Cellular
(cell) phones first became widely available in the United
States
Cell
phones (including smartphones) give off a form of energy known
as radiofrequency (RF) waves, so some concerns have been raised about the
safety of cell phone use. With respect to cancer, concern focuses on whether
cell phones might increase the risk of brain tumors or other tumors in the head
and neck area.
How do cell phones work?
Cell phones
work by sending signals to (and receiving them from) nearby cell
towers (base stations) using RF waves. This is a form of electromagnetic
energy that falls between FM radio waves and microwaves. Like FM radio waves,
microwaves, visible light, and heat, RF waves are a form of non-ionizing radiation.
They don’t have enough energy to cause cancer by directly damaging the DNA inside cells. RF waves are different from stronger (ionizing) types of
radiation such as x-rays, gamma rays, and ultraviolet (UV)
light, which can break the chemical bonds in DNA.
At very high levels, RF waves can
heat up body tissues. (This is the basis for how microwave ovens work.) But the
levels of energy given off by cell phones are much lower, and are not enough to
raise temperatures in the body.
How are people exposed?
TheRF waves from cell phones come from the antenna, which is part of the body of a
hand-held phone. The waves are strongest at the antenna and lose energy quickly
as they travel away from the phone. The phone is typically held against the
side of the head when in use. The closer the antenna is to the head, the
greater a person’s expected exposure to RF energy. The body tissues closest to
the phone absorb more energy than tissues farther away.
Many
factors can affect the amount of RF energy to which a person is exposed,
including:
- The amount of time the person is on the phone.
- Whether or not the person is using the
speaker mode on the phone or a hands-free device. Using one of these
allows the phone to be held away from the head.
- The distance and path to the nearest cell
phone tower. Cell phones adjust their power to use the minimum amount for a
good signal. Being farther away from the tower requires more energy to get
a good signal, as does being inside a building.
- The amount of cell phone traffic in the
area at the time. Higher traffic may require more energy to get a good
signal.
- The model of phone being used. Different phones give
off different amounts of energy.
What is the specific absorption rate (SAR) of a
cell phone?
The
amount of RF energy absorbed from the phone into the user’s body is known as
thespecific absorption rate (SAR).
Different cell phones have different SAR levels. Cell phone makers are required
to report the maximum SAR level of their product to the US Federal
Communications Commission (FCC). This information can often be found on the
manufacturer’s website or in the user manual for the phone. The upper limit of
SAR allowed in the United States
But
according to the FCC, comparing SAR values between phones can be misleading.
The listed SAR value is based only on the phone operating at its highest power,
not on what users would typically be exposed to with normal phone use. The
actual SAR value during use varies based on a number of factors, so it’s
possible that a phone with a lower listed SAR value might actually expose a
person to more RF energy than one with a higher listed SAR value in some cases.
Do cell phones cause tumors?
Because
cell phones usually are held near the head when being used, the main concern
has been whether they might cause or contribute to tumors in this area,
including:
- Malignant (cancerous) brain tumors such as gliomas
- Non-cancerous tumors of the brain such as meningiomas
- Non-cancerous tumors of the nerve connecting the
brain to the ear (vestibular schwannomas, also known as acoustic neuromas)
- Non-cancerous tumors of the salivary glands
A
few studies have also looked at possible links to other types of cancer, such
as skin
cancer and testicular cancer.
Researchers
use 2 main types of studies to try to determine if something might cause
cancer.
Lab studies: Lab studies usually
expose animals to something like RF energy to see if it causes tumors or other
health problems. Researchers might also expose normal cells in a lab dish to RF
energy to see if it causes the types of changes that are seen in cancer cells.
It’s not always clear if the results from these types of studies will apply to
humans, but lab studies allow researchers to carefully control for other
factors that might affect the results and to answer some basic science
questions.
