Epidemiologic studies use information from several sources, including questionnaires and data from cell phone service providers, to estimate radiofrequency radiation exposure in groups of people. Direct measurements are not yet possible outside of a laboratory setting. Estimates from studies reported to date take into account the following:.
Researchers have carried out several types of population studies to investigate the possibility of a relationship between cell phone use and the risk of tumors, both malignant cancerous and benign nonmalignant. Epidemiologic studies also called observational studies are research studies in which investigators observe groups of individuals populations and collect information about them but do not try to change anything about the groups.
Two main types of epidemiologic studies— cohort studies and case-control studies —have been used to examine associations between cell phone use and cancer risk. Cohort studies are limited by the fact that they may only be able to look at cell phone subscribers, who are not necessarily the cell phone users. The tumors that have been investigated in epidemiologic studies include malignant brain tumors, such as gliomas , as well as benign tumors, such as acoustic neuroma tumors in the cells of the nerve responsible for hearing that are also known as vestibular schwannomas , meningiomas usually benign tumors in the membranes that cover and protect the brain and spinal cord , parotid gland tumors tumors in the salivary glands , skin cancer, and thyroid gland tumors.
Three large epidemiologic studies have examined the possible association between cell phone use and cancer: Interphone, a case—control study; the Danish Study, a cohort study; and the Million Women Study, another cohort study. These studies have been critically evaluated in reviews reported in 9 and in The findings of these studies are mixed, but overall, they do not show an association between cell phone use and cancer 11 — How the study was done: This is the largest case—control study of cell phone use and the risk of head and neck tumors.
It was conducted by a consortium of researchers from 13 countries. The data came from questionnaires that were completed by study participants in Europe, Israel, Canada, Australia, New Zealand, and Japan. What the study showed: Most published analyses from this study have shown no increases overall in brain or other central nervous system cancers glioma and meningioma related to higher amounts of cell phone use.
One analysis showed a statistically significant , although small, increase in the risk of glioma among study participants who spent the most total time on cell phone calls.
However, for a variety of reasons the researchers considered this finding inconclusive 11 — An analysis of data from all 13 countries reported a statistically significant association between intracranial distribution of tumors within the brain and self-reported location of the phone However, the authors of this study noted that it is not possible to draw firm conclusions about cause and effect based on their findings.
An analysis of data from five Northern European countries showed an increased risk of acoustic neuroma in those who had used a cell phone for 10 or more years In subsequent analyses of Interphone data, investigators investigated whether tumors were more likely to form in areas of the brain with the highest exposure.
One analysis showed no relationship between tumor location and level of radiation However, another found evidence that glioma and, to a lesser extent, meningioma were more likely to develop where exposure was highest How the study was done: This cohort study linked billing information from more than , cell phone subscribers with brain tumor incidence data from the Danish Cancer Registry.
What the study showed: No association was observed between cell phone use and the incidence of glioma, meningioma, or acoustic neuroma, even among people who had been cell phone subscribers for 13 or more years 18 — How the study was done: This prospective cohort study conducted in the United Kingdom used data obtained from questionnaires that were completed by study participants.
What the study showed: Self-reported cell phone use was not associated with an increased risk of glioma, meningioma, or non-central nervous system tumors. Although the original published findings reported an association with an increased risk of acoustic neuroma 21 , this association disappeared after additional years of follow-up of the cohort In addition to these three large studies, other, smaller epidemiologic studies have looked for associations between cell phone use and individual cancers in both adults and children.
These include:. Researchers have carried out several kinds of studies to investigate possible effects of cell phone use on the human body. In , two small studies were published that examined brain glucose metabolism in people after they had used cell phones.
The results were inconsistent. One study showed increased glucose metabolism in the region of the brain close to the antenna compared with tissues on the opposite side of the brain 30 ; the other study 31 found reduced glucose metabolism on the side of the brain where the phone was used.
The authors of these studies noted that the results were preliminary and that possible health outcomes from changes in glucose metabolism in humans were unknown. Such inconsistent findings are not uncommon in experimental studies of the physiological effects of radiofrequency electromagnetic radiation in people Some factors that can contribute to inconsistencies across such studies include assumptions used to estimate doses, failure to consider temperature effects, and investigators not being blinded to exposure status.
