Electric and magnetic fields are everywhere. They’re generated by thunderstorms, microwave ovens, power lines, and even hybrid cars. Scientists for years have examined their impact on human health, but results have been conflicting.
In today’s Archives of Pediatrics & Adolescent Medicine, researchers present the first study to show an association between maternal exposure to magnetic fields (MF) during pregnancy and an increased risk of asthma in their offspring. The study included 801 pregnant women whose children were followed up for 13 years. To measure their MF exposures, the women wore 24-hour meters.
The researchers found that for each 1-milligauss (mG) increase in exposure per day, children had a significant 15% increased risk of asthma. What’s more, children born to women with the highest MF exposures during their pregnancy had a 3.5-fold increased risk of asthma compared with children whose mothers had the lowest exposures. (As a point of reference, other studies have linked increased cancer rates with workday exposures above 4 mG.)
The study could have important implications for asthma prevention. The condition affects more than 9 million children in the United States, and it carries a $30 billion annual price tag. news@JAMA spoke with lead author De-Kun Li, MD, PhD, a reproductive and perinatal epidemiologist at the Kaiser Permanente Division of Research in Oakland, Calif, to learn more about the findings.
news@JAMA: Were you able to determine the most common sources of MF exposures among women in the study?
Dr Li: For our population, we’re talking about low frequencies generated by electricity, like from power lines, microwave appliances, hair dryers, an electric toaster, or can opener—anything you plug in that has motors—and even fluorescent lights. We didn’t pick out each of the sources, but we did ask about their locations in 5 categories: at home in bed, at home but not in bed, at work, during transit, and all others. We found out that they get to the high level of exposure, greater than 2.0 mG, in each of those categories except in transit. For most people the average [daily] exposure is between 0.3 mG and 2.0 mG. You could have a high 50 mG exposure, but those are short brief bursts. Most times, you usually have constant low exposure levels.
news@JAMA: You also found that the more exposure a woman had, the greater her child’s risk of asthma. Did this dose-dependent relationship surprise you?
Dr Li: That did surprise me a little bit. Sometimes in science you know there might be something going on, but it’s hard to prove it. So I was surprised by how strong [the relationship] is. I think the reason why we find a nice dose-response relationship is because MF is really bad, particularly during pregnancy. The fetus is so sensitive in fetal development that any environmental adverse effect is going to be amplified.
news@JAMA: What implications for asthma prevention do your findings suggest?
Dr Li: Pregnant women really need to avoid MF exposure as much as they can. For asthma, particularly if your mother had asthma and if this is your firstborn baby, you should pay more attention. Our [data] show that if your mother had a history of asthma, MF exposure is particularly bad for you, and if this is your firstborn, MF exposure is particularly bad for you. There is no downside of avoiding MF.
news@JAMA. What are the implications for future research?
Dr Li: This is the first study to show that exposure to MF during pregnancy had a detrimental effect on the offspring. Hopefully, this opens up a new chapter of studying health effects and also hopefully we’ll cut through the thickness of dismissive attitudes out there about MF studies. Everybody is exposed, so if MF truly has adverse effects, it’s going to impact huge numbers in the population.