New study raises questions about cell phone safety

Rat study offers support for World Health Organization conclusion that heavy cell phone use may cause cancer
Aug 4, 2016 — 7:00 am EST
girl on phone

People love cell phones, which is why nine in 10 Americans own one. Many use them hours a day. So even a small cancer risk from their use — which has just been suggested by an animal study — could have important health implications.


Does heavy use of cell phones pose a risk of cancer? This question has provoked controversy for many years. A new study in rats now adds to those concerns. Its data linked long-term, intense exposure to radiation from cell phones with an increased risk of cancer in the heart or brain.

The results have yet to be confirmed, the authors note. Moreover, they add, it’s not yet clear what the findings may mean in terms of human health.

Indeed, although the rat study found a link between cell-phone radiation and cancer, it offers no clues to why such a link might exist, notes Jonathan Samet. He teaches preventative medicine and directs the Institute for Global Health at the University of Southern California in Los Angeles. Still, he calls the new study’s findings “significant.” They could lead to studies probing how cell-phone radiation might cause cancer, he says.

Phone signals are relayed between cell towers and cell phones via radio waves. This radiofrequency — or RF — radiation is a type known as non-ionizing. Unlike X-rays and alpha particles, non-ionizing radiation does not deposit enough energy into cells to release electrons from atoms or molecules, producing ions. So it tends to be far less harmful than ionizing radiation, such as X-rays. But that does not mean radio waves might not cause harm.

In very large doses this radiation will heat the body and cause tissue damage. But it’s not yet known what much lower RF levels might do, such as those from cell-phone use. Five years ago, the World Health Organization’s International Agency for Research on Cancer, or IARC, concluded that cell-phone use “is possibly carcinogenic.” That means it might cause cancer.

Its conclusion was based on what little research data were available at that time. But notice that IARC was not certain. It said only that phone use might “possibly” cause cancer. So scientists at the National Toxicology Program, or NTP, decided to investigate further.

Newfound risks are small, but perplexing

NTP is part of the National Institute of Environmental Health Sciences. It’s in Research Triangle Park, N.C. Scientists at NTP study risks posed to people by things in the environment, such as radiation (X-rays, for instance) and chemicals (including bug killers, solvents and fire retardants).

Its new study found a small increase in cancer risk from cell-phone radiation. The scientists had exposed rats and mice to the same types of radiation emitted by U.S. cell phones. The findings that they released on May 26 come from rats. (NTP’s mouse data should emerge within the next 18 months.) The cancers in these rats resembled those seen in some human studies that had probed harm from cell phone use. For this reason, NTP says that its findings appear to support IARC’s conclusion that heavy cell-phone use might be harmful.

little girl with phone
More than half of U.S. kids age 8 to 12 have or use a cell phone.
Andrey Popov/iStockphoto

Still, “much work remains to be done to understand implications of these findings,” says John Bucher. He’s associate director of NTP. “The results are far from definitive,” he says. By that he means they could change, as more data come in.

The new findings do, however, raise important questions that warrant further study, says Bucher. For instance, he notes that the brain tumors that emerged in the rats are not a common type. Yet they are the type seen in some studies of human cell-phone users. They even occurred in the same part of the brain as did those that showed up in people.

NTP decided, last month, to share its early findings because cell phone use has become a basic feature of modern life. Nine out of 10 Americans own a cell phone. Nearly eight out of every 10 U.S. teens have or use a cell phone, as do more than half of all kids age 8 to 12 years old. So even a very small increase in harm from cell phone use could pose some threat to most people, NTP argues.

A big, complex study

NTP’s new cell-phone probe involved more than 7,000 animals. (That includes the work with mice, which will be reported next year.) This research took two years and cost $25 million. “These have been some of the most technically challenging studies we’ve ever attempted,” Bucher says.  

cage racks
Inside a radio-wave radiation test chamber are two racks containing cages. This is where the rats lived while they were being exposed.

The studies exposed animals to two types of radio waves. Each type is used in one of the two major radio systems that broadcast cell-phone signals. One system is known as the CDMA (for Code Division Multiple Access). In the United States, it’s used by many cell-phone networks, including Sprint and Verizon. The other is known as GSM (for Global System for Mobile communications). GSM radio frequencies are used throughout much of the world. They include some U.S. carriers, too, such as AT&T and T-Mobile. NTP used both RF types to see if their effects might differ.

The researchers exposed groups of 90 female rats and 90 male rats to three different levels of RF radiation. For more than 9 hours each day, the RF signals cycled on and off. They would be on for 10 minutes, then off for 10 minutes. Then the cycle repeated.

Exposures started just before a mother rat gave birth. Once her pups were born, their exposures would continue for another two years. Separate groups of 90 male and 90 female rats — known as the controls — were exposed to no radiation at all. In all, the rat study involved 1,260 animals. And by the time the study had ended, each rat was equivalent in age to a 60-year-old human.

