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发帖数: 9638 | 20 Recommendations on Cell Phone Use and Cancer Risk（ZZ)
Allison Gandey
Information from Industry
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For office-based physician not adopting an electronic health records(EHR)
system by 2015, Medicare payments are planned to be reduced.
Calculate impact June 22, 2011 — The evidence is limited when it comes to
cell phones and cancer risk, but specialists say common-sense measures can
come into play until the science catches up with technology.
The issue is back in the news after the World Health Organization's (WHO's)
recent announcement that cell phone use should be considered "possibly
carcinogenic." There are an estimated 5 billion mobile phones in use around
the world.
The working group from the organization's International Agency for Research
on Cancer (IARC) was careful not to make any firm conclusions.
A hands-free device places more distance between the mobile phone and the
brain.
"The evidence, while still accumulating, is strong enough to support a
conclusion and the 2B classification," reported Working Group Chair Jonathan
Samet, MD, from the University of Southern California in Los Angeles. This
category is used for agents when there is limited evidence.
Others have suggested a cancer risk before, but the organization's
consortium is the most significant to classify the radiation emitted by cell
phones in this way.
Still, the group, which consists of 31 scientists from 14 countries, avoided
calling cell phones carcinogenic and passed on classifying them even as
probably cancer causing.
This has left some practicing clinicians shaking their heads in annoyance as
cancer fears ripple through the community.
"The classification the working group selected is very weak, and I think
people are now focusing too much on the possibly carcinogenic part," neuro-
oncologist Lynne Taylor, MD, from Virginia Mason Medical Center in Seattle,
Washington, said in an interview.
Dr. Taylor says she agrees that more research is necessary, but this won't
affect how she uses her cell phone or counsels patients. "This is not
anything to worry about," she said.
"I think that any problems reflect the subtlety of 'possible,' which by no
means indicates an established carcinogen," Dr. Samet told Medscape Medical
News. Despite some misunderstanding, he added, "many have interpreted the
statement correctly."
However, Dr. Samet acknowledged, "anyone concerned about risk can take steps
to reduce exposure by using a hands-free device or texting. Additionally,
current phones have lower outputs than the older phones that were
investigated in the epidemiological studies."
The Lancet Oncology published the WHO's full working group report online
June 22. Interestingly, it appears that not all members of the IARC working
group were completely in agreement either on how to view the risk for cancer
from cell phone use.
Their conclusions were based on several studies, the published report notes.
Results of the INTERPHONE study published in 2010 showed that overall those
having ever used a cell phone appeared to be at a slightly lower risk of
developing glioma than never users. However, when the researchers considered
the top 10% of cell phone users, those with a total exposure of 1640 hours
or more, there was a 40% increase in risk vs never users. There was also
some indication of increased risk for ipsilateral exposure and for tumors in
the temporal lobe where radiofrequency exposure was highest.
The working group also reviewed a combined analysis of Swedish studies
showing participants who'd used a cell phone for more than a year had a 30%
increase in glioma risk vs never users. The risk increased with increasing
time since first use and with total call time, reaching a hazard ratio of 3.
2 for greater than 2000 hours of use; ipsilateral use was also associated
with higher risk.
"Although both the INTERPHONE study and the Swedish pooled analysis are
susceptible to bias — due to recall error and selection for participation
— the working group concluded that the findings could not be dismissed as
reflecting bias alone and that a causal interpretation between mobile phone
RF-EMF [radiofrequency electromagnetic field] exposure and glioma is
possible."
However, a Danish study that analyzed cancer rates and subscriptions for
cell phones from 1982 and 1995 showed no increased risk for glioma or other
brain cancers among users of cell phones. A number of earlier and smaller
case-control studies had also shown no connection, the study authors note.
Given these divergent findings, not all members of the group agreed on how
to interpret the overall evidence, the study authors acknowledge. "A few
members of the working group considered the evidence in humans 'inadequate,'
" the final report notes. "In their opinion, there was inconsistency between
the 2 case-control studies and a lack of exposure-response relationship in
the INTERPHONE study results; no increase in rates of glioma or acoustic
neuroma was seen in the Danish cohort study, and up to now, reported time
trends in incidence rates of glioma have not shown a parallel to temporal
trends in mobile phone use."
Still, they conclude that given the limited evidence in humans and
experimental animals, RF-EMF should be classified as "possibly carcinogenic
to humans" with a Group 2B classification. "The evaluation was supported by
a large majority of working group members," the study authors note.
Cancer Agencies Respond
After initial announcement of the WHO report, several major agencies moved
quickly to respond to these new conclusions that have been widely reported
in the consumer press. In a statement, the National Cancer Institute pointed
out, "This is neither new research nor at odds with previous findings."
The institute acknowledged it agrees with the working group that continued
monitoring of both brain cancer trends and new evidence from studies is
called for.
