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
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
Публикувано:March 24, 2020
Article Information
Accepted for Publication: January 30, 2020.
Published: March 24, 2020. doi:10.1001/jamanetworkopen.2020.1417
Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2020 Li D-K et al. JAMA Network Open.
"Abstract
Importance An association between maternal exposure to magnetic field (MF) nonionizing radiation during pregnancy and the risk of attention-deficit/hyperactivity disorder (ADHD) has been reported in both animal and human studies.
Objectives To determine whether maternal exposure to high levels of MF nonionizing radiation is associated with an increased risk of ADHD in offspring by using more accurate measurements of MF nonionizing radiation levels and physician-diagnosed ADHD, rather than self-reports, and to determine whether the association differs for the subtypes of ADHD with or without immune-related comorbidities.
Design, Setting, and Participants A longitudinal birth cohort study was conducted at Kaiser Permanente Northern California among 1482 mother-child pairs whose mothers were participants of an existing birth cohort and whose level of exposure to MF nonionizing radiation was captured during pregnancy in 2 studies conducted from October 1, 1996, to October 31, 1998, and from May 1, 2006, to February 29, 2012. The offspring were followed up from May 1, 1997, to December 31, 2017.
Exposure All participating women wore a monitoring meter for 24 hours during pregnancy to capture the level of exposure to MF nonionizing radiation from any sources.
Main Outcomes and Measures Physician-diagnosed ADHD and immune-related comorbidities of asthma or atopic dermatitis up to 20 years of age in offspring captured in the Kaiser Permanente Northern California electronic medical record from May 1, 1997, to December 31, 2017. Confounders were ascertained during in-person interviews during pregnancy. "
Question
Could human exposure to magnetic field nonionizing radiation
be associated with increased risk of attention-deficit/hyperactivity
disorder in children?
Findings This birth cohort study found a statistically significant association between a high level of maternal exposure to magnetic field nonionizing radiation, as captured with a monitoring meter, during pregnancy and an increased risk of attention-deficit/hyperactivity disorder in offspring. The association was stronger for children who received a diagnosis of attention-deficit/hyperactivity disorder in adolescence (≥12 years of age) than for those without such a diagnosis in adolescence, and primarily for children with attention-deficit/hyperactivity disorder with immune-related comorbidities.
Meaning The findings should spur more research to examine the biological association of in utero magnetic field exposure with risk of attention-deficit/hyperactivity disorder in offspring.
Importance
An association between maternal exposure to magnetic field
(MF) nonionizing radiation during pregnancy and the risk of
attention-deficit/hyperactivity disorder (ADHD) has been reported in
both animal and human studies.
Objectives To determine whether maternal exposure to high levels of MF nonionizing radiation is associated with an increased risk of ADHD in offspring by using more accurate measurements of MF nonionizing radiation levels and physician-diagnosed ADHD, rather than self-reports, and to determine whether the association differs for the subtypes of ADHD with or without immune-related comorbidities.
Design, Setting, and Participants A longitudinal birth cohort study was conducted at Kaiser Permanente Northern California among 1482 mother-child pairs whose mothers were participants of an existing birth cohort and whose level of exposure to MF nonionizing radiation was captured during pregnancy in 2 studies conducted from October 1, 1996, to October 31, 1998, and from May 1, 2006, to February 29, 2012. The offspring were followed up from May 1, 1997, to December 31, 2017.
Exposure All participating women wore a monitoring meter for 24 hours during pregnancy to capture the level of exposure to MF nonionizing radiation from any sources.
Main Outcomes and Measures Physician-diagnosed ADHD and immune-related comorbidities of asthma or atopic dermatitis up to 20 years of age in offspring captured in the Kaiser Permanente Northern California electronic medical record from May 1, 1997, to December 31, 2017. Confounders were ascertained during in-person interviews during pregnancy.
