Thursday February 24 2011
Researchers don't know the clinical significance of the results
“Mobile phones are a brain cell killer,” reported The Sun. The newspaper claimed that a study of hundreds of mobile users found that the signals emitted during calls can cause a 7% rise in chemical changes in the brain. It said that these may boost the chances of developing cancer. Other papers also reported the study in a more balanced way.
The laboratory-based study recruited 47 healthy volunteers who had their brain activity measured while they had mobile phones fixed to both sides of their head. One of the handsets received a call on silent for 50 minutes. Brain scans showed there was a 7% increase in brain activity in the area closest to that phone’s antenna.
The Sun over-interpreted the findings of this study and put an alarming spin on it that is not supported by the findings. The study did not show that mobile phones kill brain cells or cause cancer. The size of the effect was small, and the researchers themselves say that the findings are of “unknown clinical significance”. They state that it is not possible to tell from their findings whether or not these effects are harmful. Further research is needed.
Where did the story come from?
The study was carried out by researchers from the National Institute on Drug Abuse, National Institute on Alcohol Abuse and Alcoholism, both in Bethesda, USA, and the Brookhaven National Laboratory in New York. It was supported by the National Institutes of Health and had infrastructure support from the Department of Energy. The study was published in the peer-reviewed Journal of the American Medical Association.
Many papers reported this study, most confirming that there was no suggestion of a health risk. The Daily Mail mentioned that scientists were unsure why mobile phones may increase brain activity, and that the findings do not in any way indicate that they cause cancer. The Sun’s alarming headline – “Mobile phones are a brain cell ‘killer’,” – does not reflect the findings of the study.
What kind of research was this?
This experimental research was conducted in healthy volunteers, who were artificially exposed to low levels of electromagnetic radiation from mobile phones and given a brain scan.
The researchers were interested to see if mobile phone exposure affected brain glucose metabolism, a marker of brain activity.
They say that mobile phone use is now widespread, prompting research into the radiofrequency-modulated electromagnetic fields they emit, the extent to which these penetrate into the brain and whether they are harmful. They say that there is particular concern as to whether these emissions could cause cancer. This has been studied in observational studies with inconclusive results, and the issue remains unresolved.
In randomised crossover studies, such as this one, each volunteer receives a number of interventions in a random order, so that all volunteers get each intervention. This is an appropriate way of testing the short-term physiological effects of phone use.
What did the research involve?
The researchers recruited 47 healthy participants using adverts placed in local newspapers in 2009, in which they were offered $250 to take part. Anyone with medical, psychiatric or neurological diseases was excluded. The researchers made particular efforts to exclude anyone who had recently taken psychoactive drugs (including alcohol and nicotine) as these can affect brain activity. To check for these, urine samples were taken from the participants before each experimental session took place. There were equal numbers of male and female participants, with an average age of 31 years. Most favoured their right ear when using the phone and only 19% favoured their left ear.
A Samsung mobile phone was placed on each of the participants’ ears and secured to their head. The position of the phones’ antennae was adjusted so that the effect of exposure to this part of the phone could be assessed. Each participant was prepared for the brain scan with an injection of fluorodeoxyglucose (18FDG). This commonly used radioactive chemical is used in scans to highlight high-glucose-using cells, such as active brain cells.
The phone of the right hand side of the participant’s head was then called, and a recorded message played for 50 minutes. Both the phones were muted (turned to silent) so the participant could not hear the message and in theory would not know that one of the phones was connected. The electromagnetic emissions around the phones were monitored to check that the phones were working and where the field was strongest. The volunteers were then scanned using positron emission tomography (PET), a device that produces pictures of the brain in which coloured areas show increased glucose metabolism (and, therefore, increased brain activity).
Two scans were taken on two different days. On one of the days, both phones were turned off and didn’t receive calls. On the other day, the right phone was turned on and the left phone was switched off. The participants did not know when or which of the phones was turned on and this was randomly assigned (i.e. the participants were blinded).
Standard statistical testing was used to map and compare the metabolism between the “on” and “off” conditions.
What were the basic results?
Measurements of glucose metabolism across the whole of the brain did not differ whether the phones were turned on or off (metabolism was 41.2 μmol/100 g per minute when the phone was off and 41.7 μmol/100 g per minute when the phone was on and receiving a call).
However, when the researchers looked at particular regions of the brain, they found significant effects in areas close to the phone’s antenna (including the right orbitofrontal cortex and the lower part of the right superior temporal gyrus). Here, the study found a difference in glucose metabolism when the phone was on and receiving a call compared to when it was not. Glucose metabolism was measured as 35.7 μmol/100 g per minute when a phone was active compared with 33.3 μmol/100 g per minute when it was not, a mean difference in glucose metabolism of 2.4 μmol/100 g per minute (95% confidence interval 0.67 to 4.2).
How did the researchers interpret the results?
The researchers say that in healthy participants, 50 minutes of mobile phone exposure was “associated with increased brain glucose metabolism in the region closest to the antenna”. They say that this finding “is of unknown clinical significance”.
This experiment appears to have been carefully conducted. The study found a small significant difference in glucose metabolism in the area of the brain near the antenna of an active mobile phone. There are several points to note about the results that may affect their interpretation, some of which the researchers mention:
- The increase in glucose metabolism is proportionately small (2.4/33.3 μmol/100 g per minute or 7% as the papers quote). Any increased activity in the brain cells due to thinking, for example, could have led to this difference, and the wide confidence interval suggests that the difference in metabolism could have been as low as 0.67/33.3 μmol/100 g per minute or 2%.
- The study does not investigate whether mobile phones cause cancer or, as the researchers say, whether this small increase in brain activity has any detrimental effect.
- It is possible that the participants could tell if the phone was on or off or receiving a call even if they were set to silent. For example, the phone that was turned on may have been warmer. This was not tested or reported by the researchers. This is important because knowing whether the phone was making a call could have influenced the underlying brain activity.
Overall, this study provides useful additional information about the effects of phone use in experimental conditions. The effect observed was small and the researchers clearly state that they do not know the clinical significance of their findings. Further research is needed to clarify if this effect is real, and if so whether increasing the activity of brain cells in this way leads to any long-term harmful effects.