Maternal exposure to magnetic field (MF) nonionizing radiation during pregnancy may increase offspring risk for attention-deficit/hyperactivity disorder (ADHD), according to findings from a birth cohort study published in JAMA Network Open. Many studies have previously focused on environmental exposures such as chemicals. However, MF nonionizing radiation, a common exposure given its source in electric appliances, power lines, and wireless network infrastructure, could be another key risk factor.
Investigators at Kaiser Permanente Northern California (KPNC) in Oakland, California designed a birth cohort study of mother-child pairs with available radiation exposure data. Radiation exposure levels were ascertained from 2 prior cohort studies conducted by KPNC from 1996 to 1998 and 2006 to 2012. In each study, pregnant women were assigned to wear an EMDEX meter for 24 hours to assess radiation levels encountered during daily life. The investigators also conducted a clinical interview to capture any confounding factors, and offspring were followed from 1997 to 2017 through the KPNC healthcare delivery system.
The primary outcome was physician-diagnosed ADHD. Investigators also captured the co-occurrence of immune-related comorbidities with ADHD, including asthma and atopic dermatitis (AD). Cox proportional hazards models were used to assess the differential risk for ADHD among the offspring of mothers with high vs low radiation exposure. Participants with radiation levels below the 25th percentile were classified as having a low level of MF nonionizing radiation exposure, whereas participants above the 25th percentile were considered to have high exposure.
Among the 1482 mother-child pairs (mean maternal age, 31.4±5.4 years) with complete radiation data, a significant proportion (n=620; 42.6%) of mothers reported alcohol use during pregnancy, and 137 (9.4%) reported smoking. Over 20 years of follow up, a total of 61 children (4.2%) received a diagnosis of ADHD. In regression models, offspring whose mothers had high radiation exposure had twice the risk for ADHD (adjusted hazard ratio [aHR], 2.01; 95% CI, 1.06-3.81) than offspring of mothers with low exposure. The association was stronger among children whose ADHD persisted into adolescence, or ≥12 years of age (aHR, 3.38; 95% CI, 1.43-8.02). Offspring with high in utero exposure were also more likely to have ADHD with immune-related comorbidities (aHR, 4.57; 95% CI, 1.61-12.99). When the analytic cohort was reduced to offspring with persistent ADHD only, the aHR of ADHD with immune-related comorbidities increased to 8.27 (95% CI, 1.96-34.79).
These findings corroborate prior studies suggesting that in utero exposure to radiation may increase the risk for ADHD, particularly ADHD with immune-related comorbidities. However, this study was limited by the fact that MF nonionizing radiation could only be measured during a single 24-hour period, rather than during the entirety of the pregnancy. As such, trends in exposure intensity could not be ascertained, and results should be extrapolated with care.
The investigators noted that their findings “reveal a possible new risk factor that is ubiquitous in our modern day lives.” Given the prevalence of MF nonionizing radiation exposure in daily life, the researchers emphasized the need for further research into the mechanisms through which radiation affects ADHD risk.
Li DK, Chen H, Ferber JR, Hirst AK, Odouli R. Association between maternal exposure to magnetic field nonionizing radiation during pregnancy and risk of attention-deficit/hyperactivity disorder in offspring in a longitudinal birth cohort [published online March 24, 2020]. JAMA Netw Open. doi: 10.1001/jamanetworkopen.2020.1417