Results Among the 1454 mother-child pairs (548 white [37.7%], 110 African American [7.6%], 325 Hispanic [22.4%], 376 Asian or Pacific Islander [25.9%], and 95 other or unknown [6.5%]; mean [SD] maternal age, 31.4 [5.4] years]), 61 children (4.2%) had physician-diagnosed ADHD. Using Cox proportional hazards regression to account for follow-up time and confounders, compared with children whose mothers had a low level of exposure to MF nonionizing radiation during pregnancy, children whose mothers were exposed to higher levels of MF nonionizing radiation had more than twice the risk of ADHD (adjusted hazard ratio [aHR], 2.01; 95% CI, 1.06-3.81). The association was stronger for ADHD that persisted into adolescence (≥12 years of age), with an aHR of 3.38 (95% CI, 1.43-8.02). When the subtypes of ADHD were examined, the association existed primarily for ADHD with immune-related comorbidities (asthma or atopic dermatitis), with an aHR of 4.57 (95% CI, 1.61-12.99) for all ADHD cases and an aHR of 8.27 (95% CI, 1.96-34.79) for persistent cases of ADHD.
Conclusions and Relevance Consistent with the emerging literature, this study suggests that in utero exposure to high levels of MF nonionizing radiation was associated with an increased risk of ADHD, especially ADHD with immune-related comorbidity. The findings should spur more research to examine the biological association of in utero MF exposure with risk of ADHD in offspring, given that almost everyone is exposed to it.
Findings This birth cohort study found a statistically significant association between a high level of maternal exposure to magnetic field nonionizing radiation, as captured with a monitoring meter, during pregnancy and an increased risk of attention-deficit/hyperactivity disorder in offspring. The association was stronger for children who received a diagnosis of attention-deficit/hyperactivity disorder in adolescence (≥12 years of age) than for those without such a diagnosis in adolescence, and primarily for children with attention-deficit/hyperactivity disorder with immune-related comorbidities.
Meaning The findings should spur more research to examine the biological association of in utero magnetic field exposure with risk of attention-deficit/hyperactivity disorder in offspring.
Abstract
Objectives To determine whether maternal exposure to high levels of MF nonionizing radiation is associated with an increased risk of ADHD in offspring by using more accurate measurements of MF nonionizing radiation levels and physician-diagnosed ADHD, rather than self-reports, and to determine whether the association differs for the subtypes of ADHD with or without immune-related comorbidities.
Design, Setting, and Participants A longitudinal birth cohort study was conducted at Kaiser Permanente Northern California among 1482 mother-child pairs whose mothers were participants of an existing birth cohort and whose level of exposure to MF nonionizing radiation was captured during pregnancy in 2 studies conducted from October 1, 1996, to October 31, 1998, and from May 1, 2006, to February 29, 2012. The offspring were followed up from May 1, 1997, to December 31, 2017.
Exposure All participating women wore a monitoring meter for 24 hours during pregnancy to capture the level of exposure to MF nonionizing radiation from any sources.
Main Outcomes and Measures Physician-diagnosed ADHD and immune-related comorbidities of asthma or atopic dermatitis up to 20 years of age in offspring captured in the Kaiser Permanente Northern California electronic medical record from May 1, 1997, to December 31, 2017. Confounders were ascertained during in-person interviews during pregnancy.
Results Among the 1454 mother-child pairs (548 white [37.7%], 110 African American [7.6%], 325 Hispanic [22.4%], 376 Asian or Pacific Islander [25.9%], and 95 other or unknown [6.5%]; mean [SD] maternal age, 31.4 [5.4] years]), 61 children (4.2%) had physician-diagnosed ADHD. Using Cox proportional hazards regression to account for follow-up time and confounders, compared with children whose mothers had a low level of exposure to MF nonionizing radiation during pregnancy, children whose mothers were exposed to higher levels of MF nonionizing radiation had more than twice the risk of ADHD (adjusted hazard ratio [aHR], 2.01; 95% CI, 1.06-3.81). The association was stronger for ADHD that persisted into adolescence (≥12 years of age), with an aHR of 3.38 (95% CI, 1.43-8.02). When the subtypes of ADHD were examined, the association existed primarily for ADHD with immune-related comorbidities (asthma or atopic dermatitis), with an aHR of 4.57 (95% CI, 1.61-12.99) for all ADHD cases and an aHR of 8.27 (95% CI, 1.96-34.79) for persistent cases of ADHD.
