Cell Phones and Cancer Risk

[BSHC]

 
 Cell Phones and Cancer Risk

Key Points
Cell phones emit radiofrequency (RF) energy, which is another name for radio waves (see Questions 1 and 2).
Research suggests that the amount of RF energy produced by cell phones is too low to cause significant tissue heating or an increase in body temperature (see Question 2).
Concerns have been raised that RF energy from cell phones may pose a cancer risk to users (see Questions 1 and 2).
Researchers are studying tumors of the brain and central nervous system and other sites of the head and neck because cell phones are typically held next to the head when used (see Question 5).
Research studies have not shown a consistent link between cell phone use and cancer. A large international study (Interphone) published in 2010 found that, overall, cell phone users have no increased risk for two of the most common types of brain tumor—glioma and meningioma. For the small proportion of study participants who reported spending the most total time on cell phone calls there was some increased risk of glioma, but the researchers considered this finding inconclusive (see Questions 6 and 7).
Why is there concern that cell phones may cause cancer or other health problems?

There are three main reasons why people are concerned that cell phones (also known as "wireless" or "mobile" telephones) may cause certain types of cancer or other health problems:

Cell phones emit radiofrequency (RF) energy (radio waves), which is a form of radiation that has been under study for many years for its effects on the human body (1).

Cell phone use began in Europe in the 1980s but did not come into widespread use in the United States until the 1990s. The technology is constantly evolving. The recent Interphone study is one of the few large studies of the effects of RF energy from cell phones on the human body.

The number of cell phone users has increased rapidly. As of 2009, there were more than 285 million subscribers to cell phone service in the United States, according to the Cellular Telecommunications and Internet Association. This is an increase from 110 million users in 2000 and 208 million users in 2005.
For these reasons, it is important to learn whether RF energy from cell phones affects human health.

What is RF energy and how can it affect the body?

RF energy is a form of electromagnetic radiation.

Electromagnetic radiation can be divided into two types: Ionizing (high-frequency) and non-ionizing (low-frequency) (2). RF energy is a type of non-ionizing electromagnetic radiation. Ionizing radiation, such as that produced by x-ray machines, can pose a cancer risk. There is currently no conclusive evidence that non-ionizing radiation emitted by cell phones is associated with cancer risk (2).

Studies suggest that the amount of RF energy produced by cell phones is too low to cause significant tissue heating or an increase in body temperature. However, more research is needed to determine what effects, if any, low-level non-ionizing RF energy has on the body and whether it poses a health danger (2).

How is a cell phone user exposed to RF energy?

A cell phone's main source of RF energy is produced through its antenna. The antenna of newer hand-held cell phones is in the handset, which is typically held against the side of the head when the telephone is in use. The closer the antenna is to the head, the greater a person's expected exposure to RF energy. The amount of RF energy absorbed by a person decreases significantly with increasing distance between the antenna and the user. The intensity of RF energy emitted by a cell phone depends on the level of the signal (1).

When a call is placed from a cell phone, a signal is sent from the antenna of the phone to the nearest base station antenna. The base station routes the call through a switching center, where the call can be transferred to another cell phone, another base station, or the local land-line telephone system. The farther a cell phone is from the base station antenna, the higher the power level needed to maintain the connection. This distance determines, in part, the amount of RF energy exposure to the user.

What determines how much RF energy a cell phone user experiences?

A cell phone user’s level of exposure to RF energy depends on several factors, including:

The number and duration of calls.
The amount of cell phone traffic at a given time.
The distance from the nearest cellular base station.
The quality of the cellular transmission.
The size of the handset.
For older phones, how far the antenna is extended.
Whether or not a hands-free device is used.

What parts of the body may be affected during cell phone use?

There is concern that RF energy produced by cell phones may affect the brain and other tissues in the head because hand-held cell phones are usually held close to the head. Researchers have focused on whether RF energy can cause malignant (cancerous) brain tumors, such as gliomas (cancers of the brain that begin in glial cells, which surround and support the nerve cells), as well as benign (noncancerous) tumors, such as acoustic neuromas (tumors that arise in the cells of the nerve that supplies the ear) and meningiomas (tumors that occur in the meninges , which are the membranes that cover and protect the brain and spinal cord) (1). The salivary glands also may be exposed to RF energy from cell phones held close to the head.

What studies have been done, and what do they show?
Numerous studies have investigated the relationship between cell phone use and the risk of developing malignant and benign brain tumors.

