no real evidence that cell phones used by 97 million Americans cause health hazards beyond car crashes
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Cell phone study finds no cancer link
But findings unlikely to end the debate
The Denmark study did not look into whether cell phones are linked to other conditions such as migraine headaches or skin diseases.
MSNBC NEWS SERVICES
Feb. 6 Scientists who tracked the health of 420,000 Danish cell phone users found no sign the devices increase cancer risk. But the reassuring findings aren’t likely to end the controversy.
‘Every which way we looked at it, we could not find any suggestive evidence for elevated risks.’
JOHN BOICE study co-author
THE STUDY, published in this week’s Journal of the National Cancer Institute, concluded cell phone users are no more likely than anyone else to suffer brain or nervous system cancers, leukemia or salivary gland tumors, cancer types that have worried critics.
"Every which way we looked at it, we could not find any suggestive evidence for elevated risks," said John Boice of the International Epidemiology Institute in Rockville, Md., who co-authored the study with Christoffer Johansen of Copenhagen’s Danish Cancer Society.
But the study did not clear cell phones of other health risks, Johansen said.
"We have only addressed the cancer question," he said. "We cannot exclude that long exposure to mobile phones can cause ringing noises in the head, migraine, headaches and other symptoms of the central nervous system.
He said it was theoretically possible that diseases like Parkinson’s and Alzheimer’s, various types of dementia and nervous complaints might be associated with mobile phones, as well as skin diseases at points where the device comes into contact with users.
DEBATE NOT OVER
Taken together with two recent, smaller U.S. studies that found no cancer risk, the research should "minimize the concern and fears that the public has with regard to the use of these phones," Boice said.
But it won’t end the debate. Several thousand Danes had used their phones for more than 10 years, the time it can take a slow-growing brain tumor to appear, but the majority had used them for only about three years.
Consequently, "this study ... should not be taken as the final answer," said University of Washington professor Henry Lai, whose laboratory research linked cell phone signals with damage to rat brain cells.
"It’s reassuring ... but not enough that it closes the book on this question," added Boston University epidemiology professor Kenneth Rothman.
Federal health officials insist there’s no real evidence that cell phones used by 97 million Americans cause health hazards beyond car crashes caused by people yakking while driving.
Yet no health or government agency gives the popular gadgets a definitively clean bill of health, either. Unable to give a clear answer, the Food and Drug Administration tells worried consumers they can simply use an earphone device that keeps the phone’s antenna away from the head.
Concern about mobile phones stems from the fact that when used, they emit low levels of radio-frequency energy or radiation, scientists say. Some experts studying potential links between cell phone use and cancer have noted that it takes ionizing radiation - the kind put out by microwave ovens and radioactive materials - to make the changes in cells associated with cancer. Cell phones do not produce this type of radiation.
Most research - including two recent U.S. studies that examined 2,400 people, some who had used cell phones for five years - has found no risk.
But a few small studies have raised concern. They include Lai’s rat data and a Swedish study that found brain tumors more likely on the side of the head on which cell phones were used.
With more than 82 million Americans using cell phones, there's been growing interest in further studies to try to determine, once and for all, if cell phones pose health risks. The Food & Drug Administration prepared this backgrounder to help explain what's known, and what's left to be researched.
Why the concern?
Mobile phones emit low levels of radiofrequency energy (i.e., radiofrequency radiation) in the microwave range while being used. They also emit very low levels of radiofrequency energy (RF), considered non-significant, when in the stand-by mode.
It is well known that high levels of RF can produce biological damage through heating effects (this is how your microwave oven is able to cook food). However, it is not known whether, to what extent, or through what mechanism, lower levels of RF might cause adverse health effects as well.
Although some research has been done to address these questions, no clear picture of the biological effects of this type of radiation has emerged to date. Thus, the available science does not allow us to conclude that mobile phones are absolutely safe, or that they are unsafe. However, the available scientific evidence does not demonstrate any adverse health effects associated with the use of mobile phones.
What kinds of phones are in question?
Questions have been raised about hand-held mobile phones, the kind that have a built-in antenna that is positioned close to the user's head during normal telephone conversation.
These types of mobile phones are of concern because of the short distance between the phone's antenna -- the primary source of the RF -- and the person's head. The exposure to RF from mobile phones in which the antenna is located at greater distances from the user (on the outside of a car, for example) is drastically lower than that from hand-held phones, because a person's RF exposure decreases rapidly with distance from the source.