Conclusions and Relevance Consistent with the emerging literature, this study suggests that in utero exposure to high levels of MF nonionizing radiation was associated with an increased risk of ADHD, especially ADHD with immune-related comorbidity. The findings should spur more research to examine the biological association of in utero MF exposure with risk of ADHD in offspring, given that almost everyone is exposed to it.
Introduction
Approximately 11% of all children aged 4 to 17 years
(>6.4 million children) in the United States receive a diagnosis of,
or treatment for, attention-deficit/hyperactivity disorder (ADHD).1
Attention-deficit/hyperactivity disorder has been associated with poor
school performance during childhood and with lifelong disabilities.2
According to the Centers for Disease Control and Prevention, the annual
costs associated with ADHD treatment and care are estimated at $42
billion1,3,4 (and as high as $124 billion when burden to the family is included).5,6
The most troubling aspect of pediatric ADHD is that its prevalence has
been steadily increasing during the last few decades, with acceleration
since 2000.7
Without ruling out genetic susceptibility, such a secular increase
points to the presence of important environmental risk factors.
One of the most relevant time windows for environmental
risk factors to be associated with brain development is during
pregnancy, when fetal brain development is susceptible to external
insults that could have a long-lasting effect on brain function and
neurobehavior. Among the limited research into the causes of ADHD
associated with in utero environmental exposures, to our knowledge, the
focus has thus far been on chemicals.8
One nonchemical factor that has not been examined is the ever-present
nonionizing radiation, also known as magnetic fields (MFs), emitted from
electric appliances, power lines, and wireless devices and networks
including cell phone towers. Emerging human studies have begun to report
that maternal exposure to MF nonionizing radiation during pregnancy is
associated with an increased risk of several childhood illnesses,
including immune-related conditions (such as asthma),9 obesity,10 and neurologic conditions (such as ADHD).11,12 An experimental study13
provided further evidence of (1) the direct link between in utero
exposure to MF nonionizing radiation and ADHD in offspring and (2) a
potential mechanism linking in utero exposure of MF nonionizing
radiation with ADHD through altered neuronal developmental programming.
Additional evidence from experimental animal studies has also recently
been reported.14 Finally, a JAMA report showed that MF nonionizing radiation could affect human brain cell functions.15,16
The emerging evidence indicates that (1) there is a potentially adverse
biological association between in utero exposure to MF nonionizing
radiation and the health of offspring and (2) fetal brain development
and programming is likely one of the vulnerable targets associated with
in utero exposure to MF nonionizing radiation.
If research evidence shows that in utero MF nonionizing
radiation exposure is a risk factor for ADHD, then this exposure would
be a modifiable risk factor. Although almost everyone today is exposed
to MF nonionizing radiation to some degree, prevention measures can be
implemented to reduce the level of maternal MF nonionizing radiation
exposure during pregnancy. Thus, understanding the association between
in utero exposure to MF nonionizing radiation and the risk of ADHD would
be an important first step. To further examine the association and
improve on weaknesses in previous studies, we conducted a prospective
birth cohort study with focuses on (1) an objective measurement of
maternal exposure to MF nonionizing radiation during pregnancy and (2) a
more accurate determination of ADHD cases through a physician’s
diagnosis as opposed to maternal self-reporting.
Methods
Study Design and Participants
This study was based on the participants of an existing
birth cohort of the Kaiser Permanente Northern California (KPNC) health
care delivery system whose members have repeatedly been shown to be
representative of the underlying community population.17,18
The mothers were pregnant women who participated in 2 previous studies
(one conducted from October 1, 1996, to October 31, 1998, and the other
from May 1, 2006, to February 29, 2012) that followed the same study
protocol. The level of MF nonionizing radiation exposure was measured by
asking participants to wear a monitoring meter throughout a 24-hour
monitoring period during pregnancy. Their offspring were followed up
from May 1, 1997, to December 31, 2017. The study was approved by the
KPNC Institutional Review Board, and all participants provided written
informed consent. This study followed the Strengthening the Reporting of
Observational Studies in Epidemiology (STROBE) reporting guidelines.