However, they point out that INTERPHONE, "considered the major study on cell
phone use and cancer risk, has reported that overall, cell phone users have
no increased risk of the most common forms of brain tumors — glioma and
meningioma." The study showed no increased risk associated with
progressively increasing number of calls, longer call time, or years since
beginning cell phone use, the statement notes. "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 National Toxicology Program at the National Institute of Environmental
Health Sciences is currently leading the largest laboratory rodent study to
date on cell phone radiofrequency exposures and potential health hazards,
the institute statement adds. "The studies are designed to mimic human
exposure and are based on the frequencies and modulations currently in use
in the United States."
The bottom line is the evidence is enough to warrant concern, but it is not
conclusive.
The American Cancer Society has also weighed in. "This report comes from a
very credible group and reaches reasonable conclusions about electromagnetic
radiation from cell phones and other devices," Chief Medical Officer Otis
Brawley, MD, said in a statement.
"It is critical that its findings be interpreted with great care," he
cautions. "The working group reviewed a large number of studies and
concluded that there was limited evidence that cell phones may cause glioma.
" The bottom line, Dr. Brawley said, "is the evidence is enough to warrant
concern, but it is not conclusive."
Radiofrequency Exposure
The fear is that radiofrequency electromagnetic fields produced by cell
phones may affect the brain and other tissues because handheld devices are
usually held close to the head. Researchers are looking at whether
radiofrequency energy can cause malignant brain tumors, such as gliomas, as
well as benign tumors, including acoustic neuromas and meningiomas. The WHO
report notes that third-generation (3G) mobile phones emit about 100 times
less radiofrequency energy than global system for mobile communications (GSM
) handsets, when signals are strong. They also highlight that the average
output power of Bluetooth wireless hands-free kits is estimated to be around
100 times lower than that of mobile phones.
The current concern does not extend to cordless phones. Commonly used in
homes, these devices have base units that are plugged into phone jacks that
are wired to a local telephone service and operate at about 1/600 the power
of cell phones.
The US Food and Drug Administration and the Federal Communications
Commission have not linked cell phone use to cancer risk but have long
recommended steps that cell phone users can take if they are concerned:
•Reserve cell phone use for shorter conversations or for times when a
land line is not available; and
•Use a hands-free device that will place more distance between the
mobile phone and the brain.
A cell phone user's level of exposure to radiofrequency 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,
and, for older phones, how far the antenna is extended.
In a recent study published in the Journal of the American Medical
Association, investigators found that using a cell phone for as little as 50
minutes at a time appears to affect brain glucose metabolism in the region
closest to the phone's antenna.
The researchers used positron emission tomography during cell phone use in
the on and then off positions and found that although whole-brain metabolism
was not affected, metabolism was increased in the orbitofrontal cortex and
the temporal pole areas of the brain while the cell phone was on — areas
close to where the phone's antenna meets the head.
However, the researchers, with lead author Nora Volkow, MD, from the
National Institute on Drug Abuse in Bethesda, Maryland, acknowledge that it'
s not clear at this point whether this increase in metabolism is a good or
bad thing. Increasing glucose metabolism could potentially have a positive
effect in certain therapeutic situations.
Still, like Dr. Samet, Dr. Volkow recommends that cell phone users wanting
to play it safe consider hands-free devices or speaker-phone mode to avoid
direct contact of the cell phone with the head.
Worse for Children?
According to the National Cancer Institute and the American Cancer Society,
there are currently no data on cell phone use and cancer risk in children.
Even though cell phone use by children and adolescents is rising rapidly, no
published studies to date have included young people.
Children may be at greater risk because their nervous systems are still
developing. A large case-control study of childhood brain cancer in several
Northern European countries is now under way.
Researchers from the Centre for Research in Environmental Epidemiology in
Spain are conducting an international study known as Mobi-Kids to evaluate
risk from new communications technologies and other environmental factors in
young people ages 10 to 24 years.
There is no consensus among physicians and scientists about the severity of
risk, or even if one exists. One of the many hurdles in evaluating a
potential connection between cancer and cell phone use is the relatively
short period these devices have been heavily used in a large population and
the long latency period for many tumors.
Most teenagers are texting, and that's probably the most appropriate use for
mobile phones.
Dr. Taylor says that for younger patients taking precautions makes sense. "
Most teenagers are texting, and that's probably the most appropriate use for
mobile phones. It's the people from my generation who are more likely to be
pressing their cells against their ears. With teens, the focus of my
attention will be to remind them not to text and drive or use their cell
phone at all in the car."
She adds it probably isn't appropriate for very small children to be using
cell phones anyway. "So that solves that."
While the evidence remains uncertain, Dr. Brawley added, it is up to each
individual to determine what changes they wish to make after weighing the
potential benefits and risks of using a cell phone.
"Limiting use among children also seems reasonable in light of this
uncertainty. On the other hand, if someone is of the opinion that the
absence of strong scientific evidence on the harms of cell phone use is
reassuring, they may take different actions, and it would be hard to
criticize |
