"The studies really represent state-of-the-art research into the causes of pregnancy loss," says epidemiologist David Savitz of the University of North Carolina in Chapel Hill. Nevertheless, he says the researchers' interpretation of their findings may be wrong. California is already initiating public hearings to discuss the findings.
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.
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.
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."
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.
But Savitz sees things differently. "Both studies found a reassuring lack of association for the most well-established measures of magnetic field exposure, that is average magnetic fields." The correlation between exposures to EMF spikes and an increased miscarriage rate may be due to other factors, he says. For instance, women who have a healthy pregnancy are more likely to suffer from nausea. This may make them more likely to stay at home and do less, and thus also reduce their exposure to magnetic fields.
After Savitz's comments, Li's team looked at their data again. They also checked for other possible risk factors such as drug use, carrying heavy loads and previous induced abortions. "We adjusted for 30 different kinds of risk factors. Nothing changed," says Li.
But Michael Bracken, an epidemiologist at Yale University, is unconvinced. "There are numerous ways of measuring these fields, and one worries that if you do it enough times, then you are going to find positive associations," he says. "There's a real risk in these things getting over-interpreted and scaring the dickens out of people."
In the past, EMFs have been blamed for various other ill effects, especially leukaemia 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 localised 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."
Author: Anil Ananthaswamy, San Francisco
More at: Epidemiology (vol 13, p 1, 9 and 21)
New Scientist issue: 12th January 2002
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