- Why is there concern that cellular telephones may cause
cancer?
There are three main reasons why people are concerned that cellular telephones
(also known as “wireless” or “mobile” telephones)
may cause certain types of cancer.
- Cellular telephones emit radiofrequency (RF) energy (radio waves), which
is a form of radiation
and is under investigation for its effects on the human body (1).
- Cellular telephone technology is relatively new and is still changing,
so there are few long-term studies of the effects of RF energy from cellular
telephones on the human body (1).
- The number of cellular telephone users has increased rapidly. As of December
2007, there were more than 255 million subscribers to cellular telephone
service in the United States, according to the Cellular Telecommunications
and Internet Association (CTIA). 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 cellular
telephones 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 form
of non-ionizing electromagnetic radiation. Ionizing
radiation, such as that produced by x-ray
machines, can pose a cancer risk at high levels of exposure. However, it is
not known whether the non-ionizing radiation emitted by cellular telephones
is associated with cancer risk (2).
Studies suggest that the amount of RF energy produced by cellular phones
is too low to produce 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 cellular telephone user exposed to RF energy?
A cellular telephone’s main source of RF energy is produced through
its antenna. The antenna of a hand-held cellular telephone 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 is 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 cellular telephone depends on
the level of the signal sent to or from the nearest base station (1).
When a call is placed from a cellular telephone, 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 cellular telephone, another base station, or to the local land-line
telephone system. The farther a cellular telephone 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 cellular telephone
user experiences?
A cellular telephone user’s level of exposure to RF energy depends
on several factors, including:
• the number and duration of calls
• the amount of cellular telephone traffic at a given time
• the distance from the nearest cellular base station
• the quality of the cellular transmissions
• how far the antenna is extended
• the size of the handset
• whether or not a hands-free device is used
- What parts of the body may be affected during cellular telephone
use?
There is concern that RF energy produced by cellular phones may affect the
brain and nervous system tissue in the head because hand-held cellular telephones
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 cellular phones held close
to the head.
- What studies have been done and what do they show?
Numerous studies have investigated the relationship between cellular telephone
use and the risk of developing brain cancer, but results from long-term studies
are still limited.
Several studies have investigated the risk of developing three types of brain
tumors, namely glioma, meningioma, and acoustic neuroma.
Results from the majority of these studies have found no association between
hand-held cellular telephone use and the risk of brain cancer (3–8);
however, some, but not all, long-term studies have suggested slightly increased
risks for certain types of brain tumors (9, 10).
Further evaluation of long-term exposures (more than 10 years) is needed.
A series of multinational case-control studies (comparing individuals who
have a disease or condition [case subjects] with a similar group of people
who do not have the disease or condition [control
subjects]), collectively known as the INTERPHONE study, are being coordinated
by the International Agency for Research on Cancer (IARC) (11).
The primary objective of these studies is to assess whether RF energy exposure
from cellular telephones is associated with an increased risk of malignant
or benign brain tumors and other head and neck tumors. Participating countries
include Australia, Canada, Denmark, Finland, France, Germany, Israel, Italy,
Japan, New Zealand, Norway, Sweden, and the United Kingdom (12).
Several reports describing data from individual countries have been published
independently by researchers involved in the INTERPHONE study; however, these
reports represent only a portion of the entire INTERPHONE dataset. The combined
INTERPHONE analysis is underway and will provide more comprehensive and stable risk estimates
than analyses from the individual countries.
Two reports published in November 2004 by researchers from individual countries
that are participating in the INTERPHONE study described results of assessments
of cellular telephone 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) cellular telephone 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 (13).
The other report described a Swedish study that examined similar populations
and found a slightly elevated risk of acoustic neuroma in long-term cellular
telephone users but not in short-term users (14).
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 (9).
Other reports from the Danish and Swedish researchers who are collaborating
in the INTERPHONE study investigated whether a relationship exists between
cellular telephone use and the risk of meningioma or glioma. These studies
from Denmark and Sweden compared individuals with meningioma or glioma with
a control
group of disease-free individuals and found no link between these conditions
and cellular telephone use (15, 16).