Another study investigated blood flow in the brain of people exposed to radiofrequency radiation from cell phones and found no evidence of an effect on blood flow in the brain Early studies involving laboratory animals showed no evidence that radiofrequency radiation increased cancer risk or enhanced the cancer-causing effects of known chemical carcinogens 33 — Because of inconsistent findings from epidemiologic studies in humans and the lack of clear data from previous experimental studies in animals, in the Food and Drug Administration FDA nominated radiofrequency radiation exposure associated with cell phone exposures for study in animal models by the US National Toxicology Program NTP.
This large project was conducted in highly specialized labs. The rodents experienced whole-body exposures of 3, 6, or 9 watts per kilogram of body weight for 5 or 7 days per week for 18 hours per day in cycles of 10 minutes on, 10 minutes off. A research overview of the rodent studies , with links to the peer-review summary, is available on the NTP website.
The primary outcomes observed were a small number of cancers of Schwann cells in the heart and non-cancerous changes hyperplasia in the same tissues for male rats, but not female rats, nor in mice overall.
These experimental findings raise new questions because cancers in the heart are extremely rare in humans. Schwann cells of the heart in rodents are similar to the kind of cells in humans that give rise to acoustic neuromas also known as vestibular schwannomas , which some studies have suggested are increased in people who reported the heaviest use of cell phones.
The NTP plans to continue to study radiofrequency exposure in animal models to provide insights into the biological changes that might explain the outcomes observed in their study.
Another animal study, in which rats were exposed 7 days per week for 19 hours per day to radiofrequency radiation at 0. Among the rats with the highest exposure levels, the researchers noted an increase in heart schwannomas in male rats and nonmalignant Schwann cell growth in the heart in male and female rats.
The gaps in the report from the study raise questions that have not been resolved. ICNIRP an independent nonprofit organization that provides scientific advice and guidance on the health and environmental effects of nonionizing radiation critically evaluated both studies. It concluded that both followed good laboratory practice, including using more animals than earlier research and exposing the animals to radiofrequency radiation throughout their lifetimes. However, it also identified what it considered major weaknesses in how the studies were conducted and statistically analyzed and concluded that these limitations prevent drawing conclusions about the ability of radiofrequency exposures to cause cancer A few studies have shown some evidence of statistical association of cell phone use and brain tumor risks in humans, but most studies have found no association.
Reasons for these discrepancies include the following:. The most consistent health risk associated with cell phone use is distracted driving and vehicle accidents 44 , Several other potential health effects have been reported with cell phone use. Neurologic effects are of particular concern in young persons.
However, studies of memory, learning, and cognitive function have generally produced inconsistent results 46 — In , the International Agency for Research on Cancer IARC , a component of the World Health Organization, appointed an expert working group to review all available evidence on the use of cell phones.
The working group indicated that, although the human studies were susceptible to bias, the findings could not be dismissed as reflecting bias alone, and that a causal interpretation could not be excluded. The working group noted that any interpretation of the evidence should also consider that the observed associations could reflect chance, bias, or confounding variables rather than an underlying causal effect. In addition, the working group stated that the investigation of brain cancer risk associated with cell phone use poses complex research challenges.
The National Institute of Environmental Health Sciences NIEHS states that the weight of the current scientific evidence has not conclusively linked cell phone use with any adverse health problems, but more research is needed.
The US Food and Drug Administration FDA notes that studies reporting biological changes associated with radiofrequency radiation have failed to be replicated and that the majority of human epidemiologic studies have failed to show a relationship between exposure to radiofrequency radiation from cell phones and health problems.
The Federal Communications Commission FCC concludes that currently no scientific evidence establishes a definite link between wireless device use and cancer or other illnesses. In , the European Commission Scientific Committee on Emerging and Newly Identified Health Risks concluded that, overall, the epidemiologic studies on cell phone radiofrequency electromagnetic radiation exposure do not show an increased risk of brain tumors or of other cancers of the head and neck region 9.
The committee also stated that epidemiologic studies do not indicate increased risk for other malignant diseases, including childhood cancer 9. A large prospective cohort study of cell phone use and its possible long-term health effects was launched in Europe in March Participants in COSMOS completed a questionnaire about their health, lifestyle, and current and past cell phone use when they joined the study.
This information will be supplemented with information from health records and cell phone records. The challenge of this ambitious study is to continue following the participants for a range of health effects over many decades. Researchers will need to determine whether participants who leave the study are somehow different from those who remain throughout the follow-up period.
