Possible health risks >
EMFs and childhood cancer
Overview
Some recent important research results
Conclusions of review groups
See here for some basic facts
and figures on childhood cancer and leukaemia in particular.
Overview
The studies
Around 20 epidemiological studies have now been performed looking
just at a possible link between childhood leukaemia and EMFs. Scientific
papers have an abstract and you can read the abstracts of the
more important epidemiological studies here. Some of those studies
found no association with magnetic fields, but some have found associations.
Overall there is a statistical association within the studies that
have been performed between unusually high magnetic fields and childhood
leukaemia. By contrast, the evidence from the laboratory is that
low level EMFs of the type experienced by the public do not seem
to have the harmful effects that have been claimed.
Most studies have looked at whether EMFs cause childhood leukaemia
but one recent study has looked at
whether magnetic fields affect survival from leukaemia. One study has
looked at children with Down's syndrome rather than children in general.
What do the studies show?
Associations from epidemiological studies on their own do not establish
causation. The associations could be caused by two other things:
- Bias in the study. If the children chosen to take part in the
study were not properly representative of the population as a
whole, the association that was found in the study might not exist
in the rest of the population. We know that this problem (often
called “control selection bias”) exists in most of
the studies; what we don’t yet know is exactly how significant
it is. More on this.
- Other factors which were not properly controlled for. Something
which does actually cause childhood cancer might be associated
with magnetic fields so that children are exposed to both at once.
Then the association that the study found would be caused by the
other factor and not by EMFs. This is known as a “confounding
factor”. Click here
for a list of some of the other factors which vary with magnetic
fields.
More on what epidemiology can
or cannot show.
Evidence in summary
How many children may be affected?
The NRPB calculate that the raised risk for childhood leukaemia
suggested by epidemiological studies, if it were real, would correspond
roughly to an extra two cases of childhood leukaemia per year in
the UK, compared to an annual total of around 500 cases. More on
numbers of children and cases.
Some Recent Important Research Results
The Childhood Cancer Research Group
Study
This study (also known as the “Draper” study) is a collaboration
between the
CCRG at the
University of Oxford and National Grid. It looks at whether
children who get cancer were born near power lines or not. It found:
“While few children in England and Wales live close to
high voltage power lines at birth, there is a slight tendency
for the birth addresses of children with leukaemia to be closer
to these lines than those of matched controls.”
The strange thing about this result is that it seems to extend
much further from power lines – up to 600 m – than magnetic
fields do. The authors say:
“…our results do not seem to be compatible with the
existing data on the relation between magnetic fields and risk.”
and
“We have no satisfactory explanation for our results in
terms of causation by magnetic fields or association with other
factors.”
So this result suggests that if something is happening round power
lines it may not be the fields, it might be something else, perhaps
some characteristic of the areas power lines pass through.
more detail on this study including the complete abstract
‘Pooled’ analysis
In 2000, an international group, led by Professor Anders Ahlbom
from Sweden, took all the recent separate epidemiological studies
of childhood leukaemia and magnetic fields and pooled the results,
so that they could perform one single re-analysis of all the available
data. They found that, statistically, there was little or no suggestion
of an increased risk at the levels of magnetic fields to which the
overwhelming majority of children are exposed. The study did, however,
find that in the category of homes with a field, averaged over 24
hours, of greater than 0.4 microteslas
(which affects fewer than half a percent of children in the UK)
there is a statistical suggestion of increased risk. Some of these
homes are near power lines, but many are not. They concluded:
“The explanation for the elevated risk is unknown, but
selection bias may have accounted for some of the increase.”
Full abstract.
More on selection
In view of the importance of this study, we have reproduced the
main results table here.
see also a pooled analysis of night-time exposure
The United Kingdom Childhood Cancer Study
The biggest of all the epidemiological studies of EMFs and childhood
cancer was conducted during the 1990s, called the United Kingdom
Childhood Cancer Study (UKCCS). It looked at a number of suggested
causes of childhood cancer including EMFs. Its particularly large
study population – over 2000 cases of cancer in total, three
times larger than the next largest study before it – makes
it very powerful. It was conducted by an eminent group of scientists,
led by Sir Richard Doll, who first identified the link between smoking
and lung cancer.
The UKCCS was designed to look at every case of childhood leukaemia
occurring in the UK over roughly a four-year period. It is hard
to envisage a study better able to give comprehensive answers about
childhood cancer in the UK, and if a link with EMFs exists, this
study was expected to find it.
The study looked at three different aspects of EMFs:
First, in December 1999, the UKCCS published its report on exposure
to magnetic fields and concluded:
“This study provides no evidence that exposure to magnetic
fields associated with the electricity supply in the UK increases
risk for childhood leukaemia, cancers of the nervous system, or
any other childhood cancer.”
