July 23, 2018

Do cellphones cause cancer? What the research tells us (and doesn't)

Daily Briefing

    Despite many years of research into the health effects of cellphone radiation, a Vox review of existing research suggests there is still no definitive answer to whether cellphones might cause cancer in some circumstances—and many experts believe it might not be possible to fully understand cellphone radiation's effects on human health, Vox reports.

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    There are two main types of radiation: ionizing and "non-ionizing" radiation.

    Ionizing radiation—which we are exposed to during X-rays, CT scans, and air travel—has been proven to cause cellular and DNA damage with prolonged exposure.

    "Non-ionizing" radiation, on the other hand, is commonly viewed as harmless because it does not contain enough energy to damage DNA by ionizing, or removing electrons from, atoms and molecules. This type of radiation is emitted by computers, microwaves, and remote controls—and it includes the radio-frequency radiation emitted by cellphones and wireless network towers. 

    While researchers generally believe cellphones and other types of non-ionizing radio-frequency radiation exposure are harmless, some experts and consumer advocacy groups have raised concerns about the devices' possible links to cancer and infertility. Om Gandhi, a radiation expert at the University of Utah, for instance, argued, "These electromagnetic waves may cause effects on cellular functions but not damage the cells per se."

    But to date, there has been limited quality research on the matter—and some experts say we are unlikely to ever have a large reliable study examining the issue.

    Barriers to understanding health effects of cellphones

    Experts say a key barrier to understanding and evaluating the effects of cellphone radiation is the dearth of data from randomized controlled studies.

    The majority of human studies into the health effects of cellphones are observational, such as systematic reviews or cohort studies, Vox reports. According to Vox, observational studies "only tell us about associations between phenomena, not whether one thing caused another to happen." Further, Vox reports some of the research has been funded by the cellphone industry, which increases the risk for bias.

    Even so, plenty of existing research has attempted to tease out the role of cellphone radiation. Vox's Julia Belluz and clinical epidemiologist Dylan Collins conducted a systemic review to identify and analyze the highest-quality research available.

    Research shows mixed findings on cancer incidence and tumors

    For the analysis, Belluz and Collins scoured 49 studies on cellphones and human health published over the past decade that explored cancers and benign tumors around the head and neck.

    They identified 12 systematic reviews. Using an evaluation tool called AMSTAR, they found that 8 of those reviews were of "critically low" quality, which meant they did not provide accurate research summaries. The remaining four reviews ranked "low" or "moderate" on quality, but Vox reports the studies "relied mainly on case-control studies—a very weak type of observational study design when it comes to proving causality."

    Belluz and Collins found those case-control studies suggest cellphone use may not pose a cancer risk, with a few limited exceptions seen in blinded studies or those that examined long-term cellphone use. In those cases, researchers observed potential associations between cellphone use and an increased risk of cancer—but noted that the quality of the studies are too low to be conclusive.

    Belluz and Collins also reviewed five recent cohort studies, which Belluz writes have "a stronger type of study design" than case-control studies. Overall, they found the research showed no increased risk for cancer but a small increased risk in noncancerous tumors.

    Quinn Ostrom, a Baylor College of Medicine researcher who has examined cancer trends, said, "We see either no change or very small increases in incidence in some tumor types. I would be inclined to say this isn't as much of an increase as you might expect if cellphones were causative [of brain tumors] due to the very sharp way use of these devices has gone up over the last 20 years."

    Is high-quality, human research achievable?

    However, several researchers note that none of the existing studies on cellphone radiation in humans have been randomized controlled trials, which typically are considered the "gold standard" for scientific evidence, Vox reports—and some experts believe such a trial is not achievable.

    That is because it would require researchers to randomly assign cellphone use levels to thousands of study participants—including a control group that would be barred from using cellphones—and have study participants commit to those usage levels for at least five years, Vox reports.

    Several researchers also argue that the way people use cellphones and the available wireless networks changes too frequently to study. Belluz writes, "Unfortunately, even the best evidence on cellphones and brain tumors is far from ideal. Remember, these cohort studies are still observational research—not experimental studies like randomized controlled trials. That means they can't tell us about causation, and there are still many ways they could be biased."

    As such, some experts have turned to animal-based studies to better understand the potential effects of cellphone radiation on human health, Vox reports.

    For example, NIH's National Toxicology Program in February released draft research on the effects of high exposure to radio frequency radiation on mice and rats. After being exposed to high radio frequency radiation, rats developed brain tumors in more frequently, but mice did not, the researchers found.

    John Bucher, a senior scientist at the National Institute of Environmental Health Sciences and a co-author of the NIH research, said, "[Our results] go against the notion that non-ionizing radiation is completely harmless," which, according to Vox, means the radiation cellphones emit could at least cause animals to experience biological changes, such as promoting tumors. 

    Are cellphones safe?

    Overall, the Vox analysis found industry-funded and non-industry-funded research "all seem to point in the same direction: Using these devices is not associated with an increased risk of brain tumors in humans—though there are many open questions about their health effects."

    Jonathan Samet—dean of the Colorado School of Public Health, who advised the World Health Organization on cellphone radiation and cancer—said one could form an argument in either direction based on the available evidence, "because there's not enough evidence to start with."

    In the meantime, Vox reports, people who are concerned about their exposure to radio frequency radiation can keep their "cellphone off [their] body, wear wired earpieces when [they] use it to reduce your exposure to radiation, and [not] sleep with your cellphone next to your pillow" (Belluz, Vox, 7/16).

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