But the weight of the evidence, which is based on larger
studies, has shown no association between cell phone use and brain
cancer. Studies currently in progress such as the European Interphone
Study will provide more information on this subject. For now, the Food
and Drug Administration Center for Devices and Radiological Health and
the Federal Communications Commission offers the following advice to
people concerned about cell phone use and risk:
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 you are
concerned about avoiding even potential risks, you can take a few simple
steps to minimize your exposure to radiofrequency energy (RF). Since
time is a key factor in how much exposure a person receives, reducing
the amount of time spent using a wireless phone will reduce RF exposure.
If you must conduct extended conversations by wireless phone every day,
you could place more distance between your body and the source of the RF,
since the exposure level drops off dramatically with distance. For
example, you could use a headset and carry the wireless phone away from
your body or use a wireless phone connected to a remote antenna.
Background
Recent media attention has focused on a possible link
between cell phone use and brain cancer, originally because of a lawsuit
that alleged such a link. Network news programs ran their own tests of
cell phones, reporting to the public that some of them exceed the
maximum level of emitted radiofrequency (RF) energy allowed by the US
Federal Communications Commission (FCC).
The Cellular Telecommunications & Internet Association estimated that
there were 219 million US cell phone subscribers in mid-2006. Based on
the large and still rapidly growing number of cell phone users, and the
seriousness of brain tumors, this is clearly a topic of wide concern.
This document summarizes what we now know about the carcinogenicity
(cancer-causing potential) of using cell phones.
How do cell phones
work?
Cell phones operate with radio frequencies (RF), a
form of energy located on the electromagnetic spectrum between FM radio
waves and the waves used in microwave ovens, radar, and satellite
stations. Cell phones do not emit ionizing radiation, the type that
damages DNA and is known to have the ability to cause cancer.
Cell phone technology works on a system of geographically separated
zones called "cells." Each cell has its own "base station" that both
receives and emits radio waves. When a call is placed from a cell phone,
a signal is sent from the cell phone antenna to that cell’s base station
antenna. The base station responds to the cell phone signal by assigning
the phone an available RF channel. When the RF channel is assigned,
radio signals are simultaneously received and transmitted, allowing
voice information to be carried between the cell phone and the base. The
base station transfers the call to a switching center, where the call
can be transferred to a local telephone carrier or another cell phone.
There are 2 types of wireless phones:
cordless
mobile
Cordless phones, commonly used in homes, have base units that are
plugged into telephone jacks and wired to a local telephone service;
these are not considered "cell" phones. The question of health risks
associated with cordless phones, which operate at 1/600 the power of
cell phones, has not been raised.
Mobile phones are also known as "cell phones." The antennas of these
phones are integrated into the body of the phone. Because the antenna of
a mobile phone is close to the phone user’s head, mobile phones pose
greater RF exposure than the other types of cordless phones.
How are people
exposed?
Many factors affect the amount of RF to which a person
is exposed. The number of "cells" in a geographical area depends on the
cell phone traffic in that area. For example, large cities may have many
cells per square mile, whereas a less-populated, rural area may have a
single large cell stretching over several square miles. The farther away
a cell phone antenna is from its base station, the higher the power
level needed to maintain the connection. Smaller cells are therefore
associated with much lower exposures.
Each geographical cell has a different number of available channels.
Cell phones operate ideally with the least amount of interference from
neighboring channels. To help achieve the best operation, cell phones
automatically step down to the lowest power level available that still
maintains a connection with the base station. On the other hand, any
physical obstacle, such as buildings or trees, interfering with the
connection forces the base station to increase the power sent to the
phone. Therefore, the amount of power sent from a base station to a
particular cell phone can vary, even within a single call. For
additional information on base stations, please see the American Cancer
Society document, Cellular Phone Towers.
Cell phone makers are required to report the specific absorption rate
(SAR) of their product to the FCC. The SAR is the amount of RF energy
absorbed from the phone into the user's local tissues. The upper limit
of SAR allowed is 1.6 watts per kilogram (W/kg) of body weight. Exposure
to RF also depends on the duration and frequency of cell phone use, with
more use implying more exposure. Finally, older cell phones (analog
models) involve higher exposure than newer, digital equipment.