Studies in people: Another type
of study looks at cancer rates in different groups of people. Such a study
might compare the cancer rate in a group exposed to something like cell phone
use to the rate in a group not exposed to it, or compare it to what the
expected cancer rate would be in the general population. But sometimes it can
be hard to know what the results of these studies mean, because many other
factors that might affect the results are hard to account for.
In
most cases neither type of study provides enough evidence on its own to show if
something causes cancer in people, so researchers usually look at both
lab-based and human studies.
What do lab studies suggest?
As
noted above, the RF waves given off by cell phones don’t have enough energy to
damage DNA directly or to heat body tissues. Because of this, it’s not clear
how cell phones might be able to cause cancer. Most studies done in the lab
have supported the idea that RF waves do not cause DNA damage.
Some
scientists have reported that the RF waves from cell phones produce effects in
human cells (in lab dishes) that might possibly help tumors grow. However,
several studies in rats and mice have looked at whether RF energy might promote
the development of tumors caused by other known carcinogens (cancer-causing
agents). These studies did not find evidence of tumor promotion.
A
large study by the US National Toxicology Program (NTP) exposed large groups of
lab rats and mice to RF energy over their entire bodies for about 9 hours a
day, starting before birth and continuing for up to 2 years (which is the
equivalent of about 70 years for humans, according to NTP scientists). In a
draft report of the final results (issued in February 2018), the study found an
increased risk of tumors called malignant schwannomas of the heart in male rats
exposed to RF radiation. But some aspects of this study make it hard to know
just how well these results might be applied to cell phone use in people. For
example, there was no increased risk among female rats or among male or female
mice in the study. The doses of RF radiation in the study were also generally
higher than those used in cell phones (ranging from 1.5 W/kg to 6 W/kg in rats,
and 2.5 W/kg to 10 W/kg in mice), the animals’ entire bodies were exposed, and
the amount of time they were exposed was longer than most people typically
spend on the phone each day. The male rats in the study exposed to RF waves
also lived longer, on average, than the rats who were not exposed, for unclear
reasons. Still, the results add to the evidence that cell phone signals might
potentially impact human health.
A
recent small study in people has shown that cell phones may also have some
other effects on the brain, although it’s not clear if they’re harmful. The
study found that when people had an active cell phone held up to their ear for
50 minutes, brain tissues on the same side of the head as the phone used more
glucose than did tissues on the other side of the brain. Glucose is a sugar
that normally serves as the brain’s fuel. Glucose use goes up in certain parts
of the brain when it is in use, such as when we are thinking, speaking, or
moving. The possible health effect, if any, from the increase in glucose use
from cell phone energy is unknown.
What do studies in humans suggest?
Several
dozen studies have looked at possible links between cell phone use and tumors.
Most of these studies have focused on brain tumors. Many of these have been
case-control studies, in which patients with brain tumors (cases) were compared
to people free of brain tumors (controls), in terms of their past cell phone
use.
These studies have
had mixed results:
These
studies have had mixed results:
- In most studies patients with brain tumors do not
report more cell phone use overall than the controls. This finding is true
when all brain tumors are considered as a group, or when specific types of
tumors are considered.
- Most studies do not show a “dose-response
relationship,” which would be a tendency for the risk of brain tumors to
be higher with increasing cell phone use. This would be expected if cell
phone use caused brain tumors.
- Most studies do not show that brain tumors occur more
often on the side of the head where people hold their cell phones. This
might also be expected if cell phone use caused brain tumors.
- Some studies have found a possible link. For example,
several studies published by the same research group in
Three large studies
deserve special mention:
The INTERPHONE study
The
13-country INTERPHONE study, the largest case-control study done to date,
looked at cell phone use among more than 5,000 people who developed brain
tumors (gliomas or meningiomas) and a similar group of people without tumors.