Recruitment of Pregnant Women
All pregnant KPNC members aged 18 years or older who
resided in the San Francisco Bay Area counties were identified through
KPNC electronic medical record data. Those who intended to carry the
pregnancy to term at the time of recruitment were eligible for
participation in the study. All participants were asked to wear a meter
that captured the level of MF nonionizing radiation exposure during a
24-hour monitoring period. An in-person interview was also conducted to
ascertain risk factors and potential confounders at the same time. Of
2060 participating pregnant women who had valid measurements for MF
nonionizing radiation levels during pregnancy, 1568 delivered live-born
offspring, while the rest of the pregnancies ended mostly owing to
miscarriage. After excluding those whose offspring did not receive
pediatric care at KPNC after delivery, 1482 mother-child dyads were
eligible for the present study (eFigure in the Supplement).
Measuring Levels of Exposure to MF Nonionizing Radiation During Pregnancy
Once a pregnant woman had given consent to participate in the study, she was asked to wear an EMDEX meter (Enertech Inc)9,10,19,20
to capture the level of MF nonionizing radiation exposure. During the
24-hour monitoring period, which occurred during the first or second
trimester, the meters (EMDEX II and EMDEX Lite) captured levels of 40 to
800 Hz of MF nonionizing radiation encountered by the participating
woman throughout her daily life. The MF nonionizing radiation level was
measured in milligauss. To avoid potential measurement biases, the
meters were calibrated before each use and programmed to show only the
time of day, without displaying any MF nonionizing radiation exposure
level, so that participants were not aware of their MF nonionizing
radiation levels during the measurement period. This design was
implemented to avoid changes in any routine daily activities owing to
the MF nonionizing radiation level being displayed.
The level of MF exposure has been reported to be
relatively stable when measured repeatedly over 12 to 26 months, and the
study concluded that the measurement of the MF nonionizing radiation
level on a single visit is a good indicator of personal exposure levels
during a period of up to 26 months.21
In our study, we also conducted repeated measurements among a subset of
94 participants, and the correlation coefficient was 0.6 between 2
repeated measurements of MF nonionizing radiation, indicating a
relatively stable exposure level during pregnancy.
To examine the association of high levels of MF
nonionizing radiation with risk of ADHD, we used the 90th percentile of
the 24-hour measurements as the MF index, which reflects the MF
nonionizing radiation level at or above which a participant was exposed
to for 10% of the time during the day. Given that everyone is exposed to
MF nonionizing radiation at some levels, to classify participating
women into low or high MF nonionizing radiation exposure groups, based
on the experience of previous studies,9,10,19
we used a cutoff based on the 25th percentile of the MF index’s
distribution, which corresponded to 1.3 mG. The participants whose MF
nonionizing radiation level was lower than 1.3 mG were classified as
having a low level of MF nonionizing radiation exposure during
pregnancy, while the participants whose MF nonionizing radiation level
was 1.3 mG or higher were classified as having a relatively higher daily
level of MF nonionizing radiation exposure.
Outcome Measurement: ADHD Diagnosis and Immune-Related Comorbidities
All eligible participating children included in the
study were followed up to 20 years of age until (1) they received a
diagnosis of ADHD, (2) they left the KPNC system, or (3) the study
period ended (at the end of 2017). Unlike many previous studies based on
self-report, the determination of ADHD in this study was based on a
physician’s diagnosis recorded in the KPNC electronic medical records. A
diagnosis of ADHD was identified through International Classification of Diseases, Ninth Revision (ICD-9) code 314.x or International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10)
code F90.x. To avoid ambiguous cases that might have had temporary
symptoms similar to ADHD, a child was considered to have had ADHD if
there were 2 or more ADHD diagnoses that were at least 1 year apart. We
excluded 28 children who had only 1 diagnosis. Thus, the final analyses
included 1454 mother-child dyads. To enhance the accuracy of our ADHD
case definition, we further identified children who had an ADHD
diagnosis that persisted into adolescence (≥12 years of age; persistent
cases). The persistent cases were more likely to be true and more severe
cases of ADHD. If the exposure of MF nonionizing radiation during
pregnancy was associated with ADHD and not with other factors (eg,
confounders), one would expect to observe a stronger association with
persistent (true) ADHD cases. Thus, confirmation of a stronger
association with persistent cases of ADHD than with cases of children
with ADHD who did not receive the diagnosis in adolescence could
strengthen the observed association.
