About 30 studies have looked at possible links between cell phone use and tumors. Most of these studies have focused on brain tumors. Many of these have been case-control studies, in which patients with brain tumors (cases) were compared to people free of brain tumors (controls), in terms of their past use of cell phones.
In general, these studies have yielded similar results:
• In most studies patients with brain tumors do not report more cell phone use overall than the controls. This finding is true when all brain tumors are considered as a group, or when specific types of tumors are considered.
• Most studies do not show a “dose-response relationship” — a tendency for the risk of brain tumors to increase with increasing cell phone use, which would be expected if cell phone use caused brain tumors.
• Several studies published by the same research group in Sweden report increased risk of tumors on the side of the head where the cell phone was held, particularly with 10 or more years of use. It is hard to know what to make of these findings because studies by other researchers have not had the same results, and there is no overall increase in brain cancer in Sweden during the years that correspond to these reports.
The 13-country INTERPHONE study, the largest case-control study done to date, looked at cell phone use among more than 5,000 people who developed brain tumors (gliomas or meningiomas) and a similar group of people without tumors. Overall, the study found no link between brain tumor risk and the frequency of calls, longer call time, or cell phone use for 10 or more years. There was a suggestion of a possible increased risk of glioma, and a smaller suggestion of an increased risk of meningioma, in the 10% of people who used their cell phones the most. But this finding was difficult to interpret because of some people reporting implausibly high cell phone use, as well as other issues. The researchers noted that the shortcomings of the study prevented them from drawing any firm conclusions, and that more research was needed.
A large, long-term study following more than 420,000 cell phone users in Denmark between 1982 and 2002 had findings similar to those of the case-control studies. Cell phone use, even for more than 10 years, was not linked with an increased risk of brain tumors, salivary gland tumors, or cancer overall, nor was there a link with any brain tumor subtypes or with tumors in any location within the brain. This type of study (following a large group of people going forward in time and not relying on people’s memories about cell phone use) is generally thought to be stronger than a case-control study. But there are still limits as to how well this study might apply to people using cell phones today. For example, while the cell phones used at the time of the study tended to require more power than modern cell phones, people also probably used the phones less than they do today.
In summary, most studies published so far have not found a link between cell phone use and the development of tumors. However, these studies have had some important limitations that make them unlikely to end the controversy about whether cell phone use affects cancer risk.
First, studies have not yet been able to follow people for very long periods of time. When tumors form after a known cancer-causing exposure, it usually takes decades for them to develop. Because cell phones have been in widespread use for less than 20 years in most countries, it is not possible to rule out future health effects that have not yet appeared.
Second, cell phone usage has been and is constantly changing. People are using cell phones much more than they were even 10 years ago, and the phones themselves are very different from what was used in the past. This makes it hard to know if the results of studies looking at cell phone use in years past would still apply today.
Third, the studies published so far have focused on adults, rather than children. Cell phone use is now widespread even among young children. It is possible that if there are health effects, they might be more pronounced in children because their nervous systems are still developing and their lifetime exposure will be greater than adults, who started at a later age.
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