The animals’ exposures differed in major ways from what people would experience. First, people do not talk on the phone all day long — from the womb through old age — for 10 out of every 20 minutes. Second, the animals’ whole bodies were exposed to the radio waves, not just their heads. Doses also were higher and more extensive than any human would encounter.  However, none were high enough to heat the rats’ bodies nor to affect their growth.

Roughly 2 to 3 percent of male rats exposed to the RF radiation developed certain types of brain cancers. Rats in the control group developed none. In addition, between 2 and 6.6 percent of the exposed males developed potentially cancerous heart lesions. (Lesions are areas of damaged tissue.) Again, the control animals did not.

But the number of animals used in these tests was not large, notes Michael Lauer. He works  at the National Institutes of Health in Bethesda, Md. This heart doctor is its deputy director for research that NIH funds in labs elsewhere. Says Lauer, the small number of animals used in the RF tests can make it hard to home in on why an unusual number of them developed cancer.

For now, because more of the rats developed heart lesions, the NTP scientists find this apparent risk from cell phones more compelling. A few female animals got cancer, but not more than tends to occur in any large group of rats.  For that reason, the scientists see no measurable cell-phone cancer risk in these rats. 

Curiously, rats in the control group were about twice as likely to have died (from a range of other causes) as were the rats exposed to RF radiation.

What might this mean for people?

Bucher says the new findings don’t necessarily mean that people should use cell phones less. It’s simply too early to know what to make of the new findings, he stresses.

But the U.S. Food and Drug Administration, or FDA, does have guidelines for safe cell-phone use. (FDA had asked NTP to look into health effects of cell phone radiation.) In guidelines issued 18 months ago, FDA said: “If there is a risk from being exposed to [RF] energy from cell phones — and at this point we do not know that there is — it is probably very small.” But, it added, people worried about health risks might choose to reduce their overall RF exposure. Anyone can do that, FDA points out, by using a headset or a phone’s speaker option. That way, the phone isn’t held next to the head.

boy with phone
Kids today are exposed to RF radiation from cell phone much earlier than their parents were. That concerns some scientists, because the lifetime over which today’s youngsters are exposed will be far longer than for their parents.

New data, such as the NTP findings, may now prompt some “tweaks” to FDA’s recommendations, Bucher says. 

Christopher Portier is more cautious about RF risks. He helped launch the new study when he was NTP’s associate director. (He now works for the Environmental Defense Fund, a nonprofit group that focuses on the environment.) Portier is most concerned about children’s use of devices that emit RF radiation.

Most people who are now adults grew up before cell phones were common, he notes. But children now use these phones as much as — or more than — adults. So “Children would be experiencing exposure for a much longer portion of their lifetimes,” he argues. Given that fact, along with new study’s data, “We should look carefully at children’s use of these devices,” he says.

He, too, pointed to advice (such as FDA’s) on how to limit exposure to cell phone radiation. “Distance is your friend,” Portier says. As with any type of radiation, he notes, the dose falls with distance. So, he says, don’t carry the phone on your body. And, he adds, “Keep the phone away from your head as much as possible.”

Big questions remain

If cell phones are dangerous, why aren’t U.S. brain cancer rates increasing? It’s an important question. But one for which there are no answers. It’s also unclear why female rats in the NTP study showed no increased risk of cancer. 

Researchers do not yet know how long it might take for the type of tumors seen in the study’s rats to develop in people. It can take a decade or longer after exposure to some cancer-causing agents before tumors emerge. For now, Bucher notes, “It’s very reassuring that there is no dramatic increase” in brain cancer rates in people. “It may well be that current cell phone use is safe,” he says.

girl using phone with headset
One way to limit any risks that might be linked with cell-phone use, FDA recommends, is to listen with a headset or hands-free option.

That’s the view of the Cellular Telecommunications Industry Association. CTIA represents the companies that make and service mobile phones. It said that many health groups “have determined that the already existing body of peer-reviewed and published studies shows that there are no established health effects” from  cell phones. By peer review, CTIA is referring to studies that have been reviewed and challenged by scientists who were not involved in the research.

"Call phone use has increased dramatically over the last 30 years, from virtually zero to now most people," notes the NIH's Lauer. "And yet," he notes, "we have not seen any marked increase in the rate of brain cancers." But he adds: "Science is incremental," meaning it advances in small steps. So a study like this one must be considered along with others when investigating risks. As a scientist, he argues, it's unwise to conclude that cell phones are dangerous — or are not — based on one limited study.

FDA is now reviewing the new study's findings to decide if its earlier conclusions about cell phone risks should be changed. In a May 27 statement, FDA noted that earlier studies “have not linked cell phones with any health problems.” But for people who are concerned, FDA points to an easy way to cut any risks: Spend less time on the phone.

