- Do electric and magnetic fields cause
leukemia in children? Despite government claims that evidence is weak,
a new study has added another wrinkle to the controversy.
- Researchers at the The Hospital for Sick
Children found that children with higher exposures to magnetic fields in
residences are two to four times more likely to develop leukemia than children
who received less exposure.
- "The risk for magnetic fields was
most significant in those who developed leukemia under the age of 6,"
said Mark Greenberg, professor of pediatrics at the University of Toronto
and pediatric oncologist at the Hospital for Sick Children in Toronto.
Results of the study appear in the July issue of two journals: the International
Journal of Cancer and Cancer Causes and Control.
- Researchers compared 201 children younger
than 14 living in the Toronto area who were diagnosed with leukemia between
1985 and 1993 at the Hospital for Sick Children with a control group of
406 healthy children. It is the first study to factor in the exposure to
electromagnetic fields (EMFs) over time.
- Some of the children in the Toronto study
wore monitors that measured their EMF exposure over a 48-hour period. Researchers
said the monitors produced more accurate data than past studies that measured
the amount of EMF at a single point in time.
- The researchers measured the EMF exposure
of children who did not wear the monitors by recording EMF levels inside
and outside their homes. They also examined the wiring in the children's
- Whether or not electric and magnetic
fields -- which emanate from outdoor electric lines as well as from lines
buried in the walls and from home appliances -- increase the risk of childhood
leukemia has been debated since the first study on the topic was presented
20 years ago.
- In July 1997, a study published in The
New England Journal of Medicine found no association between EMF exposure
and cancer, and these researchers said the issue could be put to rest.
But shortly thereafter, other studies were published associating an increased
risk of leukemia with EMF exposure.
- "Clearly, it's not put to rest because
studies like these keep coming out," said Michael Link, a professor
of pediatrics at Stanford University Medical School who is conducting his
own study of EMF exposure and leukemia.
- Link's study will not only measure EMF
exposure levels, but will also examine changes in children's leukemic cells
to try to come up with some physical evidence.
- If the same changes are found in EMF-exposed
children who have a certain type of leukemia, "it would imply that
there is some mechanism." Link said. "There's not very much evidence
that this low level of EMF has any biological effect on cells. If it made
things happen in blood cells, that would give some probability."
- Greenberg, the University of Toronto
pediatrician, agreed that no study to date has established that magnetic
fields cause cancer, because a biological process caused by EMF exposure
has not been identified.
- "What we are saying is this is an
association. We can't predict cause and effect, but we think it's important
statistical and epidemiological evidence," he said. "To transform
that into cause and effect you have to find a mechanism."
- "There are some very interesting
and provocative studies coming down the pike, but there's nothing conclusive
yet," Greenberg added.
- Both Greenberg and Link said the fact
that it is so difficult to measure EMFs is one likely reason for the discrepancy
- "It's hard to know that your results
will correlate with exactly what you're measuring," Link said.
- Last week, the National Institute of
Environmental Health Sciences (NIEHS) recommended to Congress that EMF
exposure be recognized as a "possible" cancer hazard.
- Its report said that after six years
of research and two years of review, researchers had concluded that EMF
exposure "cannot be recognized as entirely safe." Still, "The
NIEHS believes the probability that EMF exposure is truly a health hazard
is currently small. The weak epidemiological associations and lack of any
laboratory support for these associations provide only marginal scientific
support that exposure to this agent is causing any degree of harm."
- "Lingering concerns," the report
added, warrant additional studies and efforts to reduce EMF exposure should