The safety of so-called "cordless phones," which have a base unit connected to the telephone wiring in a house and which operate at far lower power levels and frequencies, has not been questioned.
How much evidence is there that hand-held mobile phones might be harmful?
There is not enough evidence to know for sure, either way. The existing scientific evidence is conflicting and many of the studies that have been done to date have suffered from flaws in their research methods.
Animal experiments investigating the effects of RF exposures characteristic of mobile phones have yielded conflicting results. A few animal studies, however, have suggested that low levels of RF could accelerate the development of cancer in laboratory animals.
In one study, mice genetically altered to be predisposed to developing one type of cancer developed more than twice as many such cancers when they were exposed to RF energy compared to controls.
There is much uncertainty among scientists about whether results obtained from animal studies apply to the use of mobile phones. First, it is uncertain how to apply the results obtained in rats and mice to humans. Second, many of the studies that showed increased tumor development used animals that had already been treated with cancer-causing chemicals, and other studies exposed the animals to the RF virtually continuously--up to 22 hours per day.
What is known about cases of human cancer that have been reported in cell phone users?
Some people who have used mobile phones have been diagnosed with brain cancer. But it is important to understand that this type of cancer also occurs among people who have not used mobile phones.
In fact, brain cancer occurs in the U.S. population at a rate of about 6 new cases per 100,000 people each year. At that rate, assuming 80 million users of mobile phones (a number increasing at a rate of about 1 million per month), about 4,800 cases of brain cancer would be expected each year among those 80 million people, whether or not they used their phones. Thus it is not possible to tell whether any individual's cancer arose because of the phone, or whether it would have happened anyway.
A key question is whether the risk of getting a particular form of cancer is greater among people who use mobile phones than among the rest of the population.
One way to answer that question is to compare the usage of mobile phones among people with brain cancer with the use of mobile phones among appropriately matched people without brain cancer. This is called a case-control study. The current case-control study of brain cancers by the National Cancer Institute, as well as the follow-up research to be sponsored by industry, will begin to generate this type of information.
In the absence of conclusive information, what can concerned individuals do?
If there is a risk from these products -- and at this point we do not know that there is -- it is probably very small. But if people are concerned about avoiding even potential risks, there are simple steps they can take to do so.
For example, time is a key factor in how much exposure a person receives. Those persons who spend long periods of time on their hand-held mobile phones could consider holding lengthy conversations on conventional phones and reserving the hand-held models for shorter conversations or for situations when other types of phones are not available.
People who must conduct extended conversations in their cars every day could switch to a type of mobile phone that places more distance between their bodies and the source of the RF, since the exposure level drops off dramatically with distance. For example, they could switch to
A mobile phone in which the antenna is located outside the vehicle.
A hand-held phone with a built-in antenna connected to a different antenna mounted on the outside of the car or built into a separate package.
A headset with a remote antenna to a mobile phone carried at the waist.
STUDY DETAILS
Denmark provides a strong look at the issue thanks to the unique Danish Cancer Registry that tracks every citizen who gets cancer, using personal identification numbers assigned to each Dane at birth.
"Our study is the first nationwide, population-based analysis of its kind. It is important because the link-up of information from different administrative systems could simply not be done in other countries," Johansen said.
Johansen used cell phone company records to identify Danes who began using the phones between 1982 and 1995. Using those personal ID numbers, he matched phone users with the registry’s cancer records through the end of 1996, to determine of cell callers suffered cancer at the same rate as other Danes.
Based on national cancer rates, 161 of the cell phone users should have suffered brain or nervous system cancer, and 154 of them did. Similarly, there were 84 leukemia cases instead of an expected 86, and seven salivary gland tumors instead of the expected nine.
Phone use didn’t affect which side of the brain a tumor was on, nor did the study find any increase in very rare tumors, called neuropitheliomas and acoustic neuromas, that some studies have linked to cell phones.
The study couldn’t track how long all 420,000 Danish callers actually spent on the phone. But Boice said people who began using the phones about three years ago were spending 30 to 60 minutes a day talking, and that duration of use showed no risk.
The "beautifully designed" study and "rock-solid database make it difficult to take issue with the report’s conclusion," Robert Park of the American Physical Society wrote in an accompanying editorial.
The Associated Press and Reuters contributed to this report
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