The most significant study of long-term use is the 13-country Interphone study, which is a multinational consortium of case-control studies. Interphone was coordinated by the International Agency for Research on Cancer (IARC) (3). The primary objective of the Interphone study was to assess whether RF energy exposure from cell phones is associated with an increased risk of malignant or benign brain tumors and other head and neck tumors. Participating countries included Australia, Canada, Denmark, Finland, France, Germany, Israel, Italy, Japan, New Zealand, Norway, Sweden, and the United Kingdom (4).

Interphone researchers reported that, overall, cell phone users have no increased risk for two of the most common types of brain tumor―glioma and meningioma. In addition, they found no evidence of increasing risk with progressively increasing number of calls, longer call time, or years since beginning cell phone use. For the small proportion of study participants who reported spending the most total time on cell phone calls, there was some increased risk of glioma, but the researchers considered this finding inconclusive. The study was published online May 17, 2010, in the International Journal of Epidemiology (5). 

Additional studies have investigated the risk of developing glioma, meningioma, and acoustic neuroma. Results from the majority of these studies have found no association between hand-held cell phone use and the risk of brain cancer (6–11); however, some, but not all, studies have suggested slightly increased risks for certain types of brain tumors (12, 13). 

Two reports published in November 2004 by researchers from individual countries that participated in the Interphone study described the results of assessments of cell phone use and the risk of acoustic neuroma. One report described a Danish case-control study that showed no increased risk of acoustic neuroma in long-term (10 years or more) cell phone users compared with short-term users, and there was no increase in the incidence of tumors on the side of the head where the phone was usually held (14). The other report described a Swedish study that examined similar populations and found a slightly elevated risk of acoustic neuroma in long-term cell phone users but not in short-term users (15).

A pooled analysis of data from Denmark, Finland, Norway, Sweden, and the United Kingdom did not find relationships between the risk of acoustic neuroma and the duration of cell phone use, cumulative hours of use, or number of calls; however, the risk of a tumor on the same side of the head as the reported phone use was higher among persons who had used a cell phone for 10 years or more. Some other studies have reported similar findings (16). However, there is concern that people with a tumor on one side of their head might be more likely to report phone use on that side (12).

Other reports from the Danish and Swedish researchers who collaborated in the Interphone study investigated whether a relationship exists between cell phone use and the risk of meningioma or glioma. These studies compared individuals with meningioma or glioma with a control group of disease-free individuals and found no link between these conditions and cell phone use (17, 18). 

In addition, pooled analyses of data from four Nordic countries and the United Kingdom did not show overall associations between the risk of glioma or meningioma and the cumulative hours of cell phone use or the number of calls (19, 20). There was a slightly increased risk of glioma occurring on the same side of the head as the reported phone use among persons who used a cell phone for at least 10 years (19).

In an attempt to avoid the issue of biases associated with case-control studies, researchers defined a cohort of 420,095 persons in Denmark with cell phone subscriptions and linked this roster with the Danish Cancer Registry to identify brain tumors occurring in this population (10, 11). Cell phone use was not associated with glioma, meningioma, or acoustic neuroma, even among persons who had been subscribers for 10 or more years. Cell phone service subscription does not necessarily relate directly to cell phone use, duration, and frequency of use. A listed subscriber may not be the primary user of the phone. However, this type of prospective study has the advantage of not having to rely on people’s ability to remember past cell phone use.

Incidence data from the Surveillance, Epidemiology and End Results (SEER) Program of the National Cancer Institute (NCI), which is part of the National Institutes of Health (NIH), show no increase in the age-adjusted incidence of brain and other nervous system cancers between 1987 and 2007, despite the dramatic increase in the use of cell phones (21). NCI continues to monitor cancer incidence data to detect any change in the rates of new cases of brain cancer. If cell phones play a role in the risk of brain cancer, one would expect to see an increase in rates because average monthly hours of cell phone use have increased regularly for the past decade in the United States.

There are very few studies of the possible relationship between cell phone use and tumors other than those of the brain and central nervous system (22–25).