Next, in November 2000, the UKCCS looked at children living close
to power lines and concluded:
“There was no evidence that either proximity to electrical
installations or the magnetic field levels they produce in the UK
is associated with increased risk of childhood leukaemia or any
other cancer.”
Finally, in November 2002, the UKCCS published its report on electric
fields and concluded:
“In summary, this pilot study provides no support for the
hypothesis that residential exposure to EMF electric fields is associated
with childhood cancer…. Efforts to uncover the causes of childhood
malignancy appear better targeted in other directions.”
Conclusions of Review Groups
The view of the NRPB
In a major review of the evidence for a possible association between
exposure to power-frequency electric and magnetic fields and the
incidence of cancer published in March 2001, the NRPB Advisory Group
on Non-Ionising Radiation concluded:
“Laboratory experiments have provided no good evidence
that extremely low frequency electromagnetic fields are capable
of producing cancer, nor do human epidemiological studies suggest
that they cause cancer in general. There is, however, some epidemiological
evidence that prolonged exposure to higher levels of power frequency
magnetic fields is associated with a small risk of leukaemia in
children. In practice, such levels of exposure are seldom encountered
by the general public in the UK. In the absence of clear evidence
of a carcinogenic effect in adults, or of a plausible explanation
from experiments on animals or isolated cells, the epidemiological
evidence is currently not strong enough to justify a firm conclusion
that such fields cause leukaemia in children. Unless, however,
further research indicates that the finding is due to chance or
some currently unrecognised artefact, the possibility remains
that intense and prolonged exposures to magnetic fields can increase
the risk of leukaemia in children.”
In its new advice on exposure
limits in 2004, the NRPB stated:
“In the view of NRPB, the epidemiological evidence that
time-weighted average exposure to power frequency magnetic fields
above 0.4 µT is associated with a small absolute raised
risk of leukaemia in children is, at present, an observation for
which there is no sound scientific explanation. There is no clear
evidence of a carcinogenic effect of ELF EMFs in adults and no
plausible biological explanation of the association that can be
obtained from experiments with animals or from cellular and molecular
studies. Alternative explanations for this epidemiological association
are possible: for example, potential bias in the selection of
control children with whom leukaemia cases were in some studies
and chance variations resulting from small numbers of individuals
affected. Thus any judgements developed on the assumption that
the association is causal would be subject to a very high level
of uncertainty.”
More on NRPB.
The view of IARC
The International Agency for Research on Cancer (IARC) is an agency
of the World Health Organisation. Its Unit of Carcinogen Identification
and Evaluation has, since 1972, periodically published Monographs
which assess the evidence that various agents are carcinogenic and
classify the agents accordingly. In June 2001, a Working Group met
to consider static and extremely-low-frequency electric and magnetic
fields. The complete results have been published as Monograph number
80. Power-frequency magnetic fields were classified as “possibly
carcinogenic”, on the basis of “limited” evidence
from humans concerning childhood leukaemia, “inadequate”
evidence from humans concerning all other cancer types, and “inadequate”
evidence from animals. Power-frequency electric fields were judged
“not classifiable” on the basis of “inadequate”
evidence from both humans and animals. More
on IARC
The view of ICNIRP
A major review on epidemiology published by ICNIRP in 2001 concluded:
“Following the original report by Wertheimer and Leeper
linking the three most common forms of childhood cancer with a
proxy measure of residential EMF (wire codes), more than 18 studies
in nine countries have shown no convincing evidence of a relationship
between childhood leukaemia and residential EMF exposures among
children with estimated exposure levels under 0.2 µT. A
2-fold increase in relative risk of childhood leukaemia, confined
to a very tiny fraction of children (estimated as 0.8% in one
large pooled analysis) with residential EMF exposures ≥0.4
µT, is difficult to interpret in the absence of a known
biological mechanism or reproducible experimental support of carcinogenesis.
There is also some evidence to suggest that selection bias may
account for some of the increase in risk among the proportion
of children with high residential EMF exposure.” More
on ICNIRP
The view of WHO
The WHO Environmental Health Criteria Monograph
published in 2007 concluded:
"The IARC classification was heavily influenced by the associations observed in
epidemiological studies on childhood leukaemia. The classification of this
evidence as limited does not change with the addition of two childhood
leukaemia studies published after 2002. Since the publication of the IARC
monograph the evidence for other childhood cancers remains inadequate.
Overall conclusion
New human, animal and in vitro studies, published since the 2002 IARC monograph, do not change the
overall classification of ELF magnetic fields as a possible human carcinogen."
More on the WHO Monograph
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