-=PCTechTalk=- PSA on cell phones
- From: "Larry Southerland" <larrysoutherland@xxxxxxxxxxxxx>
- To: <the_bullhorn2@xxxxxxxxxxxxxxx>, <thebullhornsbest@xxxxxxxxxxxxxxx>, <Puters_N_Such@xxxxxxxxxxxxxxx>, <pctechtalk@xxxxxxxxxxxxx>
- Date: Tue, 31 May 2011 19:35:47 -0400
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http://scienceblog.cancerresearchuk.org/2011/05/31/who-verdict-on-mobile-pho
nes-and-cancer/
World
<http://scienceblog.cancerresearchuk.org/2011/05/31/who-verdict-on-mobile-ph
ones-and-cancer/> Health Organisation verdict on mobile phones and cancer
A smartphone
There's not enough evidence to say for sure
Do mobile phones cause cancer? The debate has been raging for years, and
we've covered it several
<http://scienceblog.cancerresearchuk.org/2010/06/23/no-link-between-childhoo
d-cancer-and-mobile-phone-base-stations-or-masts/> times on
<http://scienceblog.cancerresearchuk.org/2008/07/25/do-mobile-phones-cause-c
ancer/> this blog.
Today, the International Agency for Research into Cancer (IARC), which is
part of the World Health Organisation - had their say
<http://www.iarc.fr/en/media-centre/pr/2011/pdfs/pr208_E.pdf> . Over the
last week, they convened a panel of 31 experts to look at the available
evidence. Their verdict: "radiofrequency electromagnetic fields" - the sort
given off by mobile phones - belong to "Group 2B", which means that they
"possibly" cause cancer in humans.
What does that mean?
It means that there is some evidence linking mobile phones to cancer, but it
is too weak to make any strong conclusions. Specifically, IARC's panel said
that the evidence that mobile phones pose a health risk was "limited" for
two types of brain tumours - glioma
<http://www.cancerhelp.org.uk/type/brain-tumour/about/types-of-primary-brain
-tumours#glioma> and acoustic
<http://www.cancerhelp.org.uk/type/brain-tumour/about/types-of-primary-brain
-tumours#acoustic> neuroma - and "inadequate" when it comes to other types
of cancer.
The Chairman of the group, Dr Jonathan Samet, said, "The conclusion means
that there could be some risk, and therefore we need to keep a close watch
for a link between cell phones and cancer risk."
IARC classifies different things according to whether they are likely to
cause cancer, from tobacco to viruses to certain jobs. They are the gold
standard for this sort of thing. They have five possible categories of
risk:
Group 1 is the highest, reserved for things like smoking, asbestos, alcohol
and so on. It means that there's extremely strong evidence that the thing in
question causes cancer.
Group 2A includes things that are "probably carcinogenic to humans". Here,
the evidence is "limited" in humans, but "sufficient" from animal studies.
Group 2B - this is the one that mobile phones now fall under - means
something is "possibly carcinogenic to humans". It means there is "limited
evidence" that something causes cancer in people, and even the evidence from
animal studies is "less than sufficient". Group 2B means that there is some
evidence for a risk but it's not that convincing. This group ends up being a
bit of a catch-all category, and includes everything from carpentry to
chloroform.
Group 3 means that something is "not classifiable as to its carcinogencity
to humans". This means that the evidence is "inadequate in humans or
"inadequate or limited" in animals. Usually, there just haven't been enough
studies to say either way.
Group 4 means something probably doesn't cause cancer in humans. So far,
there is only one chemical - caprolactam
<http://en.wikipedia.org/wiki/Caprolactam> - in this group. People jokingly
take this to mean that everything causes cancer but it simply reflects the
fact that IARC focuses its attention on things that could potentially pose a
health risk.
Where does the evidence come from?
Even though this topic gets a lot of press attention, there have been a
relatively small number of studies on mobile phones and cancer. Most of
these are "case-control studies" - they compare people who already have
cancer (cases) with healthy people (controls), and ask them about how they
used their phones in the past. These studies include the InterPhone study,
<http://www.ncbi.nlm.nih.gov/pubmed/20483835> an international
collaboration of scientists from 13 countries, and work by Lennart Hardell's
group at University Hospital, Orebro.
