Children whose mothers had high exposure to microwave ovens, hair dryers and vacuum cleaners while pregnant may have three times the risk of developing asthma, U.S. researchers said on Monday in a study that adds to an ongoing debate.
While previous asthma studies have failed to consistently show that chronic exposure to electromagnetic fields is harmful to human health, researchers - such as Dr. De-Kun Li, senior research scientist at the Kaiser Permanente in Oakland, California - have argued that those tests were flawed -- being that they relied on the individuals to estimate their own exposure levels over a period of several years.
To eliminate the guesswork, Li designed a so-called prospective study in which 801 pregnant women wore monitors that accurately measured their exposure to magnetic fields for 24 hours.
During Li's study, the monitor did not pick up fields created by mobile phones and mobile phone masts, since those devices use a much higher frequency at the other end of the electromagnetic spectrum.
Armed with the EMF exposure numbers researchers then used electronic medical records to track their children for 13 years - in an effort see which of them developed asthma - and compared the results.
The study found that women with high EMF exposure in pregnancy had a more than threefold risk of asthma in their offspring compared with mothers whose exposure level was low.
"The message here is exposure to electromagnetic fields is not good, and we need to pay attention to its adverse effect on health," said De-Kun Li. "The best way to reduce your magnetic field exposure is distance. Magnetic field strength drops dramatically with increasing distance from the source."The Asthma-Magnetic Field study has been published online in the Archives of Pediatrics and Adolescent Medicine.