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 (17,
18). 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 (17).
In an attempt to avoid the issue of biases associated with case-control studies,
investigators defined a cohort of 420,095 persons in Denmark with cellular
phone subscriptions and linked this roster with the Danish Cancer Registry
to identify brain tumors occurring in this population (7,
8). Cellular phone use was not associated with glioma, meningioma,
or acoustic neuroma, even among persons who had been subscribers for 10 or
more years. This type of prospective
study has the advantage of not having to rely on peoples’ ability to
remember past cellular phone use.
Incidence data from the Surveillance, Epidemiology
and End Results (SEER) program of the National
Cancer Institute have shown no increase between 1987 and 2005 in the age-adjusted
incidence of brain or other nervous system cancers despite the dramatic increase
in use of cellular telephones (19).
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 (20–23).
- Why are the results of the studies inconsistent?
There are several reasons for the discrepancies between studies:
- Information about cellular telephone 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 cellular telephone use
differently from healthy individuals, which can result in a problem known
as recall bias.
- Cellular telephone use is relatively new (mostly since the 1990s), and
cellular technology continues to change (1). Although
older studies evaluated RF energy exposure from analog telephones, most
cellular telephones today use digital technology, which operates at a different
frequency and 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 cohorts of cellular telephone users for the length of time
it might take for brain tumors to develop (1).
- Other limitations of current epidemiologic studies on cellular telephone
use and brain cancer include a lack of verifiable data regarding cumulative
RF energy exposure over time (the total amount of RF energy individuals
have encountered) and potential errors in the exposure information reported
by study participants after individuals are diagnosed
with cancer, a problem known as reporting bias (24,
25). In addition, participation rates are frequently
different between case subjects and control subjects in brain tumor studies,
a problem known as participation bias. Some studies have indicated
greater participation by individuals diagnosed with brain tumors compared
with controls, and participation rates may be related to cellular phone
use.
- The use of “hands-free” wireless technology, such as Bluetooth®,
is increasing and may contribute to variation in cellular phone exposures.
Although research has not consistently demonstrated a link between cellular
telephone use and cancer, scientists still caution that further surveillance
is needed before conclusions can be drawn about the risk of cancer from cellular
telephones (1).
- Do children have a higher risk of developing cancer due
to cellular telephone use than adults?
There are currently no data on cellular telephone use and risk in children
because no published studies to date have included children. Cellular telephone
use is increasing rapidly in children and adolescents, 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.
- What can cellular telephone users do to reduce their exposure
to RF energy?
The U.S. Food and Drug
Administration (FDA) has suggested some steps that cellular telephone users
can take if they are concerned about potential health risks from cellular
telephones:
- Reserve the use of cellular telephones for shorter conversations, or
for times when a conventional phone is not available.
- Switch to a type of cellular telephone with a hands-free device that
will place more distance between the antenna and the head of the phone 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
(2). However, most studies conducted on cellular telephone
use and cancer risk have focused on hand-held models not equipped with hands-free
systems because they deliver the most RF energy to the user’s head.
- Where can I find more information about RF energy exposure?
The Federal Communications Commission (FCC), which regulates interstate and
international communications, provides consumers with information about human
exposure to RF energy from cellular telephones and other devices at http://www.fcc.gov/oet/rfsafety
on the Internet. This Web page includes information about the specific absorption
rate (SAR) of cellular telephones 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 cellular telephone user. Consumers can access this information
using the phone’s FCC ID number, which is usually located on the case
of the phone.
- What are other sources of RF energy?
The most common use of RF energy is for telecommunications (2).
In the United States, cellular telephones 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.
AM/FM radios, VHF/UHF televisions, and cordless telephones (telephones that
have a base unit connected to the telephone wiring in a house) operate at
lower radio frequencies than cellular telephones. Other sources of RF energy,
including radar, satellite stations, magnetic
resonance imaging (MRI)
devices, industrial equipment, and microwave ovens, operate at somewhat higher
radio frequencies (2).