Although recall bias is minimized in studies such as COSMOS that link participants to their cell phone records, such studies face other problems. For example, it is impossible to know who is using the listed cell phone or whether that individual also places calls using other cell phones. To a lesser extent, it is not clear whether multiple users of a single phone, for example family members who may share a device, will be represented on a single phone company account. Additionally, for many long-term cohort studies, participation tends to decline over time.
There are theoretical considerations as to why the possible risk should be investigated separately in children. Their nervous systems are still developing and, therefore, more vulnerable to factors that may cause cancer. Their heads are smaller than those of adults and consequently have a greater proportional exposure to radiation emitted by cell phones.
And, children have the potential of accumulating more years of cell phone exposure than adults. Thus far, the data from studies in children with cancer do not suggest that children are at increased risk of developing cancer from cell phone use. The study included children who were diagnosed with brain tumors between and at the ages of 7 to 19 years. Researchers did not find an association between cell phone use and brain tumor risk by time since initiation of use, by amount of use, or by the location of the tumor Several studies that will provide more information are under way.
Researchers in Spain are conducting another international case—control study, known as Mobi-Kids , which will include 2, young people aged 10—24 years with newly diagnosed brain tumors and 4, healthy young people. FDA is responsible for testing and evaluating electronic product radiation and providing information for the public about the radiofrequency energy emitted by cell phones.
FCC sets limits on the emissions of radiofrequency energy by cell phones and similar wireless products. The dose of the energy that people absorb from any source of radiation is estimated using a measure called the specific absorption rate SAR , which is expressed in watts per kilogram of body weight The SAR decreases very quickly as the distance to the exposure source increases.
For cell phone users who hold their phones next to their head during voice calls, the highest exposure is to the brain, acoustic nerve, salivary gland, and thyroid. SARs for older phones can be found by checking the phone settings or by contacting the manufacturer. FDA has suggested some steps that concerned cell phone users can take to reduce their exposure to radiofrequency radiation 53 :. It is now up to the NTP to either accept or reject the reviewer's conclusions.
A final report is expected within several months. The exposure measures therefore differed from the absorbed doses calculated during the NTP study. The exposures began when the rats were fetuses and continued for 19 hours a day until the animals died from natural causes. As in the NTP study, Ramazzini investigators detected statistically elevated rates of heart schwannomas in male rats at the highest dose.
They also had weaker findings linking RF exposure to cancer of glial cells in the brain, which were limited to females. Just why Schwann and glial cells appear to be targets of cell phone radiation is not clear. These are electrical systems, so that may be some sort of factor, he wrote in an e-mail.
A few epidemiology studies have reported higher rates of tumors inside the skull among people who use cell phones heavily for 10 years or more. Of particular concern are benign Schwann cell tumors called acoustic neuromas, which affect nerve cells connecting the inner ear with structures inside the brain. These growths can in some instances progress to malignant cancer with time. But other studies have found no evidence of acoustic neuromas or brain tumors in heavy cell phone users.
Samet adds a major challenge now would be to draw a biologically relevant connection between acoustic neuromas and other glial tumors in the brains of humans with Schwann tumors in rat hearts. Even if the hazard is low, billions of people are exposed, she says, alluding to the estimated number of wireless subscriptions worldwide. Cancer monitoring by the institute and other organizations has yet to show increasing numbers of brain tumors in the general population, he says.
We are by no means dismissing the evidence, and the Ramazzini study raises interesting questions. But it has to be factored in with other reports, and this is still work in progress. Epidemiology studies investigating cell phone use patterns with human cancer risk have produced inconsistent results. Some studies enrolled people who already had tumors with suspected links to RF radiation, such as gliomas, acoustic neuromas and salivary gland tumors.
Researchers compared the self-reported cell phone use habits of the cancer patients with those of other people who did not have the same diseases. Based on the evaluation of the currently available information, the FDA believes that the weight of scientific evidence has not linked exposure to radio frequency energy from cell phone use with any health problems at or below the radio frequency exposure limits set by the FCC.
Cell phones emit low levels of non-ionizing radiation when in use. The type of radiation emitted by cell phones is also referred to as radio frequency RF energy.
As stated by the National Cancer Institute, "there is currently no consistent evidence that non-ionizing radiation increases cancer risk in humans.
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