This is a science and medicine story we have been following for a while – out of personal and scientific interest, and the need to correct confused or misleading new reporting on the topic. Are cell phones linked to an increased risk of brain cancer or other tumors? New data is reassuring.
David Gorski and I have both written on this topic. To give a quick summary, there is no convincing data to link cell phone use and brain cancer. Epidemiological studies have not found an increase in the incidence of brain cancer following the widespread adoption of cell phones in the mid 1990s – as one would expect if there were a causal relationship. Further, large scale studies have not found any consistent correlation between cell phone use and brain cancer.
It is clear from the literature that there is no measurable increased risk from short term cell phone use – less than 10 years. There is no evidence to conclude that there is a risk from long term use (> 10 years) but we do not yet have sufficient long-term data to rule out a small risk. Further, the data is somewhat ambiguous when it comes to children – still no convincing evidence of a link, but we cannot confidently rule out a link.
Further, the plausibility of a connection is quite low. While electromagnetic radiation from cell phones is a physical mechanism that can potentially have an effect, it is generally too weak to have any plausible biological effect. This by itself is very reassuring, but still cannot rule out a possible effect from cell phones through some as yet undiscovered biological effect of cell phone radiation.
So the claim for a link between cell phones and brain cancer has low plausibility, good epidemiological evidence for a lack of association for less than 10 years of exposure in adults, and equivocal but generally negative evidence for children and greater than 10 years of exposure in adults. Longer term studies will hopefully address these latter issues more definitively.
With that as background, we have the newly published results of the Interphone study. This is an epidemiological study involving 13 different countries looking for any correlation between cell phone use and two common types of brain tumors – glioma and meningioma. Parts of this data have been previously published, but this is now the first time data from all 13 participants has been published – including “2,708 people with glioma, 2,409 with meningioma and 7,658 matched controls.”
The overall findings of the study were negative – no clear association between cell phone use and gliomas or meningiomas. However, there were two interesting subgroup findings. For those with regular use of cell phones there was a 20% decrease in risk of tumors compared to those without any use of cell phones.
As implausible as it is that cell phones cause brain cancer, it is even more implausible that they protect against cancer. So, it’s possible this is just noise in the data. However, epidemiologist Anthony Swerdlow, who was involved in the UK arm of the study, gives another explanation:
“We have evidence that the people who refused to be controls are people who didn’t use phones. This meant that the control group, consisting of people without cancer, was rather skewed, appearing to have more mobile-phone use than would be found in a representative sample from the general population. “The controls were over-represented with phone users.”
These results, therefore, were very likely due to a systematic bias in the data – such are the perils of epidemiology.
The other correlation found was a 40% increase in risk of brain tumor among the top 10% of mobile phone users. This is an interesting result, because it suggests a dose response effect. However, this result is also questionable and may be due to methodology. It turns out that many of the people answering the survey used in the study reported improbable amounts of cell phone use – such as 12 hours per day. It was therefore considered to be an unreliable method of determining cell phone use. Number of calls made per day gave more realistic results, and therefore may be easier for people to understand or remember. When the data is viewed with number of calls made instead of time per day, the correlation with brain tumors disappears.
So at the end of all this, we are pretty much where we started. There is still no evidence to link cell phone use and cancer. This data has a few quirks in it, but in the final analysis is probably negative. So we can be a bit more confident in the lack of correlation – or we can think of it as shrinking a bit further the upper limit of any possible effect from cell phone use.
The study does extend the duration of our data somewhat as well – to about 15 years. But we still lack long term data for exposure greater than 15 years.
Unfortunately, the wrinkles in this study lead to some confusion among the media. While reporting this study it is possible to emphasize the increased risk among the highest cell phone users, while either missing or glossing over the fact that further analysis shows this correlation is probably not real. For example, Science News reports: “Interphone study finds hints of brain cancer risk in heavy cell-phone users.” Many other outlets repeated the headline that the study was “inconclusive.”
Cell phones are an increasingly common tool of modern society. It is certainly necessary and valid to carefully study their safety and monitor for possible adverse health outcomes from their regular use. I am reassured by the current evidence, however, that there is no large risk from cell phones. There is either no risk or a very small long term risk.
Consider, however, that you are probably at greater risk of premature death from using your cell phone while driving, or from driving at all. So as individuals we always need to balance a small risk against the convenience of new technology. The better data we have and the better we understand that data – the better we will be able to make informed decisions for ourselves.