Although children today have never known a world without cell phones, the rest of us remember when these devices were created and have watched their popularity soar. The ability to have constant communication, anytime and anywhere, is now taken for granted. Many have asked the question, are we putting our health at risk with this technology? Specifically, with cell phones cradled against our ears many times a day, and sometimes for many hours a day, are we at increased risk for developing brain tumors? This has been a difficult question for the scientific community to answer. There are many factors that make this answer to this question elusive. To begin with, cell phone use has only become common since the 1990s. Given the latency period required for the development of cancer, it is possible that cell phones still have not been used long enough to show a detrimental effect. However, there is an ever-growing body of literature investigating the potential harms of cell phones and cordless phones.
The basic theory behind why mobile and cordless phones may be dangerous is that they operate by receiving and transmitting radio frequency (RF) waves . Mobile phones either use analog or digital transmission, with analog phones using a higher power to transmit the same amount of data. Transmission of data generates an electromagnetic field, containing electromagnetic radiation. The RF waves of cell phones are in the microwave frequency range. They are not of high enough energy to ionize biological tissue (such as X-rays or gamma rays), so presumably any adverse effects would come from actual heating of the nearby tissue. The amount of energy absorbed by the human head varies according to type of phone, mode of transmission, and patterns of phone use .
Animal models seem like a logical place to look for effects of RF radiation on tissue. An epidemiological review from a group in India from 2008 nicely summarizes the results of several animal studies evaluating the relationship between RF radiation of similar frequency as used in mobile and cordless phone and cancer of several types (brain, lymphoma, breast, skin) . The bottom line is that animal models have not been able to consistently demonstrate that RF radiation initiates or accelerated carcinogenesis. Studies in humans have tended to be retrospective case-control studies. While these have methodological drawbacks and there are many studies finding no increased risk, many studies present some concerning trends.
A 2009 publication in the International Journal of Oncology by a Swedish group gave the results of two retrospective case-control studies between 1997 and 2003, attempting to evaluate for an association between astrocytomas and acoustic neuromas and the use of cellular and cordless phones . 905 patients who had developed tumors, either malignant or benign, were surveyed about whether they used mobile or cordless phones, and on which side of their head they tended to hold the phone. The study found an increased risk of cancer to be associated with holding the phone regularly on that side. Based on their analysis, the strongest correlation was between the development of astrocytomas (grades I-IV) and mobile and cordless phone use in patients with greater than 10 years of telephone use prior to diagnosis. Patients were more likely to have held their phones predominantly on the same side as their tumor, with an OR=5.0, 95% CI=2.3-11.The risk was highest for individuals who had their first use of a cellular or mobile phone under the age of 20. For acoustic neuroma, the study also found an increased risk of ipsilateral mobile and cordless phone use, OR=3.0, 95% CI=1.4-6.2 and OR=2.3, 95% CI=0.6-8.8 respectively. The paper concludes that there is an association between mobile and cordless phone use, acknowledging the limitations of small sample sizes (particularly for acoustic neuromas).
This result supported previous findings from the same author from a meta-analysis from 2007, in which they found an association between acoutic neuromas and gliomas and ipsilateral phone use . A more recent 2009 meta-analysis from the neurosurgical literature from Pittsburg looks at three case-control studies focusing exclusively on the association between cell phone use for at least 10 years and acoustic neuroma development . This analysis found a 2.4-fold greater risk of ipsilateral acoutic neuromas in cell phone users. However, the authors are quick to point out the limitations of retrospective studies to find a true association, as well concerns about recall bias and other confounding factors. Overall, even if studies of this nature suggest a concerning pattern, one is left with many doubts. Recall bias and confounding factors cannot be underestimated.
An epidemiologist in Austria writes about the difficulties of identifying a relationship between cell phones and cancer . In addition to cell phones perhaps not having been around for long enough, there is no evidence-based exposure metric to determine how much exposure would be sufficient to increase risk. That is, how much is too much? Similarly, we are in the dark about the mechanism by which cell phones would directly promote malignancy, and specifically for which types of cancer would the risk be most increased.
Despite the ambiguity in the literature, both by the FDA and by the telecommunications industry have issued clear consensus statements on the matter. As reported by a NYT article in September 2009 , the CTIA, or International Association for the Wireless Telecommunications Industry, assures consumers that there is no conclusive evidence that cell phone use is associated with cancer. The conflict of interest goes without saying. The FDA asserts that “the weight of scientific evidence has not linked cell phones with any health problems” . That said, the FDA also suggests tips to reduce risk – just in case there is some. Headsets and speaker mode can put distance between the phone and the body. Or, something nobody wants to hear, we can simply spend less time on our phones.
Next time on Clinical Correlations: incidence of repetitive strain injury from text messaging?
Dr. Crittenden is a 3rd year internal medicine resident at NYU Medical Center.
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