mythbuster graphic Besides being a hazard to safe driving, cell phones have been accused of causing brain tumors. Where does this concern come from?

Cellular (cell) phones use radiowaves to carry information between callers. The frequency of these waves ranges from about 850-1900 megahertz (MHz), which is somewhere between the frequencies used by FM radio stations and microwave ovens. The higher the frequencies, the greater the energy carried by the waves.

While waves of higher energies can heat living tissues enough to cause damage, the heat generated by cell phones is so small that few scientists believe they can do any damage to human users.

Nonetheless, some types of brain tumors have been increasingly diagnosed since the cell phone era began (most notably, acoustic neuroma, which can affect hearing). Still, no studies have conclusively proven a causal relationship between cell phone use and the development of brain tumors. But don’t hang up on the myth just yet–this one doesn’t have an easy answer.

Numerous large studies have failed to show a clear connection between cell phone use and overall risk of developing brain cancer.

One study conducted in Sweden compared 233 brain cancer patients diagnosed between 1994-1996 with 466 controls (people who did not have brain cancer). Another study conducted by the American Health Foundation compared 469 brain cancer patients diagnosed between 1994-1998 in New York, Massachusetts, and Rhode Island with 422 controls. And a third study conducted by the US National Cancer Institute compared 782 brain cancer patients diagnosed in Arizona, Pennsylvania, and Massachusetts between 1994-1998 with 799 controls.

All of these studies found that patients with brain cancer did not report using cell phones more than those in the control group. These findings were consistent, regardless of what type of brain cancer was present or where in the brain the tumor was located. Ironically, some of the findings indicated a lower risk of brain tumors among cell phone users, reasons for which were not determined. It may have been only a statistical anomaly.

Also, most of the studies did not find a link between the side of the head on which the brain tumors occurred and the side of the head on which the cell phone was used. While the findings of the Swedish study were not conclusive on this point, researchers have pointed out that because the patients in the study knew which side their brain tumors were on, it may have biased the accuracy of their reported cell phone use.

Two other more recent studies have had similar results. A study conducted in England from 2000-2004 looked at 966 people diagnosed with brain glioma (a type of brain tumor) and 1716 controls. Researchers did not find evidence that cell phone usage increases the risk of the brain tumors studied. It also found no association with risk of brain tumors based on duration of use, side of use, or amount of cell phone use.

These results were similar to those of a Danish study published in the April 12, 2005 issue of Neurology, the scientific journal of the American Academy of Neurology. This study of 427 people with brain tumors and 822 people without, again demonstrated no increased risk of brain tumors with cell phone use, frequency of use, or number of years of use. The Danish study was somewhat unusual in that in addition to questioning participants about their cell phone habits, it also obtained records from their cell phone companies to document some of the participants’ phone usage, thus increasing the accuracy of the study.

Despite this added reassurance, the study’s author pointed out that because a relatively small portion of the Danish population has used cell phones regularly for more than ten years, longer studies are needed to conclusively determine the long-term effects of cell phone use in this group.

Most of the studies conducted on the subject have found no evidence that using digital cell phones increases a user’s risk of developing any type of brain tumor. But some studies have found that brain tumor patients who use cell phones have tumors that grow faster than tumors in those who don’t use cell phones.

A Swedish study conducted between 1997-2000 among 1429 patients with brain tumors and 1470 controls yielded somewhat mixed results. While the use of cordless phones and digital cell phones did not suggest any increase in the cancer rate, the study did find that users of analog cell phones had a slightly greater risk of developing brain tumors than did nonusers of cell phones, and the risk increased for each year of use.

Analog cell phones operate on a different frequency than digital cell phones. They have become less popular since digital cell phones were introduced. They use a different type of battery, and use a continuous electronic signal, in contrast with the intermittent “pulse” signal used by digital cell phones.

Also, the study found that while there was no increase in the number of tumors among digital cell phone users, among those users who had brain tumors, some of the tumors tended to grow more quickly, suggesting that the frequencies used by digital cell phones may encourage tumor growth, but do not necessarily cause tumors to develop.

A recent study published in the British Journal of Cancer by Japanese investigators concluded that there was no increased overall risk of glioma or meningioma among the mobile phones users as related exposure to radiofrequency electromagnetic field. This study used a novel approach that took into account the different exposure levels inside the intracranial space.

Although the research to date has been largely reassuring, some scientists aren’t yet ready to dismiss the possibility that cell phone use—especially for prolonged periods of time—may influence risk of brain tumors. This is because the most reliable method of uncovering a real connection between cell phone use and brain tumors would be to follow a group of healthy volunteers who use cell phones at different rates over a long period of time. If brain tumors occurred more commonly in frequent users compared to infrequent users, a link would be likely. The trouble with this approach is that brain tumors are extremely rare events, so research would require following many subjects over many years to obtain meaningful results. Cell phones haven’t been around nearly long enough to make such a study likely.

Despite numerous studies, there is no convincing evidence that digital cell phone use causes brain tumors. However, some studies suggest that cell phone use may increase the rate of tumor growth in patients with certain types of brain tumors that already existed. Also, some of the earliest studies of large groups of cell phone users found that analog cell phones may have slightly increased the risk of developing brain tumors.

Although few people today use analog cell phone technology, and digital cell phones appear to be safe for the vast majority of users, there is no way to know the long-term health consequences of frequent cell phone use. Let’s face it, though. This small, lingering risk is highly unlikely to inhibit most members of a society that has become obsessed with its ability to communicate with everyone, all the time.