Do cell phones cause brain cancer?
What studies in humans suggest
Because widespread cell phone use is little more than a decade old,
there has been limited opportunity to examine its long-term health
effects. However, large case-control studies and cohort studies have
compared cell phone use among brain cancer patients and people without
brain cancer. In each of the case-control studies, patients with brain
cancer were compared to people free of brain cancer, in terms of their
past use of cell phones. If the patients reported more cell phone use
than those in the study who did not have brain cancer, and if no other
differences between the 2 groups could account for the brain cancers,
these observations would provide evidence of a possible link between
cell phones and brain cancer. The majority of case-control studies have
yielded similar results:
First, the patients with brain cancer did not report more cell phone use
overall than the controls. This finding was true when all brain cancers
were considered as a group, when individual types of brain cancer were
considered, and when specific locations within the brain were
considered. In fact, most of the studies showed a tendency toward a
lower risk of brain cancer among cell phone uses, for unclear reasons.
Second, none of the studies showed a "dose-response relationship" -- a
tendency for the risk of brain cancer to increase with increasing cell
phone use, which would be expected if cell phone use caused brain
cancer.
Third, the studies did not show a clear link between the side of the
head on which the brain cancer occurred and the side on which the cell
phone was used (with the possible exception of the Swedish study).
Recent results from the Swedish Interphone study of long-term cell phone
use, using a population-based case control design indicate the same
conclusions. There was no association with risk of any of the brain
tumor types studied (glioma or meningioma), or with duration of use,
side of use, or amount of use.
Results of the long-term cohort study, which linked data on all of the
420,095 cell phone users in Denmark between 1982 and 2002 to the Danish
Cancer Registry, agree with the findings of the case-control studies.
Cell phone use, even for more than 10 years, was not associated with an
increased risk of developing brain tumors or cancer overall, nor was
there an association with any brain tumor subtypes or with tumors in any
location within the brain. As in the case-control studies, no link was
found between brain tumor risk and RF dose, as assessed by length of
cell phone use, date since first subscription, age at first
subscription, or type of cell phone used.
However, these published studies have only limited ability to examine
the association between cell phone use and specific subtypes of brain
cancer. One subtype that has been studied is acoustic neuroma, a
relatively rare, slow-growing tumor of the acoustic nerve (which
transmits the sensation of hearing from the ear to the brain) that
occurs in less than one adult per 100,000 people per year. At least 9
epidemiological studies have looked for an association between the use
of cell phones and acoustic neuroma. Results of these studies have been
inconsistent, due largely to variations in study design and statistical
challenges posed by the rarity of these tumors. One of the largest and
most recent studies analyzed data from the 5 northern European
countries, and found no relation of acoustic neuroma risk with cell
phone use, duration of use, or number of calls made. According to the
researchers, "The study suggested there is no substantial risk of
acoustic neuroma in the first decade after starting mobile phone use.
However, an increase in risk after longer term use or after a longer lag
period could not be ruled out."
In summary, there is now considerable epidemiologic evidence that shows
no consistent association between cell phone use and overall risk of
brain cancer. Some uncertainty remains regarding a possible association
with acoustic neuromas. Several large studies now in progress will add
markedly to the evidence within a few years.
What the animal and laboratory evidence suggests
Most but not all laboratory studies have reported a lack of RF-induced
DNA damage. No increase in spontaneous brain tumors was observed in 2
studies of rats exposed to RF. The risk of lymphoma after radiation in
rodents genetically altered to be especially sensitive to cancer-causing
influences was increased following whole-body RF exposure.
What do expert
agencies say?
Based on animal and human evidence like the examples
above, expert agencies have evaluated the cancer-causing potential of
cell phone use.
In October 1999, the Center for Devices and Radiological Health (CDRH),
part of the U.S. Food and Drug Administration (FDA), responded to
increased media focus on cell phones and brain cancer by issuing a
Consumer Update on Mobile Phones (including cell phones). In its
statement, the CDRH stated, "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."