Overall, the study found no link between brain tumor risk and the frequency of
calls, longer call time, or cell phone use for 10 or more years. There was a
suggestion of a possible increased risk of glioma, and a smaller suggestion of
an increased risk of meningioma, in the 10% of people who used their cell
phones the most. But this finding was hard to interpret because some people in
the study reported implausibly high cell phone use, as well as other issues.
The researchers noted that the shortcomings of the study prevented them from
drawing any firm conclusions, and that more research was needed.
Another
part of the INTERPHONE study compared more than 1,000 people with acoustic
neuromas to more than 2,000 people without tumors, who served as matched
controls. As with gliomas and meningiomas, there was no overall link between
cell phone use and acoustic neuromas. There was again a suggestion of a
possible increased risk in the 10% of people who used their cell phones the
most, but this was hard to interpret because some people reported implausibly
high cell phone use, as well as other issues.
The Danish cohort study
A
large, long-term study has been comparing all of the people in Denmark
This
type of study (following a large group of people going forward in time and not
relying on people’s memories about cell phone use) is generally thought to be
stronger than a case-control study.
But
this study also has some drawbacks. First, it is based only on whether or not
people had a cell phone subscription at the time. It didn’t measure how often
these people used their phones (if at all), or if people who didn’t have a
subscription used someone else’s phone. There are also limits as to how well
this study might apply to people using cell phones today. For example, while
the cell phones used at the time of the study tended to require more power than
modern cell phones, people also probably used the phones quite a bit less than
people use their phones today.
The Million Women Study
A
large prospective (forward-looking) study of nearly 800,000 women in the UK
All studies done so far have limitations
In
summary, most studies of people published so far have not found a link between
cell phone use and the development of tumors. However, these studies have had
some important limitations that make them unlikely to end the controversy about
whether cell phone use affects cancer risk.
First,
studies have not yet been able to follow people for very long periods of time.
When tumors form after a known cancer-causing exposure, it often takes decades
for them to develop. Because cell phones have been in widespread use for only
about 20 years in most countries, it is not possible to rule out future health
effects that have not yet appeared.
Second,
cell phone usage is constantly changing. People are using their cell phones
much more than they were even 10 years ago, and the phones themselves are very
different from what was used in the past. This makes it hard to know if the
results of studies looking at cell phone use in years past would still apply
today.
Third,
most of the studies published so far have focused on adults, rather than
children. (One case-control study looking at children and teens did not find a
significant link to brain tumors, but the small size of the study limited its
power to detect modest risks.) Cell phone use is now widespread even among
younger children. It is possible that if there are health effects, they might
be more pronounced in children because their bodies might be more sensitive to
RF energy. Another concern is that children’s lifetime exposure to the energy
from cell phones will be greater than adults’, who started using them at a
later age.
Finally,
the measurement of cell phone use in most studies has been crude. Most have
been case-control studies, which have relied on people’s memories about their
past cell phone use. In these types of studies, it can be hard to interpret any
possible link between cancer and an exposure. People with cancer are often
looking for a possible reason for it, so they may sometimes (even
subconsciously) recall their phone usage differently than people without
cancer.
With
these limitations in mind, it is important that the possible risk of cell phone
exposure continue to be researched using strong study methods, especially with
regard to use by children and longer-term use.
What do expert agencies say?
Several
national and international agencies study different exposures and substances in
the environment to determine if they can cause cancer. (Something that causes
cancer or helps cancer grow is called a carcinogen.)
The American Cancer Society looks to these organizations to evaluate the risks
based on evidence from laboratory and human research studies.
Based
on the available evidence, some of these expert agencies have evaluated the
cancer-causing potential of cell phones and RF waves. In general, they agree
that the evidence of a possible link is limited, and more research is needed to
look at possible long-term effects.
The International Agency for
Research on Cancer (IARC) is part of the World Health Organization
(WHO). Its major goal is to identify causes of cancer. The IARC has classified
RF fields as “possibly carcinogenic to humans,” based on limited evidence of a
possible increase in risk for brain tumors among cell phone users, and
inadequate evidence for other types of cancer. (For more information on the
IARC classification system, see Known & Probable
Human Carcinogens.