So far, only one Danish study has actually followed a group of healthy
people (around 420,000 of them) to see if their use of mobile phones
affected their future risk of cancer.
What does the evidence say?
A smaller number of publications, mostly from the Hardell group, have found
associations between mobile phones and brain cancer risk. But the majority
of papers, including those from InterPhone
<http://www.ncbi.nlm.nih.gov/pubmed/20483835> and the Danish study
<http://www.ncbi.nlm.nih.gov/pubmed/17148772> , have found that mobile phone
use does not increase the risk <http://www.ncbi.nlm.nih.gov/pubmed/19593153>
of brain cancer, or any other type of cancer, for at least 10 years of use.
To give you an idea of the evidence to date, here are two images that
represent the studies on mobile phones and glioma brain cancers up to 2009
(taken from this paper <http://www.ncbi.nlm.nih.gov/pubmed/19593153> ). The
top one shows the effect of short-term use (less than 5 years), and the
bottom one deals with long-term use (more than 5 years). Each dot shows the
result from a single study. If it's on the horizontal line, there is no
effect. If it's above or below the line, this suggests that phones might
increase or reduce the risk of cancer respectively.
The bars above and below the dot are important - they represent the
"confidence interval", which indicates how reliable the result is. If the
bars cross the horizontal line, this means the result is not statistically
significant. It could have been down to chance, or bias. As you can see,
only one study out of 14 found the mobile phones significantly affect the
risk of cancer.
The dot that's second from the right (labelled "pooled estimate") represents
the combined results from all the studies. Again, you can see that it's
pretty much sitting on the line, which suggests that mobile phones do not
affect the risk of cancer.
<http://cancerresearchuk.files.wordpress.com/2011/05/mobile-phones.jpg>
click to enlarge
Some studies have suggested that people have a higher risk of brain cancer
specifically on the side of the head that they say they hold their phones
to. However, many of these studies have also reported either no overall
increased risk of cancer, or a lower risk of tumours on the other side of
the head.
Scientists disagree as to whether this "side-of-head effect
<http://www.ncbi.nlm.nih.gov/pubmed/19581357> " is real. If phones were
really increasing the risk of brain cancer on one side of the head, you
would still expect to see this reflected in the overall result.
Alternatively, the result could be due to bias, because people inaccurately
remembered how they used their phones (see below). Nor is it clear if people
actually hold their phones consistently to one side of their heads.
What are the weaknesses of these studies?
All the existing studies suffer from similar problems.
* Changing technology. Mobile phone technology has also changed
considerably over the last decades and it is not clear if studies based on
use of old models will apply to modern ones.
* Assessment problems. There still are no clear ways of assessing
someone's actual exposure to mobile phone radiation. Instead, studies use
questionnaires to work out whether and how people use mobile phones. These
questionnaires rely on people accurately remembering their past mobile phone
use years or decades ago. In some of the Hardell studies, a third of
patients received help from relatives in completing the questionnaires
(compared to just one in ten controls). In one case, the next-of-kin of
deceased <http://www.ncbi.nlm.nih.gov/pubmed/20551697> patients estimated
how often their loved ones used their phones.
* Recall bias. It's not clear if the replies to these questionnaires
are accurate - a problem known as "recall bias". Answers might be biased
because people have heard about mobiles and brain cancer in the media,
because brain cancer can distort memory, or simply because people
misremember things that happened a long time ago.
The individual studies have drawn more specific criticisms.
The Danish study relied on subscriber records instead of questionnaires.
However, there are concerns that subscribers aren't always the ones who use
the phones, and that this method excludes corporate users, who could use
their phones heavily.
For example, the InterPhone study has been criticized for using unrealistic
definition of "regular users" and having low response rates to its
questionnaires. The authors have also disagreed as to how their results
should be interpreted.
The Hardell group has
<http://www.hpa.org.uk/web/HPAweb&HPAwebStandard/HPAweb_C/1254510602951>
been criticised for publishing the same data in multiple papers,
inconsistently reporting data such as sample sizes, and having implausibly
high response rates to its questionnaires.