In addition, emerging literature has shown that some
individuals with ADHD have a higher concurrence of immune-related
comorbidities, such as asthma and atopic dermatitis (AD); thus, an
immune-related cause for ADHD has been proposed.22-28 At the same time, MF nonionizing radiation exposure has been reported to have an association with the immune system.9,29-33
Thus, it is conceivable that in utero exposure to MF nonionizing
radiation may specifically increase the risk of ADHD with an underlying
immune cause. To examine this potential causal pathway, we divided
children with ADHD into those with immune-related comorbidities (asthma
or AD), as reported in the literature,23-27 and those without these comorbidities. Both asthma and AD were identified based on physicians’ diagnoses: ICD-9 codes of 493.x or ICD-10 codes of J45.x for asthma and ICD-9 codes of 691.8x or ICD-10
codes of L20.x for AD (excluding diaper or skin rash). A stronger
association with ADHD cases with immune-related comorbidity, combined
with a lack of association with ADHD cases without immune-related
comorbidity, would strengthen the biological basis for the association
between in utero exposure to MF nonionizing radiation and risk of ADHD
because it would be consistent with the underlying mechanistic pathway.
Potential Confounders
In-person interviews were conducted with all
participants during their pregnancy to ascertain information on many
potential confounders. We evaluated several risk factors for ADHD as
potential confounders, including maternal age, race/ethnicity,
educational level, prenatal smoking and alcohol use, prepregnancy body
mass index, sex of offspring, and sociodemographic characteristics.
Statistical Analysis
The Cox proportional hazards regression model was used
to control for potential confounders. The Cox survival analysis also has
the advantage of accounting for differing durations of follow-up for
offspring. All children were followed up starting from birth until (1)
they received a diagnosis of ADHD or (2) they were censored (ie, either
left the KPNC system or did not have an ADHD diagnosis at the end of the
study). We first examined the association between the level of maternal
MF nonionizing radiation exposure (high vs low) and the risk of ADHD
including all children. We then examined the association for persistent
ADHD cases to assess the robustness of the association. Finally, we
examined the association separately for ADHD cases with or without the
immune-related comorbidities of asthma or AD.
We used the change-in-estimate criterion to identify
confounders based on whether the ADHD hazard ratio for MF nonionizing
radiation changed by 10% or more when the potential confounder was
introduced into the model. A Kaplan-Meier survival curve was used to
present the ADHD survival pattern separately for offspring with high or
low levels of in utero exposure to MF nonionizing radiation. Consistent
with previous studies examining the effect of MF nonionizing radiation,9,10,19,20,34
we did not identify any factors that met the definition for being a
confounder using the change-in-estimate criterion. Nevertheless, we
included in the model common sociodemographic characteristics, such as
maternal age, educational level, and race/ethnicity, as well as some
known risk factors for ADHD, such as maternal smoking and alcohol use
during pregnancy, prepregnancy body mass index, and sex of offspring.
All P values were from 2-sided tests and results were deemed statistically significant at P < .05.
Results
The mean (SD) maternal age of the study population was
31.4 (5.4) years; the racial/ethnic distribution was 548 white (37.7%),
110 African American (7.6%), 325 Hispanic (22.4%), 376 Asian or Pacific
Islander (25.9%), and 95 other or unknown (6.5%); 137 (9.4%) reported
smoking during pregnancy, and 620 (42.6%) reported alcohol use during
pregnancy. Table 1
presents the characteristics of participants based on their high or low
levels of MF nonionizing radiation exposure. As similarly shown in
previous studies,9,10,19,20,34
the level of MF nonionizing radiation exposure was not associated with
commonly known ADHD risk factors or socioeconomic characteristics,
including maternal smoking and alcohol use during pregnancy, maternal
history of ADHD, educational level, marital status, household income,
sex of offspring, and breastfeeding history. Among all the factors
examined in Table 1,
only maternal age and prepregnancy body mass index showed a
statistically significant difference between the 2 groups. Thus, the 2
MF nonionizing radiation exposure groups (the high level and low level)
were comparable in all other examined factors that may be associated
with the risk of ADHD. In addition, the amount of follow-up time (loss
to follow-up) was comparable between the 2 exposure cohorts; by the end
of the study (up to 20 years of follow-up), 73.6% (421 of 572) of the
participants in the low-level exposure group and 65.1% (574 of 882) of
the participants in the high-level exposure group remained within the
KPNC system.