The
other main agencies that classify cancer-causing exposures (carcinogens),
including the US Environmental Protection Agency (EPA) and the National
Toxicology Program (NTP), have not formally classified cell phones as to their
cancer-causing potential. However, several other agencies have commented on the
possible risks.
According
to the Food and Drug Administration (FDA), which regulates
the safety of radiation-emitting devices such as cell phones in the United States
“The
majority of studies published have failed to show an association between
exposure to radiofrequency from a cell phone and health problems.”
According to
the Federal Communications Commission (FCC):
“There
is no scientific evidence that proves that wireless phone usage can lead to
cancer or a variety of other problems, including headaches, dizziness or memory
loss. However, organizations in the United States
According
to the Centers for Disease Control and Prevention (CDC):
“At
this time we do not have the science to link health problems to cell phone use.
Scientific studies are underway to determine whether cell phone use may cause
health effects.”
According
to the National Institute of Environmental Health Sciences (NIEHS), which is conducting
studies of the possible health effects of cell phones:
“Current
scientific evidence has not conclusively linked cell phone use with any adverse
health problems, but more research is needed.”
According
to the National Cancer Institute (NCI):
“Studies
thus far have not shown a consistent link between cell phone use and cancers of
the brain, nerves, or other tissues of the head or neck. More research is
needed because cell phone technology and how people use cell phones have been
changing rapidly.”
Do cell phones cause any other health problems?
A
few other health concerns have been raised about cell phone use. One has been
whether the RF waves from cell phones might interfere with medical devices such
as heart pacemakers. According to the FDA, cell phones should not pose a major
risk for the vast majority of pacemaker wearers. Still, people with pacemakers
may want to take some simple precautions to help ensure that their cell phones
don’t cause a problem, such as not putting the phone in a shirt pocket close to
the pacemaker.
Several
studies have found that people who use cell phones while driving are more
likely to be in car accidents. It is not clear if hands-free phones are safer
than hand-held phones when it comes to driving.
Can I lower my exposure to RF waves from cell phones?
It
is not clear at this time that RF waves from cell phones cause harmful health
effects in people, but studies now being done should give a clearer picture of
the possible health effects in the future. Until then, there are several things
that people who are concerned about RF waves can do to limit their exposure.
Use the speaker mode on the phone or a hands-free device such as a
corded or cordless earpiece. This moves the antenna away from your
head, which decreases the amount of RF waves that reach the head. Corded
earpieces emit virtually no RF waves (although the phone itself still emits
small amounts of RF waves that can reach parts of the body if close enough,
such as on the waist or in a pocket). 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).
Texting instead of talking on the phone may be another option to
reduce your exposure.But it may not be a good option in
some situations, especially if you are driving. For safety reasons, it is
especially important to limit or avoid the use of cell phones while driving.
Limit your (and your children’s) cell phone use. This is one of
the most obvious ways to limit your exposure to RF waves from cell phones. You
may want to use your cell phone only for shorter conversations, or use it only
when a conventional phone is not available. Parents who are concerned about
their children’s exposure can limit how much time they spend on the phone.
Some people might consider choosing a phone with a low SAR value. Different
models of phones can give off different levels of RF waves. But as noted above,
according to the FCC the SAR value is not always a good indicator of a person’s
exposure to RF waves during normal cell phone use. One way to get information
on the SAR level for a specific phone model is to visit the phone maker’s
website. The FCC has links to some of these sites here: www.fcc.gov/encyclopedia/specific-absorption-rate-sar-cellular-telephones. If you know the
FCC identification (ID) number for a phone model (which can often be found
somewhere on the phone or in the user manual), you can also go to the following
web address: www.fcc.gov/oet/ea/fccid. On this page,
you will see instructions for entering the FCC ID number.
No comments:
Post a Comment