The abstracts of their papers often highlight statistically significant
links in very specific groups of
<http://www.ncbi.nlm.nih.gov/pubmed/17409179> people, while ignoring
overall negative results. These types of analyses are difficult to interpret
- if you split a sample far enough, you end up with small numbers of people
in each group and greater odds of finding a positive result simply through
chance.
Are there conflicts of interest?
The mobile phone industry has provided funding for the InterPhone study and
the Danish study. In both cases, funds have been administered through
independent, third-party organisations that are meant to act as "firewalls"
to ensure the independence of the scientists. InterPhone, for example,
received 19.2 million euros of funding. 5.5 million of this total came from
industry sources, and was either administered through the International
<http://www.uicc.org/> Union for Cancer Control, or collected via taxes and
fees from government agencies.
Lennart Hardell has not received funding from industry sources but has
appeared as an expert witness in
<http://www.sciencemag.org/content/298/5592/338.full> litigation cases
involving mobile phones.
Could mobile phones cause cancer?
This is an important question. Scientists are confident that tobacco,
alcohol or asbestos can cause cancer because they can explain how these
things affect the way our cells work. These explanations are called
"biological mechanisms" - they play a vital role in establishing that
something causes cancer.
So far no one has been able to provide a good biological mechanism for the
link between mobile phones and cancer. The "how" question is an open one.
The phones give off microwave radiation, but this has millions of times less
energy than, say, an X-ray and is not powerful enough to damage our DNA.
They mildly heat the body, but again, not enough to pose a health risk.
Other suggestions have been put forward, but none are backed by consistent
evidence.
Are brain cancer rates going up?
If mobile phones increase the risk of brain cancer, the rates of this
disease should be skyrocketing since mobile phone use has risen dramatically
over the last few decades.
But studies in the US <http://www.ncbi.nlm.nih.gov/pubmed/20639214> , New
Zealand <http://www.ncbi.nlm.nih.gov/pubmed/12838353> , Denmark, Norway,
Sweden and <http://www.ncbi.nlm.nih.gov/pubmed/19959779> Finland have found
no such trends. In the UK, the incidence of brain cancer has
<http://info.cancerresearchuk.org/cancerstats/types/brain/incidence/#trends>
been flat for the past few decades. A recent English study
<http://www.ncbi.nlm.nih.gov/pubmed/21280060> concluded that "the increased
use of mobile phones between 1985 and 2003 has not led to a noticeable
change in the incidence of brain cancer in England between 1998 and 2007."
Brain cancers can take many years to develop, so it is possible that trends
would only start rising after more time.
What about base stations?
Base station exposures are much less likely to affect our health than phones
themselves as their emissions are many times weaker and usually well below
international guidelines.
Just last year, a
<http://scienceblog.cancerresearchuk.org/2010/06/23/no-link-between-childhoo
d-cancer-and-mobile-phone-base-stations-or-masts/> British study (the
largest of its kind) found "no association between risk of childhoodcancers
and mobile phone base station exposures during pregnancy".The authors say
the results "should help to place any future reportsof cancer clusters near
mobile phone base stations in a widerpublic health context."
What should we make of the evidence?
It is understandable that people are concerned about mobile phones,
especially because they are so widely used. But so far, the published
studies do not show that mobile phones could increase the risk of cancer.
This conclusion is backed up by the lack of a solid biological mechanism,
and the fact that brain cancer rates are not going up significantly.
However, all of the studies so far have weaknesses, which make it impossible
to entirely rule out a risk. Mobile phones are still a new technology and
there is little evidence about effects of long-term use.
For this reason, the UK Government advises a precautionary stance. It
suggests that if adults want to use a mobile phone, they can choose to
minimise their exposure by keeping calls short. It also advises discouraging
children under the age of 16 from making non-essential calls as well as also
keeping their calls short.
And, as IARC's working group said, there needs to be more research.
What studies are in the pipeline?
A large study called COSMOS <http://www.ukcosmos.org/> , including
researchers from the UK and four other countries, has been set up to look at
the long-term effects of mobile phone use after 20-30 years. Like the
Danish study, it will recruit healthy people, measure their mobile phone use
and see if this affects their health in the long-term.
The MOBI-KIDS <http://mbkds.com/> study, involving 13 countries, has been
set up to look at health effects in childre
Your friend,
Larry
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