The largest study yet performed by a peer review board of public scientific research indicates that there is "no clear evidence" that cell phone radiation is harmful to public health. This report, which was just published by the Health Protection Agency's independent advisory group on non-ionising radiation (AGNIR), was a collection of other reports and scientific studies accumulated since 2003. The review board said it was "important" to watch for signs of rising cancer cases, which included monitoring national brain tumor trends. According to their findings so far, there is "no indication" of increased risk.

They did indicate that there have been subtle and tiny changes detected in low frequency brain waves with cell phone usage, but, at this time, it's unclear if they had any effect, and overall the no-harm evidence is more overwhelming now. Here's a quote with some more details,"There are still limitations to the published research that preclude a definitive judgement, but the evidence overall has not demonstrated any adverse effects on human health from exposure to radiofrequency fields below internationally accepted guideline levels," said Professor Anthony Swerdlow, chairman of AGNIR and an epidemiologist at the Institute of Cancer Research."

And, here's a quote with a final summation,

In making recommendations for future research, the report emphasised a need to focus on new and emerging devices that emit radiofrequency radiation, and to gather more data on cancer risk among those who have used phones for more than 15 years.

"There is no convincing evidence that radiofrequency exposure causes health effects in adults or in children but beyond 15 years for mobile phones, we have to say we have little or no information," Swerdlow said. "I think it is important therefore, to some extent, to keep an eye out on this, which we will do into the future."

"Remember this is an exposure that 20 years ago nobody had and now practically everybody has so you might expect that if there were appreciable effects that you would see them in the tumour rates," he said. "But if this is something that takes 15, 20 years or more to show up we have no reason to think there is an effect if it takes a long time to show up, we need to keep watching the rates just in case."

Professor Patricia McKinney at the centre for epidemiology and biostatistics at Leeds University said: "The general public should be reassured by the conclusions on mobile phone use as the current evidence does not support any causal link to brain tumours or other cancers. However, the conclusions relate to mobile phone exposures of up to 15 years and further monitoring of possible risks is needed."
Source: The Guardian