Power Words

(for more about Power Words, click here)

agent    A compound or activating form of energy (such as light or other types of radiation) that has a role to play in getting something done.

cancer   Any of more than 100 different diseases, each characterized by the rapid, uncontrolled growth of abnormal cells. The development and growth of cancers, also known as malignancies, can lead to tumors, pain and death.

carcinogen    Something that causes cancer.

control   A part of an experiment where there is no change from normal conditions. The control is essential to scientific experiments. It shows that any new effect is likely due only to the part of the test that a researcher has altered. For example, if scientists were testing different types of fertilizer in a garden, they would want one section of it to remain unfertilized, as the control. Its area would show how plants in this garden grow under normal conditions. And that give scientists something against which they can compare their experimental data.

Food and Drug Administration(or FDA)    A part of the U.S. Department of Health and Human Services, FDA is charged with overseeing the safety of many products. For instance, it is responsible for making sure drugs are properly labeled, safe and effective; that cosmetics and food supplements are safe and properly labeled; and that tobacco products are regulated.

frequency   The number of times a specified periodic phenomenon occurs within a specified time interval. (In physics) The number of wavelengths that occurs over a particular interval of time. (in the electromagnetic spectrum) The one or more wavelengths of energy — from gamma rays and visible light through infrared and radio regions of the spectrum.

implication    The meaning or conclusion that can be drawn after considering a group of circumstances or data.

ionizing radiation    Any of various types of energy delivered by photons or particles — and capable of depositing enough of their energy to whatever they might hit to knock off an electron from an atom or molecule. Doing so would create an ion, or electrically charged particle or molecule. Examples of ionizing radiation include X- and gamma-rays, alpha particles, beta particles, neutrons, protons and deuterons.

lesion    A tissue or part of the body that shows damage from injury or disease. Lesions come in all shapes and sizes, both inside the body and on its outside. A pus-filled wound on the skin is one example. Cells with holes in them or missing parts due to disease represent a totally different class of lesions.

nonionizing radiation    A term for electromagnetic energy that travels in waves or particles (photons) but does not deposit enough energy on the things it hits to knock off an electron, creating a charged particle (ion). Examples of nonionizing radiation types include infrared light, visible light, ultraviolet light and radio waves.

peer review   (in science) A process in which scientists in a field carefully read and critique the work of their peers before it is published in a scientific journal. Peer review helps to prevent sloppy science and bad mistakes from being published

pup   A term given to the young of many animals, from dogs and mice to seals.

radiation    (in physics) One of the three major ways that energy is transferred. (The other two are conduction and convection.) In radiation, electromagnetic waves carry energy from one place to another. Unlike conduction and convection, which need material to help transfer the energy, radiation can transfer energy across empty space.      

radiofrequency (or RF)     Electromagnetic wave frequencies that are used for communications or radar signals.

radio waves    Waves in a part of the electromagnetic spectrum; they are a type that people now use for long-distance communication. Longer than the waves of visible light, radio waves are used to transmit radio and television signals; it is also used in radar.

tumor    A mass of cells characterized by atypical and often uncontrolled growth. Benign tumors will not spread; they just grow and cause problems if they press against or tighten around healthy tissue. Malignant tumors will ultimately shed cells that can seed the body with new tumors. Malignant tumors are also known as cancers.

World Health Organization    An agency of the United Nations, established in 1948, to promote health and to control communicable diseases. It is based in Geneva, Switzerland. The United Nations relies on the WHO for providing international leadership on global health matters. This organization also helps shape the research agenda for health issues and sets standards for pollutants and other things that could pose a risk to health. WHO also regularly reviews data to set policies for maintaining health and a healthy environment.

Word find (Click here)


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  • HS-PS4-4

Further Reading

A. Lenhart. “Teens, Social Media & Technology Overview 2015.” Pew Research Center. April 9, 2015.

A. Yeager. “Smartphone users’ thumbs are reshaping their brains.” Science News. December 23, 2014.

L. Sanders. “Cell phone research suggests fetal risk.” Science News. March 19, 2012.

J. Raloff. “Cell phone-cancer study an enigma.” Science News. June 19, 2010.

J. Raloff. “Interphone study finds hints of brain cancer risk in heavy cell-phone users.” Science News blog. May 17, 2010.

J. Raloff. “Cell phones: Precautions recommended.” Science News blog. September 16, 2009.

J. Raloff. “Cell phones: Feds probing health impacts.” Science News blog.  September 14, 2009.

J. Raloff. “Two studies offer some cell-phone cautions.” Science News blog. November 1, 2002.

Cell Phones and Cancer Risk, a website of the U.S. National Cancer Institute that answers some basic questions about the issues.