The present study is based on the prospective cohort study that was conducted to examine the effect of exposure to electromagnetic fields on the risk of miscarriage among pregnant members of the insurance company "Kaiser Permanente Northern California" who were recruited from 1996 to 1998 (Li et al 2002). After birth the children were followed up until the age of 13 to collect information on growth patterns with 33 weight measurements per child on average. Body mass index (BMI) was calculated if both weight and height were measured on the same day. Body weight was the primary measure for overweight/obesity. The "2000 Centers for Disease Control and Prevention (CDC) growth charts" for the USA were used to determine age-specific percentile in weight, the 97.5th percentile was defined as the cutoff for obesity.
|Reference group 1||maternal exposure to magnetic fields, 24 h-measurement, < 90th percentile: ≤ 0.15 µT|
|Group 2||maternal exposure to magnetic fields, 24 h-measurement, 90th percentile: > 0.15 µT|
|Group 3||maternal exposure to magnetic fields, 24 h-measurement: > 0.15 - 0.25 µT|
|Group 4||maternal exposure to magnetic fields, 24 h-measurement: > 0.25 µT|
Prenatal exposure to magnetic field level (> 0.15 µT) was associated with increased risk of being obese in offspring compared with a lower magnetic field level below 0.15 µT (OR 1.7, CI 1.01-2.84). Similar, but non-significant results were observed in children with calculated BMI. The association between prenatal exposure and obesity demonstrated a dose-response relationship and was stronger among children who were followed up to the end of the study. The association existed only for persistent obesity, but not for transitory obesity.
The authors conclude that maternal exposure to high magnetic fields during pregnancy might be a new and previously unknown factor contributing to the world-wide epidemic of childhood obesity and overweight.