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Can magnetic fields from power lines, computers and even common household appliances lead to health problems down the road?

A new study suggests that pregnant women with the highest levels of exposure to magnetic fields are more likely to have a child who develops asthma, compared to pregnant women with low exposure levels.

The study was conducted by the same researcher who made waves in 2002 with a study that suggested magnetic fields could boost a woman's chances of miscarriage.

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But many experts aren't convinced the risks are real and the medical field remains sharply divided over the presence of a link between health problems and exposure to electromagnetic fields.

Magnetic and electric fields are areas of energy around electrical devices and, in combination, are referred to as electromagnetic fields. Previous research has suggested EMFs may be linked to some types of cancer and other health problems, such asmiscarriages, poor semen quality and immune disorders.

EMFs emitted by power lines and home appliances, such asmicrowave ovens, hairdryers and vacuum cleaners, are referred to as "extremely low frequency" and should not be confused with devices such as cellphones, which emit higher-frequency EMFs called radiofrequency.

The potential health effects of radiofrequency fields are typically a source of greater concern among medical experts, particularly for cellphones and brain cancer.

But De-Kun Li, lead author of the new study published Monday by the Archives of Pediatrics and Adolescent Medicine journal, and a reproductive and perinatal epidemiologist at the Kaiser Permanente Division of Research in Oakland, Calif., says he believes magnetic fields are being overlooked as a potentially serious risk to health.

In his new study, Dr. Li and colleagues tracked pregnant women and their offspring for up to 13 years to assess the possible effects of magnetic fields on health.

Women involved in the study wore a small meter during pregnancy to measure their daily exposure to magnetic fields, which are emitted by microwaves, vacuum cleaners, fluorescent lights and power lines. The meters were equipped to measure only magnetic-field exposure, not electric-field exposure.

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Researchers tracked, for a maximum of 13 years, 626 children who were subsequently born to the women wearing the meters. Of those children, 130, or about 20 per cent, were clinically diagnosed with asthma.

They found women exposed to the highest levels of exposure to magnetic fields had a 3.5-fold increased risk of having a child who would later be diagnosed with asthma, compared to women with lower exposure levels.

The researchers also found women who had asthma or who were pregnant with their first child, two known risk factors for asthma in offspring, were more likely to have a child with asthma if they also had high levels of magnetic-field exposure. Dr. Li says this confirms the idea that magnetic fields can potentially lead to asthma in offspring.

"The message is EMF is bad," Dr. Li said. "You should avoid EMF as much as you can, especially during pregnancy."

Many health officials and medical experts, however, say people don't have much to worry about when it comes to magnetic fields, which use extremely low frequencies.

Health Canada says: "There is no conclusive evidence of any harm caused by exposures at levels found in Canadian homes and schools, including those located just outside the boundaries of power-line corridors."

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In 2002, the World Health Organization's International Agency for Research on Cancer classified extremely low-frequency magnetic fields as "possibly carcinogenic," a category shared by other possible risks, such as gasoline exhaust and occupational exposure to dry cleaning. The IARC said there is limited evidence that low levels of exposure to magnetic fields have a detrimental impact on health.

Another possibility is that high magnetic-field exposure may not be to blame in the asthma study, and other factors could be at play.

Warren Foster, a professor in the Department of Obstetrics and Gynecology at McMaster University in Hamilton, said a person who believes magnetic fields are a concern may be more likely to see them as the cause of certain health problems.

"Perception is really important. It really influences how you look at things," he said.

Dr. Foster added that women likely don't need to be alarmed about health risks from EMFs in their homes.

"I would have to say that this is something that is very low on the radar."

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Yet, because EMFs remain a relatively new reality in homes around the world, scientists haven't closed the book on the matter. The medical community is divided over the issue of whether cellphones, which use high-frequency radio waves, may cause cancer.

Dr. Li said it's all too easy for scientists to brush off concerns over low-frequency magnetic fields, but that his research demonstrates they could pose a real risk.

"There's a lot of people with dismissive attitudes," he said. "EMF is something you can't touch, can't see. …This really needs to [be paid] attention to."

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