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A man uses his cellphone in this 2013 file photo.Fernando Morales/The Globe and Mail

A major new study has found that radiofrequency radiation exposure from cellphones appears to cause an increased risk of certain types of cancer in rats.

The highly anticipated study, performed by the U.S. National Toxicology Program and released late Thursday, is one of the more ambitious studies done in an attempt to determine what, if any, health risks cellphones pose.

But the findings, which are already igniting a huge response on social media, are not the final word on this subject. Many more studies need to be performed to fully understand the potential risks of radiofrequency radiation and answer questions about length of exposure and how people can protect themselves.

Here's what you need to know

Researchers with the National Toxicology Program, part of the U.S. Department of Health and Human Services, exposed rats to radiofrequency radiation throughout their lives. They exposed rats to two different radio systems: global system for mobiles (GSM) and code division multiple access (CDMA). In those two groups, rats were further divided so that they could be exposed to varying levels of radiofrequency radiation.

The researchers decided to only look at the effects on two types of tumours: gliomas, which occur in the brain and schwannomas, which form in the tissues that surround nerves.

Brain tumour risks

At the end of the study period, researchers found a "low incidence" of malignant brain tumours in all male rats exposed to GSM radiofrequency radiation. In each group, 2 to 3 per cent of rats developed brain tumours. A small number of male rats in that group also experienced abnormal growth of glial cells, which are found in the brain and central nervous system.

In the CDMA group, brain tumours were only found in the male rats exposed to the highest level of radiofrequency radiation. About 3 per cent of the rats in that group developed brain tumours. Four rats – two in the lowest exposure group and two in the highest – had abnormal glial cell growth.

None of the male rats in the control group developed brain tumours or had abnormal cell growth.

Among female rats, there was only one brain tumour identified in a rat exposed to the highest levels of radiofrequency radiation in the GSM group and two in the group exposed to the lowest amount of radiofrequency radiation in the CDMA group. One female rat in the GSM group had abnormal glial cell growth, compared to one rat in each of the exposure categories of the CDMA group.

None of the females in the control group developed brain tumours or had abnormal cell growth.

Heart tumour risks

The researchers also studied cardiac schwannomas in male rats in all of the groups exposed to radiofrequency radiation. Groups exposed to the highest amount of radiofrequency radiation had larger numbers of schwannomas. For instance, two male rats in the GSM group exposed to the lowest radiofrequency radiation developed heart schwannomas compared to five in the group exposed to the highest amount. A small number of male rats also had abnormal Schwann cell growth.

There were no cardiac schwannomas found in the control group.

Once again, the female rats didn't appear to be as greatly affected. In total, six female rats exposed to radiofrequency radiation had heart schwannomas. One female rat in each of the CDMA groups had abnormal Schwann cell growth.

None of the female controls had schwannomas or abnormal Schwann cell growth.

What this means

It's important to keep in mind that researchers only looked at two types of tumours. And that results in rats don't necessarily translate to humans. But the findings represent a significant contribution to this rapidly evolving field of study. The experts who worked on this study have additional research they will be publishing next year.

While the number of tumours found in rats exposed to radiofrequency radiation is not overwhelming, the study authors note that "even a very small increase in the incidence of disease resulting from exposure … could have broad implications for public health."

What not to do: panic

We already knew that radiofrequency radiation from cellphones could be linked to cancer. The World Health Organization's International Agency for Research on Cancer has already classified the electromagnetic fields produced by cellphones as possibly carcinogenic.

That doesn't mean using a cell phone is a guarantee you will get cancer, as some headlines suggest. It means there are potential risks for certain types of cancer depending on the frequency of level of exposure. The questions that need to be answered are what exactly those risks are, how they are impacted frequency of exposure, age and other factors, and how to mitigate the potential health problems.

In the meantime, Anthony Miller, professor emeritus in the division of epidemiology at the University of Toronto's Dalla Lana School of Public Health, said Health Canada should review its position on the risks of radiofrequency radiation. Health Canada says on its website the "vast majority of scientific research to date does not support a link" between radiofrequency exposure and cancer. Miller said this new study, along with the IARC's classification, should prompt the federal government into action to better inform Canadians about the concerns.

"I think they need to know there is a risk," he said.

The flaws

The study has several shortcomings that need to be kept in mind, said Dr. Jim Woodgett, director of research and a senior investigator at Toronto's Lunenfeld-Tanenbaum Research Institute. For one thing, the control group of rats, overall, died sooner than the rats exposed to radiofrequency radiation. So the rats in the exposure group weren't dying from the cancer they developed. Woodgett also noted that cancer is relatively common in aging animals. If the control group had lived as long as the exposure group, several of them may have developed cancer, he said.

It's also difficult to translate results in a rat population to human health risks, said Dr. Paul Demers, director of the Occupational Cancer Research Centre.

"Trying to basically extend these results to humans is always tricky," Demers said.

The study itself was also not very large. There were 90 rats in each group, which may sound like a lot, but isn't when you are trying to arrive at very reliable conclusions, Woodgett said.

Overall, the risks from cellphones are likely very small, he said. The average person faces a much greater risk from dying if they text and drive while using a cellphone, Woodgett added.

Regardless, people need to be cautious when interpreting these results, Demers said.

"This is still an open question," he said.

How to reduce your exposure

As researchers try to better understand this issue, the World Health Organization and other experts note there are things people can do to reduce their exposure. Radiofrequency exposure is highest the closer you are to your phone, so keep it away from your body by using a headset or speakerphone to make calls. The WHO also advises limiting the number and duration of calls and using your phone in areas with good reception, which enables cell phones to use less power.

"Distance is your friend," said Miller.

And while there are a growing number of devices on the market promising to reduce radiofrequency exposure, they have "not been shown to be effective," the WHO says.

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