EMF scare returns: Maternal appliance use and asthma in offspring?

We were right that air pollution wasn’t causing asthma in kids; it’s actually hair dryers, vacuums and microwaves — or at least that’s what’s being claimed in a new study. “Women with high exposure to magnetic fields during pregnancy may have a higher risk of asthma in their children,” according to the media release for the new study from Kaiser Permanente researchers.

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Although the study is a first-of-its-kind, the researchers pretty quickly jettisoned the word “may”: While the replication of the finding is needed, the message here is exposure to electromagnetic fields is not good, said study lead author De-Kun Li, MD, PhD, a reproductive and perinatal epidemiologist at the Kaiser Permanente Division of Research in Oakland, Calif. Here’s the description of the study:

In this prospective study, researchers compared the daily magnetic field exposure of 801 pregnant women in Kaiser Permanente Northern California and used electronic medical records to follow their children for 13 years to see which children developed asthma. The study found that women with high MF exposure in pregnancy had a more than threefold risk of asthma in their offspring compared with mothers whose exposure level was low.

The researchers attempt to justify their result by noting:

The prevalence of asthma has been steadily rising since the 1980s, making it the most common chronic condition among children… EMF exposure is ubiquitous. Because of the widespread exposure, any adverse health effect of EMF could impact many people and cause a serious public health problem…”

But the researchers might have a better argument if they could show that asthma prevalence has been increasing since the 1880s when widespread electrification began. Past that, the study was designed to look for an association between EMF exposure and and miscarriage, not EMF and asthma. The asthma finding is there fore mostly likely to be an artifact of the study design — one most likely found through the multiple comparisons fallacy (i.e., if you look for enough associations, one or more will occur simply by chance). Also, since the study was not designed for the asthma outcome, insufficient data were collected to rule out confounding risk factors. Maternal exposure to EMF was based on a single 24-hour measurement during the first or second trimester. Then there’s the up to 13-year time lag between exposure and diagnosis. Let’s not forget that there is no plausible biological explanation for how EMF could cause asthma. This study is comforting in that it is as junky as the 1990s-era studies that killed the EMF scare in the first place.