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Strong magnetic fields produced by trains,
electric household appliances such as vacuum cleaners and
food mixers and vehicles increase the risk of miscarriage
by up to three times claim researchers in California.
Their findings also suggest that most
previous investigations into the health effects of electromagnetic
fields (EMFs) have been measuring the wrong thing.
One study was led by De-Kun Li, a reproductive
epidemiologist at the Kaiser Foundation Research Institute
in Oakland, California. His team asked 1063 women around San
Francisco who were in the first 10 weeks of pregnancy to spend
a day wearing a meter around their waists that measured magnetic
field levels every 10 seconds.
Overall, they found that women exposed
to peak levels of 1.6 microteslas or greater were nearly twice
as likely to miscarry as women not exposed to such strong
fields.
More significantly, says Li, among the
622 women who said the measuring period had been a typical
day, those who experienced high peak fields were three
times as likely to have a miscarriage. "That's
another confirmation that the effect is due to EMF,"
says Li.
Shavers and Hairdryers
Other factors can have a more dramatic
effect, however. The risk of a miscarriage increases tenfold
as women age, for example, from 5 per cent for women under
30 years old to 50 per cent for those in their mid-40s.
Li's team didn't look at what was producing
the fields, but appliances such as shavers,
hairdryers and vacuum cleaners can produce strong alternating
magnetic fields, as can electric vehicles such
as trams and trains. The key is proximity to the source, as
fields drop off rapidly with distance.
The team did not examine which appliances
were producing the strong fields, but devices with powerful
motors are known to be the worst culprits. Vacuum cleaners
and drills emit around 20 microteslas - more than 12 times
higher than the critical level in the study. Food mixers give
off around 10
Alternating magnetic fields also have
associated electric fields. The few previous studies of the
effect of low-frequency EMFs on miscarriages, such as one
involving 727 women done in 1991 by Raymond Neutra's group
at the California Department of Health Services in Oakland,
have been inconclusive.
But Li thinks this is because Neutra looked
at people's average exposure to electromagnetic fields over
time, not peak values. "People
have never looked at peak EMFs before," Li
says. "My study opens a new chapter for these EMF effects.
Not just for miscarriages, but for other health effects."
EMF Spikes
When Neutra reanalysed the data from his
earlier study, which has only now been published, he discovered
the results were similar to Li's. Women exposed to peak EMF
levels greater than 1.4 microteslas were nearly twice
as likely to miscarry.
Localized Heating
In the past, EMFs have been blamed for
various other ill effects, especially leukemia in children.
But no one can explain how relatively weak fields might cause
the DNA mutations that lead to cancer, and most studies have
failed to find evidence of a link.
The peak values measured by Li are way
below the recommended exposure limit of 1600 microteslas.
Above this level, EMFs can induce electric currents in the
body, which leads to localized heating.
Li speculates that EMF spikes could cause
miscarriages by subtly disrupting cell-to-cell communication.
"But as epidemiologists, we should not feel weaker because
we don't understand the mechanisms."
Epidemiology
January 2002 13:9-20
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