What large studies has NCI conducted on cell phones and what have they found?
NCI began a comprehensive study of possible environmental and genetic causes of malignant and benign brain tumors in 1994. The findings were published in 2001 (http://www.cancer.gov/newscenter/cellphassoc) and were part of a comprehensive study to address a variety of possible risk factors for brain tumors. The study included 782 brain tumor cases and 799 controls from three medical institutions: St. Joseph’s Hospital and Medical Center in Phoenix, Brigham and Women’s Hospital in Boston, and Western Pennsylvania Hospital in Pittsburgh. The study included brain tumor patients diagnosed with glioma (489 cases), meningioma (197 cases), or acoustic neuroma (96 cases). The control subjects were people who were admitted for a variety of non-cancerous conditions to the same hospitals as the brain tumor patients. The control subjects were matched with the case subjects by hospital, sex, race, age, and distance of residence from the hospital. The study was restricted to adults who were 18 or older who received care at one of the participating hospitals, resided within 50 miles of the hospital, and could understand English or Spanish. Data collection began in 1994 and was completed in 1998.

The study found no indication of higher brain tumor risk among persons who had used hand-held cell phones compared with those who had not used them. More importantly, there was no evidence of increasing risk with increasing years of use or average minutes of use per day, nor did brain tumors among cell phone users tend to occur more often than expected on the side of the head on which the person reported using their phone. Specifically, there was no indication of increased risk associated with use of a cell phone for 1 hour or more per day, for 5 or more years, or for cumulative use of more than 100 hours. These findings pertain to all three tumor types considered (glioma, meningioma, and acoustic neuroma).

The results of this study pertain primarily to patterns of cell phone use in the United States during the early to mid-1990s. During the period of this study, there was no evidence that use of hand-held cell phones caused tumors of the brain and central nervous system. The findings suggest that, if there was any increase in risk, it was small, particularly for malignant tumors (glioma).

What studies are being done to help understand whether there is a biologic basis for cell phone radiation exposure to cause cancer?

Another part of the NIH, the National Institute of Environmental Health Sciences (NIEHS), is carrying out a study of risks related to exposure to RF radiation (the type used in cell phones) in highly specialized labs that can specify and control sources of radiation and measure their effects on rodents.

Gliomas are the most common brain cancers being studied. What other brain tumors are being studied?

NCI’s Division of Cancer Control and Population Sciences (DCCPS) is funding a population-based, case-control study of meningioma (which accounts for up to 25 percent of all primary brain tumors) in Connecticut, Massachusetts, North Carolina, Texas, and the San Francisco Bay area of California. This study represents the first concentrated effort to examine environmental and genetic risk factors for meningioma. The researchers are collecting information from 1,520 adults diagnosed with meningioma (case subjects) and 1,520 individuals without the disease (control subjects) matched by sex, age, and other characteristics to amass information on two main categories of risk—exposure to ionizing radiation and hormones—as well as on family history of the disease and other tumors, cell phone use, head trauma, outcome, and quality of life.

Why are the results of some, but not most, studies inconsistent?

The Interphone study suggests that overall there is no cancer risk from cell phones.

There are several reasons for the discrepancies between other studies:

Information about cell phone use, including the frequency of use and the duration of calls, has largely been assessed through questionnaires. The completeness and accuracy of the data collected during such interviews is dependent on the memory of the responding individuals. In case-control studies, individuals with brain tumors may remember cell phone use differently from healthy individuals, which can result in a problem known as recall bias.

Digital cell phones have been in common use for less than a decade in the United States, and cellular technology continues to change (1). What was called 2G, or second-generation technology, was introduced in the United States in the 1990s. It was not until 3G, or third-generation technology, was introduced in 2001 that cell phone use became widely accepted in this country. Although older studies eval‎uated RF energy exposure from analog telephones, most cell phones today use digital technology, which operates at a different frequency and a lower power level than analog phones.

The interval between exposure to a carcinogen and the clinical onset of a tumor may be many years or decades. Scientists have been unable to monitor large numbers of cell phone users for the length of time it might take for brain tumors to develop (1).

Epidemiologic studies of cell phone use and brain cancer risk lack verifiable data about cumulative RF energy exposure over time (the total amount of RF energy individuals have encountered). These studies are also vulnerable to errors in the reporting of RF exposure by study participants (26, 27). In addition, study participation rates are frequently different between those with cancer and those without cancer in brain tumor studies, a problem known as participation bias. Some studies have indicated greater participation by individuals diagnosed with brain tumors compared with control subjects, and participation rates may be related to cell phone use.

The use of “hands-free” wireless technology is increasing and may alter cell phone RF energy exposure.

With the publication of the Interphone study, research has fairly consistently demonstrated that there is not a link between cell phone use and cancer, but scientists caution that further surveillance, especially of heavy users and children and adolescents, is needed before definite conclusions can be drawn (1, 28).