The FCC issued a statement in October 1999 in response to media
assertions that some mobile phones exceed the maximum level of emitted
radiation permitted. Claiming support from the Food and Drug
Administration, the Environmental Protection Agency, the National
Institute for Occupational Safety and Health, and the Occupational
Safety and Health Administration, the FCC stated that its guidelines
"already incorporate a large margin of safety between allowed levels of
exposure and exposure thresholds that have been identified with known
adverse health effects." The excess levels of exposure reported by the
media were "well within that safety margin, and, therefore, there is no
indication of any immediate threat to human health from these phones."
The FCC is currently undertaking new research to verify the safety of RF
levels emitted from mobile phones.
A recent consumer information document issued jointly by the FDA and FCC
reaches the same conclusions:
The available scientific evidence does not show that any health problems
are associated with using wireless phones. There is no proof, however,
that wireless phones are absolutely safe. Wireless phones emit low
levels of radiofrequency energy (RF) in the microwave range while being
used. They also emit very low levels of RF when in the stand-by mode.
Whereas high levels of RF can produce health effects (by heating
tissue), exposure to low-level RF that does not produce heating effects
causes no known adverse health effects. Many studies of low level RF
exposures have not found any biological effects. Some studies have
suggested that some biological effects may occur, but such findings have
not been confirmed by additional research. In some cases, other
researchers have had difficulty in reproducing those studies, or in
determining the reasons for inconsistent results.
The United States Environmental Protection Agency (EPA), National
Toxicology Program (NTP), and the International Agency for Research on
Cancer (IARC), 3 of the main exposure classifying agencies, have not
evaluated the carcinogenicity (cancer-causing potential) of cell phone
use.
Do cell phones
cause any other health problems?
To date, no claims have been made that cell phones are
responsible for any other health problems. A small epidemiologic study
from Germany found an association between uveal melanoma (a rare form of
eye cancer) and exposure to mobile phones and other RF-transmitting
devices, but this has not yet been examined in other studies. However,
evidence has shown that the use of cell phones while driving increases
the risk of automobile crashes. Another concern, without much evidence
one way or the other, is that cell phones may interfere with medical
electronic devices such as pacemakers and insulin pumps.
Can I do
anything to lower my exposure to RF from cell phones?
Cell phone users who wish to lower exposure to RF
emissions from cell phones may choose to use a corded or cordless
earpiece when using their phone. Using an earpiece moves the device away
from the user's head, which decreases the amount of radiation that
reaches the body. Corded earpieces emit virtually 0 RF emissions, and
Bluetooth® earpieces have an SAR value of around 0.001 watts/kg (less
than one thousandth the SAR limit for cell phones as set by the FDA and
FCC).
Cell phone
users can also choose a phone with a low SAR value. According to the
FDA,
Information on SAR for a specific phone model can be
obtained for many recently manufactured phones using the FCC
identification (ID) number for that model. The FCC ID number is usually
printed somewhere on the case of the phone. Sometimes it may be
necessary to remove the battery pack to find the number. Once you have
the ID number, go to the following Web address: www.fcc.gov/oet/fccid.
On this page, you will see instructions for entering the FCC ID number.
The FDA also provides information
regarding hands-free kits and accessories that claim to shield the head
from RF exposure:
Since there are no known risks from exposure to RF
emissions from wireless phones, there is no reason to believe that
hands-free kits reduce risks. Hands-free kits can be used with wireless
phones for convenience and comfort. These systems reduce the absorption
of RF energy in the head because the phone, which is the source of the
RF emissions, will not be placed against the head. On the other hand, if
the phone is mounted against the waist or other part of the body during
use, then that part of the body will absorb more RF energy.
Some products that claim to shield the user from RF absorption use
special phone cases, while others involve nothing more than a metallic
accessory attached to the phone. Studies have shown that these products
generally do not work as advertised. Unlike 'hands-free' kits, these
so-called 'shields' may interfere with proper operation of the phone.
The phone may be forced to boost its power to compensate, leading to an
increase in RF absorption. |
