Recent study claims no evidence of a link between cellphone use and cancer but results were contradictory, leading in both directions

Recently, the British Medical Journal published a paper evaluating the relationship between mobile phone use and gliomas, a type of a cancer that represents 50% of all primary brain tumors. The researchers found no evidence to support the claim that cell phone use increases the likelihood of being diagnosed with a glioma. Unfortunately this doesn't mean that we know cell phones are safe.

In this case-control study, the researchers interviewed 966 patients who had been diagnosed with a glioma in the UK. These patients were asked to recall the frequency and duration of their calls, the side of their head that the phone was used on, whether or not they used hands-free ear pieces, as well as the specific types of phones that were used. The researchers then obtained the same information from 1,716 individuals who did not have cancer. When the two groups were compared, no evidence was found to suggest that there was an increased risk of glioma compared to the cumulative number of calls and hours of use.

The researchers did however encounter interesting findings. There was evidence suggesting that there was a higher risk of developing a tumor on the same side of the brain where the phone was used. Their 95% confidence interval was 1.02 to 1.52, meaning that there was somewhere between 2 to 52% increase in risk for developing a tumor and that there was only a 5% chance that the difference could be less than 2% or higher than 52%. In parallel to this finding, they found a reduced risk of tumor when the phone was used on the opposite side of the head. This time, the range was a 7 to 39% reduction in risk with only a 5% chance that the reduction in risk was less than 7% or greater than 39%.

Despite their conclusion about having no evidence, this bit of data actually supports the claim that cell phones can be dangerous. However, the researchers write that these differences are due to recall bias because patients know the side of their brain that has cancer. Patients may be biased into reporting that they used the cell phone more frequently on the cancerous side.

This inadequate evidence for either conclusion captures the problem of a case-control study: recall bias. If you cannot trust your subjects to accurately remember which side of their heads they use their phones on more frequently, how can you trust the rest of the data? Other problems with the study were that the researchers were only able to interview 51% of the patients who they identified as having gliomas "mainly because rapid death prevented [the researchers] from approaching all of them." Finally, the researchers only looked at one type of brain tumor and not others.

In the end, the study does not give any definitive results. It simply says that evidence could not be found on whether or not cellphones were dangerous. In addition, there was statistical evidence suggesting that tumors were more likely to be seen on the same side a phone was used, although there are confounding variables that may come into play.

While a cohort study (where people are followed over time) would be better than the case-control study (where people are asked to look back in time), the nature of medical research involves doing lower-budget research first before moving on. These types of studies open the door for more expensive and bigger studies. Bottom line? More research is needed before we really know the answer.

More information on gliomas can be found here.

Original article: Hepworth SJ, et. al.  Mobile phone use and risk of glioma in adults: case-control study. BMJ, doi:10.1136/bmj.38720.687975.55 (published 20 January 2006)

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