Are any prospective studies or other types of studies that don’t involve recall bias being conducted?
A large, prospective cohort study of cell phone use and its possible long-term health effects was launched in Europe in March 2010. This study, known as COSMOS, will enroll approximately 250,000 cell phone users age 18 or older and will follow them for 20 to 30 years. Participants in COSMOS will complete a questionnaire about their health, lifestyle, and current and past cell phone use. This information will be supplemented with information from health records and cell phone records. More information about the COSMOS study is available at http://www.ukcosmos.org/index.html on the Internet.

Although recall bias is minimized in studies that link to cell phone records, such studies face other problems. For example, it is impossible to know who is using the cell phone or whether they are using multiple phones and, to a lesser extent, if multiple users of a single phone are represented on one bill.

Do children have a higher risk of developing cancer due to cell phone use than adults?

There are currently no data on cell phone use and risk of cancer in children. No published studies to date have included children. Cell phone use by children and adolescents is increasing rapidly, and they are likely to accumulate many years of exposure during their lives (1). In addition, children may be at greater risk because their nervous systems are still developing at the time of exposure. A large case-control study of childhood brain cancer in several Northern European countries is in progress. Researchers from the Centre for Research in Environmental Epidemiology in Spain are conducting an international study—Mobi-Kids—to eval‎uate risk from new communications technologies (including cell phones) and other environmental factors in young people ages 10 to 24. More information about the Mobi-Kids study is available at http://www.mbkds.com on the Internet.

What can cell phone users do to reduce their exposure to RF energy?

The Food and Drug Administration and the Federal Communications Commission (FCC) have suggested some steps that cell phone users can take if they are concerned about potential health risks (2, 29):

Reserve the use of cell phones for shorter conversations, or for times when a conventional phone is not available.

Switch to a type of cell phone with a hands-free device that will place more distance between the phone and the head of the user.

Hands-free kits reduce the amount of RF energy exposure to the head because the antenna, which is the source of RF energy, is not placed against the head.

Where can I find more information about RF energy from my cell phone?

The FCC provides information about the specific absorption rate (SAR) of cell phones produced and marketed within the last 1 to 2 years. The SAR corresponds to the relative amount of RF energy absorbed into the head of a cell phone user (30). Consumers can access this information using the phone’s FCC ID number, which is usually located on the case of the phone, and the FCC’s ID search form, which is located at http://www.fcc.gov/oet/ea/fccid on the Internet.

What are other sources of RF energy?

The most common use of RF energy is for telecommunications (2). In the United States, cell phones currently operate in a frequency range of about 1,800 to 2,200 megahertz (MHz) (1). In this range, the electromagnetic radiation produced is in the form of non-ionizing RF energy. Cordless phones (phones that have a base unit connected to the telephone wiring in a house) often operate at radio frequencies similar to those of cell phones; however, since cordless phones have a limited range and require a nearby base, their signals are generally much less powerful than those of cell phones. Among other RF energy sources, AM/FM radios and VHF/UHF televisions operate at lower radio frequencies than cell phones, whereas sources such as radar, satellite stations, magnetic resonance imaging (MRI) devices, industrial equipment, and microwave ovens operate at somewhat higher radio frequencies (2).

How common is brain cancer and has the incidence of brain cancer changed over time?

Brain cancer incidence and mortality (death) rates have changed little in the past decade. In the United States, 22,070 new diagnoses and 12,920 deaths from brain cancer were estimated for 2009.

The 5-year survival rate for brain cancers diagnosed from 1999 to 2006 was 36.3 percent (21). This means that 36.3 out of every 100 persons diagnosed with brain cancer today will survive at least 5 years.

The risk of developing brain cancer increases with age; the incidence rate from 2003 to 2007 for people under age 65 was 4.6 for every 100,000 persons in the U.S. population, compared with 19.4 for every 100,000 persons age 65 or older (21).

Selected References

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U.S. Federal Communications Commission (2009). Wireless. Washington, D.C. Retrieved May 17, 2010, from: http://www.fcc.gov/cgb/cellular.html.

U.S. Federal Communications Commission (2009). Cellular Telephone Specific Absorption Rate (SAR). Retrieved May 17, 2010, from: http://www.fcc.gov/cgb/sar.

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Related NCI materials and Web pages:

National Cancer Institute Fact Sheet 3.46, Magnetic Field Exposure and Cancer: Questions and Answers
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Cancer Causes and Risk Factors Home Page
(http://www.cancer.gov/cancertopics/prevention-genetics-causes/causes)
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