A total of 61 children (4.2%) had physician-diagnosed
ADHD. After adjustment for known risk factors for ADHD, including
maternal age, educational level, race/ethnicity, maternal smoking and
alcohol use during pregnancy, prepregnancy body mass index, and sex of
offspring, Table 2
shows that, for all cases of ADHD, maternal daily exposure to higher
levels of MF nonionizing radiation (≥1.3 mG) during pregnancy was
associated with more than 2 times greater hazard of offspring receiving
an ADHD diagnosis, with an adjusted hazard ratio of 2.01 (95% CI,
1.06-3.81). When examining the association separately for children with
ADHD who had or had not received the diagnosis during adolescence, we
found a stronger association for persistent ADHD, with an adjusted
hazard ratio of 3.38 (95% CI, 1.43-8.02), whereas there was no
association for children who no longer had an ADHD diagnosis in
adolescence (Table 3).
Given the previously reported associations of MF
nonionizing radiation exposure with immune-related diseases and the
existence of potential ADHD immune-related causes, we further examined
the association of in utero exposure to MF nonionizing radiation with
the risk of ADHD separately for children with ADHD and immune-related
comorbidities (asthma or AD diagnosis) and children with ADHD without
such comorbidities. Table 4
shows the results for all children with ADHD and for children with
persistent ADHD. The results show that in utero exposure to MF
nonionizing radiation was associated with an increased risk of ADHD
primarily for children with immune-related comorbidities of asthma
and/or AD, with more than 4 times the risk of ADHD with immune-related
comorbidities (adjusted hazard ratio, 4.57; 95% CI, 1.61-12.99). The
association was even stronger for persistent ADHD with immune-related
comorbidities (adjusted hazard ratio, 8.27; 95% CI, 1.96-34.79). In
contrast, no association was observed for children with ADHD without
immune-related comorbidities. We also provided the results stratified by
immune-related comorbidities in the eTable in the Supplement. The results are consistent with those in Table 4, although the interpretation of the stratified results could be different.
The Figure
provides the Kaplan-Meier survival curve showing the proportion of
offspring who remained free of ADHD with immune-related comorbidity
throughout childhood, from birth up to 20 years of age. This graph shows
that, starting at an early age when ADHD was normally diagnosed (around
5 years of age), there was a separation of the ADHD survival
probability between the 2 MF nonionizing radiation exposure groups.
Offspring whose mothers were exposed to high levels of MF nonionizing
radiation during pregnancy had a consistently higher risk of ADHD (lower
probability of remaining ADHD free) throughout childhood compared with
offspring whose mothers were exposed to lower levels of MF nonionizing
radiation during pregnancy.
Discussion
In this large birth cohort study of 1454 mother-child
dyads with rarely available data on maternal MF nonionizing radiation
exposure during pregnancy captured with a monitoring meter, we followed
up the offspring of participating women for physician-diagnosed ADHD and
immune-related comorbidities (asthma and AD) up to 20 years of age. We
observed that in utero exposure to higher levels of MF nonionizing
radiation was associated with more than 2 times the risk of ADHD. The
association became stronger for children with persistent ADHD whose
condition remained present into adolescence (Table 3).
The observed association was mainly for children with ADHD and
concurrent immune-related comorbidities (asthma and/or AD), which is
consistent with the reported association between exposure to MF
nonionizing radiation and the immune system.9,29-32
Thus, in addition to the overall association, the additional
observations of a stronger association with persistent ADHD and ADHD
with current immune-related comorbidities are consistent with the
underlying biological plausibility and strengthen the observed
association.
