The question of whether or not there is a link between the use of mobile phones (also called cell phones) and the risk of brain tumors has been cropping up more and more frequently in the media – every time a new study or analysis comes out. This is a very important question of public health as cell phone use is becoming more common, and brain tumors are a very serious and often life-threatening category of diseases.

Of course such questions are best answered by a dispassionate, careful, and systematic look at the science – what is the plausibility of a link and what is the evidence that there actually is one. At this point we are somewhere in the middle of studying this problem. We already have substantial data, but it is conflicting and the research community is still debating on how to get more definitive data everyone can agree upon. So at present there is a variety of opinions on the matter. The consensus seems to be that cell phones probably do not cause brain tumors, but we’re not sure, there is meaningful dissent from this opinion, and so more study is needed.

There are two types of scientific studies we can do to answer this question. The first is biological and looks at the effects of radiation, and specifically the type and strength of radiation emitted by cell phones, on cells in a test tube and on animals. This will tell us if a risk from cell phones is plausible, if there is a mechanism, and what, if any, the effects are likely to be. But this kind of data will not tell us if cell phones in fact have caused or are causing brain tumors.

The second kind of scientific evidence is epidemiological, which looks for a correlation between cell phone use and brain tumors. Epidemiological studies look more directly at the actual question, but have their own complexities and limitations. It is difficult to impossible to perfectly isolate the variable of interest (cell phone use) and measure its correlation to another variable (brain tumors). Further, as soon as you start asking the question a miriad of sub-questions emerge:

How much cell phone use is necessary to cause a brain tumor? This further breaks down to the variable of intensity of the radiation, frequency and duration of exposure, and duration of total exposure, and the delay from exposure to tumor appearance. And further, is there an apparent dose-response – does a higher does of cell phone radiation cause an increased risk of tumors?

What kind of tumors are we talking about? Does use correlate with an increased risk of benign tumors, all tumors, only malignant tumors? Does is correlate with tumors on the side of preferred cell phone use, or anywhere in the brain? What if cell phone use increases the risk of getting cancer from other causes, but is not a risk by itself. In other words, maybe smokers get more smoking-related cancers if they also use cell phones.

Then there is the issue of sub-populations. Are children more at risk? What about men vs women, or those with compromised immune systems?

There are also different ways to look at the data. We can begin with a population of cell phone users and another population of non-cell phone users, follow them over time and keep track of who gets what kind of brain and other tumors. (This is called a cohort study). Or, we can look at 100 people with brain tumors and then quiz them about their prior cell phone use. Or you can do a population study by surveying a large population for a number of variables, like cell phone use and brain tumors, and then do a statistical analysis to look for correlations.

And here we begin to see the problem with epidemiological studies. They provide very useful information, but variables can multiply endlessly forever muddying the waters. A pattern can emerge, however, after multiple different types of epidemiological studies are completed on different populations with varying methods. A consistent pattern favoring a lack of correlation, or a positive correlation, can emerge and become highly reliable. Although it must be pointed out that such studies cannot prove, by definition, the absence of any correlation. They can only set statistical limits on the probable maximum size of any such correlation. A correlation smaller than the power of the studies to detect is always possible.

So what does the current evidence say about cell phone use? The biological studies have largely been negative, although some studies have shown changes in cells or their genes after prolonged exposure to cell phone radiation. However, the exposures were greater than what would occur with even frequent cell phone use, so the utility of these studies are questionable.

The epidemiological evidence can best be described as “mixed.” In other words, there is no strong signal, no strong correlation between cell phones and brain tumors. Neither, however, has any correlation been adequately ruled out. We are still in that pesky “we need more data” phase. Here is the FDA summary of the evidence so far.

A recent meta-analysis suggested that there may be a small increase in risk for certain kinds of tumors only in those with exposure for greater than 10 years. I do not put a great deal of faith in meta-analyses. They have their own problems. I prefer systematic reviews. But sometimes they give a snap shot of the current literature on a specific question.

This meta-analysis also, however, was published before an even more recent, and very large, UK study that found no association between cell phones and tumors. That’s reassuring, but the literature is likely to go back and forth like this for a while. Eventually, all of the criticisms and short comings of prior studies will be used to design a few very large and fairly definitive studies, and then a firmer consensus will likely emerge.

Recently a Neurosurgeon by the name of Dr. Vini Khurana has published on the web the results of his systematic review of the literature (often misleadingly referred to by the press as a new “study”). He concludes that the evidence is trending toward the conclusion that there is a correlation between cell phone use and brain tumors, but only for exposure durations of >10 years. He dismissed much of the negative evidence because they studied primarily exposure durations less than 10 years. His analysis has yet to be peer-reviewed (by report this is in process).

For now, we remain hopeful but cautious. For those who want to err on the side of caution, there are some reasonable recommendations (these come from multiple organizations, so they seem to represent a consensus).

– Limit your cell phone use

– Do not allow small children to begin using cell phones.

– Use a head set to increase the distance from the antenna to your head.

Why not allow kids to use cell phones? This is purely speculative at this point, but the fear is that their thinner skulls will allow more radiation to pass through, their smaller brains will not dissipate the heat as well, and their immature development stage will make them more susceptible to any biological effects. All plausible, but unproven. Studies specifically looking at kids are on the way, but no data yet.

Of course, like any scientific or health issues these days, there is a layer of pseudoscience piled on top of this question. There is one notable crank, Arthur Firstenberg, who has been ranting for years about the evils of cell phones and other wireless technology. His writing reads like classic conspiracy-based fear mongering, with a distinct aftertaste of crank. He quotes numerous dubious scientific claims about cell phones without ever providing proper references, but of course because big industry is hiding what they have all known for nearly a century. Bottom line – don’t believe the hysteria.

There is also a cottage industry of entrepreneurs who would love to sell you a device that protects you from the cell phone radiation. These devices tend to fall into one of three categories: 1) pure magic, like crystals; 2) sound technologically but have no effect; or 3) they actually shield cell phone radiation, but at the expense of the wireless signal that makes them work. So far no one has figured out a way to shield against cell phone radiation without shielding against cell phone radiation.

But just because there are some fear-mongering or greedy pseudoscientists out there does not mean that the claims can be dismissed. What the evidence shows is that there is biological plausibility for a negative effect; the epidemiological evidence for any correlation with <10 years of exposure is mixed but leaning negative, and for >10 years of exposure is mixed but leaning positive. I think we can rule out a strong correlation (meaning a large risk), but not a small one. It is reasonable to caution about cell phone use in kids until we get some data either way. And we need more data all around before the question can be put to bed.

Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the president and co-founder of the New England Skeptical Society, the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also contributes every Sunday to The Rogues Gallery, the official blog of the SGU.