by the mobile phone industry. Other critics have noted that some results suggested short-term use appeared to protect against cancer, which may indicate flaws in the studies.

Publication of the results of the 30 million dollar investigation has been delayed because of disagreements over the best way to present the conclusions, but the findings have been submitted and are expected to be published within the next few months.

Meanwhile, for people in the market for a new cell phone who are interested in limiting their exposure to radiation, the Environmental Working Group has published a guide to the radiation emitted by most models of cell phone, as explained in this article.

You can also reduce exposure by sending text rather than speaking, and by avoiding cell phone use if the signal is weak, because the radiation is greatest then. Children should also limit their use because their skulls are thinner and less able to protect their brains from the radiation.

© 2009 PhysOrg.com

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