Given the limited understanding of the causes of ADHD,
these findings could lead to a new research direction to elucidate
environmental risk factors for ADHD during fetal development. These new
findings would need to be replicated in future studies. If confirmed,
the increasingly ubiquitous exposure to MF nonionizing radiation in
human populations, including pregnant women, could be an important,
nonetheless modifiable, risk factor for ADHD. Currently, the causes and
the secular increase in incidence of ADHD remain poorly understood.
Although understanding its pathologic pathways remains
limited at this point, in utero exposure to MF nonionizing radiation has
been associated with neuropathologic changes in the brain,13
especially in the prefrontal cortex, including impaired glutamatergic
synaptic transmission onto layer V pyramidal neurons of the prefrontal
cortex. Thus, there is biological plausibility for in utero exposure to
MF nonionizing radiation to increase the risk of ADHD in offspring
through fetal development of both the brain and the immune system.
Given that the exposure of interest was maternal MF
nonionizing radiation exposure during pregnancy, the factors that
existed after birth, by definition, cannot act as confounders because
they occurred after the exposure; thus, they are likely on the causal
pathway. Other factors (eg, demographic characteristics and maternal
smoking and alcohol use) did not meet the criteria of being a confounder
to be associated with both the MF nonionizing radiation exposure and
ADHD, as already described. Nevertheless, we included them in the
regression models, and adjustment for those variables did not change the
results.
Limitations and Strengths
This study has some limitations. Despite the
significantly improved accuracy of our MF nonionizing radiation exposure
measurements compared with previous studies, we were not able to ask
women to carry the meter throughout pregnancy because it was not
feasible. Thus, there may still be some inaccuracy in maternal MF
nonionizing radiation exposure level. Given that this was a prospective
study design, maternal MF nonionizing radiation exposure was ascertained
during pregnancy before ADHD diagnosis in offspring. Any measurement
inaccuracy, if it existed, would have been nondifferential (ie, not
associated with the ADHD outcome). In principle, nondifferential
measurement error would have attenuated the observed association. In
other words, without the measurement error, the observed association
would have been even stronger. In addition, the study measured MF
nonionizing radiation at a low frequency (≤800 Hz); thus, the findings
may not apply to MF nonionizing radiation at higher frequencies.
This study also has some strengths, including (1) a
prospective design, thus reducing the likelihood of participation bias;
(2) physician-diagnosed, rather than self-reported, ADHD, thus
increasing the accuracy of outcome measurement; and (3) an objective
measure of maternal MF nonionizing radiation level ascertained by a
meter to reduce measurement error for the exposure.
Conclusions
Using a longitudinal birth cohort study design, we
examined the association between maternal exposure to MF nonionizing
radiation during pregnancy and risk of ADHD in offspring throughout
childhood up to age 20 years. The study improved over previous studies
by enhancing the accuracy of measuring MF nonionizing radiation exposure
and of ADHD diagnosis. The findings provide new evidence that in utero
exposure to a high level of MF nonionizing radiation is associated with
an increased risk of ADHD in offspring. The association is primarily
between MF nonionizing radiation exposure and ADHD with immune-related
comorbidities and persistent cases of ADHD. The findings reveal a
possible new risk factor that is ubiquitous in our modern day lives and
should spur more research to examine this potential association.
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Article Information
Accepted for Publication: January 30, 2020.
Published: March 24, 2020. doi:10.1001/jamanetworkopen.2020.1417
Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2020 Li D-K et al. JAMA Network Open.
Concept and design: Li.
Acquisition, analysis, or interpretation of data: All authors.
Drafting of the manuscript: Li.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: Li, Chen, Ferber, Hirst.
Obtained funding: Li.
Administrative, technical, or material support: Li, Ferber, Odouli.
Supervision: Li.
Conflict of Interest Disclosures: None reported.
Funding/Support:
This study was supported through funds provided by the National
Institute of Environmental Health Sciences and the California Public
Health Foundation.
Role of the Funder/Sponsor:
The funding sources had no role in the design and conduct of the study;
collection, management, analysis, and interpretation of the data;
preparation, review, or approval of the manuscript; and decision to
submit the manuscript for publication.
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