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I can't speak for you, but lots my friends go into a tizzy when groups like the WHO classify cell phones as "possibly carcinogenic". Should you panic? Cell phones and cancer are the topic of this week's Healthcare Triage.

For those of you who want to read more, go here:

John Green -- Executive Producer
Stan Muller -- Director, Producer
Aaron Carroll -- Writer
Mark Olsen -- Graphics
I can't speak for you but lots of my friends go into a tizzy when groups like the World Health Organization classify cell phones as possibly carcinogenic. Should you panic? Cell phones and cancer are the topic of this week's Healthcare Triage.

*theme music*

Let's start by making sure that you all understand that the WHO statement doesn't mean that there's a clear link. It's more akin to saying that there could be some risk and that more research is needed. Putting cell phones in this category means they've now joined the ranks of pickled vegetables and coffee as possibly carcinogenic.

So no, I wouldn't panic yet. But what should you make of all this? Let's start with some facts. Cell phones are hugely popular. Worldwide estimates put cell phone usage at more than three billion users. In the United States, more than 270 million people use cell phones including about half of children age 8-12. And yes, phones do emit radiation, specifically in the 800-2,000 megahertz range. So it's not a surprise that there's an ongoing debate as to whether the widespread use of a device that emits radiation causes cancer.

But the radiation from cell phones is non-ionizing. That puts it in the camp of things like radar, and microwave ovens, and radio waves. This is different than ionizing radiation like that of x-rays, radon, and cosmic rays. Those things lead to DNA changes and cause cancer. There's no evidence that non-ionizing radiation does.

By the way, Wi-Fi and Bluetooth are also forms of non-ionizing radiation. There's no evidence for their causing cancer either. Many, many studies have been published in this area. The vast majority of them are what we call case control studies. Let's review how those work.

For a case control study in this domain, you'd gather a group of people with brain tumors. Then you'd gather a group of people without brain tumors. Then you'd ask them all various questions like "do you use a cell phone?" to see if there are differences between the two groups. While a retrospective case control study like this can be an important study design, it's essential to recognize that they are among the weaker types of studies you can do. Unlike randomized control trials, you can't prove causation with this type of study. Unlike in prospective cohort studies, there's a real problem with what's known as recall bias. This is a type of bias that can alter your results because people with an issue, like a brain tumor, are more likely to recall things that might have caused their brain tumors than those who don't have that same problem. So the danger with case control studies is that people with brain tumors may have heard about this theory that cell phones cause cancer and therefore may remember that they used a cell phone more than people who don't have brain tumors.

So let's try and summarize what we know. To the research!  *music* In 2008 a scientist summarized data in a systematic review of 33 studies in the peer-reviewed literature that looked at cell phones and brain tumors. A surprising number of these studies come from one group in Sweden. The reviewer found major flaws in the research that would make it difficult to draw a convincing conclusion about cell phones and brain tumors. The next year, another group published a meta-analysis of the literature in the Journal of Clinical Oncology. They felt that 23 articles were good enough to be included in the review. All of them were case control studies. They found, overall, that compared to rarely or never using a cell phone, regularly using a cell phone was not significantly related to the development of malignant and benign brain tumors. Even the most recent large study in the review known as the Interphone study found that, and I quote, "cell phone users have no increased risk for two of the most common types of brain tumor-glioma and meningioma".  

The plural of anecdote is not data. As human beings, we make decisions every day that trade off benefits with harms. As we've discussed before, pretty much the biggest killer of children in the United States is car accidents. Yet, no one thinks we should ban cars in order to reduce that to zero. We as a society accept that the quality of life derived from driving outweighs the increase in deaths of children from car accidents. If you disagree, don't drive. Almost no one makes that choice. Similarly, cell phones provide a lot of good to many of people. Given the controversy, even if there was an association between cell phones and brain tumors it would have to be really small. If such a very, very small association exists, few would likely forgo their cell phone to eliminate it completely. Just like they won't forgo their cars.

Moreover, we know that at a population level, there's been no explosion of brain tumors recently. A study published in the Journal of the National Cancer Institute in 2009 examined data for cancers in four countries with registries from 1974 through 2003. Over that time, almost 60,000 people in a population of 16 million adults between 10 and 79 years were diagnosed with brain tumors. While a slow increase in the rates of gliomas and meningiomas was seen throughout the time period, no changes in incident trends were seen from 1998 to 2003 when you'd expect to see an increase because of cell phone use after 5-10 years.

Case control studies are necessary for rare diseases. But cell phone use is so common that if they were dangerous right now, we'd be able to see the effect easily. That's not happening. Future work will be needed to see if they cause long-term harm but as for now, there's very little evidence that they do.