Possible association between maternal exposure to magnetic fields and development of asthma in children

Children whose mothers had high exposure to magnetic fields (MF) during pregnancy appear to have an increased risk of developing asthma, according to a new study.

According to the article, asthma is a common condition in children, affecting 13 percent of the U.S. population younger than 18 years, and having health and economic consequences. The authors note that asthma prevalence increased roughly 74 percent from 1980 to 1996 and that research on the potential risk of environmental physical exposures has been limited. Citing an increase in artificial electromagnetic fields (EMFs) from power lines, appliances, wireless networks and wireless devices, and other research possibly connecting EMFs to adverse health outcomes, they write, "This parallel increase in both EMF exposure and asthma prevalence in the past several decades warrants examination."

De-Kun Li, M.D., Ph.D., and colleagues from Kaiser Permanente, Oakland, Calif., conducted a prospective cohort study to examine the association between maternal exposure to high levels of MFs during pregnancy and risk of asthma in offspring. From 1996 to 1998, the authors recruited pregnant women who were members of Kaiser Permanente Northern California in the San Francisco area. Participants wore a meter that measured their MF levels for 24 hours, and then rated whether their activities during that period were typical. Offspring were followed until they received a diagnosis of asthma, they left the health system's care or the study period ended in August 2010.

During the 13 years of follow-up, 130 children (20.8 percent of the study participants) developed asthma, with most cases diagnosed by 5 years of age. Researchers observed a statistically significant linear dose-response relationship between increasing maternal median daily MF exposure level during pregnancy and an increased risk of asthma in children. Every one-milligauss increase in a pregnant woman's median MF exposure was associated with a 15 percent increase in the risk of the child developing asthma. The association was especially strong for firstborn children and those whose mothers had a history of asthma, two known risk factors for the condition.

"In conclusion, the findings of the present study open up a new area in understanding the risk factors for asthma and the health effects of ubiquitous MF exposure, especially during pregnancy," the authors state. "As with any epidemiological study, these findings need to be replicated. If confirmed, they have the potential to inform new intervention strategies to reduce asthma, the most prevalent chronic disease among children."