August 1, 2024
Lead’s neurotoxicity is well established, and organophosphate pesticides were deliberately developed first as nerve agents in warfare and then as insecticides.
Noting that “Epidemiologic research on chemical exposures associated with the development of ADHD is numerous; however, studies have employed various methods, and, in some cases, have resulted in seemingly conflicting results,” a U.S. study team has performed an updated meta-analysis applying “identical meta-analytic techniques to the literature on the associations between earlier chemical exposures and later ADHD.”
Lead
Meta-analysis of eleven studies reporting dichotomous outcomes with a combined 7,566 participants found children exposed to lead were almost twice as likely to subsequently be diagnosed with ADHD as their unexposed peers.
A second meta-analysis, of thirteen studies reporting continuous outcomes with a total of 1,775 participants, found a small effect size increase in ADHD diagnosis from exposure to lead.
Interestingly, meta-analysis of four studies with a combined 4,360 participants found no association between prenatal lead exposure and subsequent ADHD diagnosis.
On the other hand, meta-analysis of seven studies combining almost five thousand participants reported that cumulative lead exposure more than doubled the likelihood of subsequent ADHD.
In other words, it’s not so much prenatal exposure as exposure after birth that is associated with increased risk.
Organophosphates
Meta-analysis of four studies reporting continuous outcomes with a combined total of 692 persons likewise found a small effect size increase in ADHD diagnosis from exposure to organophosphates.
Mercury
Meta-analysis of six studies reporting continuous outcomes with a combined total of over 17 thousand participants found a tiny effect size increase in ADHD diagnosis from exposure to mercury.
On the other hand, meta-analysis of ten studies reporting dichotomous outcomes with a combined total of over 650,000 persons found no association whatsoever between mercury exposure and subsequent diagnosis of ADHD.
Other exposures
Meta-analysis of five studies involving more than 34,000 participants found no evidence of an association between exposure to anesthesia and ADHD.
Meta-analysis of three studies encompassing 1,739 individuals found no evidence of an association between exposure to cadmium and ADHD.
Meta-analysis of four studies combining more than 2,400 persons found no evidence of an association between exposure to hexachlorobenzene and ADHD.
A pair of meta-analyses, one of three studies reporting dichotomous outcomes including 2,050 participants, the other of nine studies reporting continuous outcomes involving almost three thousand participants, both found no evidence of an association between exposure to polychlorinated biphenyls (PCBs) and ADHD.
There was little variability (heterogeneity) among results reported by individual studies within these meta-analyses, but a serious limitation was the failure to check for publication bias.
The authors concluded, “given our findings related to exposure to mercury, organophosphates, and PCBs, further research may be helpful to better characterize these relationships. Many of our effect sizes were small, which is consistent with the literature indicating that many genetic and environmental factors contribute to ADHD. … Furthermore, our findings support existing regulations of certain chemicals,” and “may inform future regulatory decisions”
Lina V. Dimitrov, Jennifer W. Kaminski, Joseph R. Holbrook, Rebecca H. Bitsko, Michael Yeh, Joseph G. Courtney, Brenna O’Masta, Brion Maher, Audrey Cerles, Katherine McGowan, and Margaret Rush, “A Systematic Review and Meta-analysis of Chemical Exposures and Attention-Deficit/Hyperactivity Disorder in Children,” Prevention Science (2024), 25 (Suppl 2):S225–S248, https://doi.org/10.1007/s11121-023-01601-6.
Given the persistence of ADHD and its adverse effects on children and adolescents, one might expect caregivers to face greater parenting challenges, with potential effects on their own mental health.
To what extent do parenting stress, depression, and – at the extreme – even suicidal ideation manifest themselves among caregivers of ADHD patients as opposed to caregivers of children and adolescents without ADHD?
A pair of Korean researchers made use of their country’s single-payer health insurance system, which maintains records on virtually the entire population, to perform a nationwide population study. They used data from the Korean National Health and Nutrition Examination Surveys (KNHANES) covering the decade from 2011 to 2020. KNHANES is an annual survey using a sophisticated sampling design conducted by the Korean Ministry of Health and Welfare to represent the entire population of South Korea.
The analysis included 14,428 individuals who had children younger than 19 at the time of participation. All were asked whether their child had ever been diagnosed with ADHD by a physician. The mental health problems of the parents were assessed in terms of perceived stress, depressive symptoms, and suicidality.
Of the 14,428 participants, 8,298 (57.5 %) were mothers and 6,130 (42.5 %) were fathers. Of the mothers, 116 (1.4 %) had a child with ADHD, and of the fathers, 86 (1.4 %) had a child with ADHD.
The researchers adjusted for the following confounders: age of caregiver, education level, household income, area of residence, employment status, alcohol consumption, smoking status, cohabitation status, number of children, and child’s age.
After adjustment, mothers of ADHD patients fared significantly worse than mothers of typically developing children on all three categories of mental health problems. They were 67% more likely to report higher stress, three times as likely to report symptoms of depression, and 2.5 times more likely to report suicidal ideation.
Yet that pattern did not carry over to fathers, where there was no significant difference in mental health indicators between fathers of children with ADHD and fathers of children without ADHD.
The authors concluded, “Parents of children with ADHD, especially mothers, need community support and public health attention to help alleviate their mental health problems.”
Background:
ADHD is commonly accompanied by psychiatric comorbidities that complicate its diagnosis and treatment. Roughly two out of three affected children and adolescents have one or more comorbid psychiatric disorder.
Because the peak age of ADHD onset is typically a decade or more earlier than those for schizophrenia, depressive disorder, or bipolar disorder, it is essential to explore these comorbidities over an extended period. Populations studies help researchers identify broader patterns and trends within an entire population and includes adults as well as children. This type of study provides unique insights into the population at large, rather than a sample group.
In earlier studies the maximum follow-up period was twelve years, insufficient in view of the roughly ten years between onset of ADHD and onset of major psychiatric disorders. Also, previous nationwide population studies have included less than 150,000 participants.
This study, relying on data from South Korea’s universal single-payer health insurance system, included over one and a half million individuals. Persons previously diagnosed with depression, bipolar disorder, tic disorder, or schizophrenia were excluded.
382,434 individuals had been diagnosed with ADHD, while 1,169,279 were without an ADHD diagnosis.
Propensity score matching ensured that potential confounders, both sociodemographic and clinical, were equalized for the ADHD and control groups. After matching, there were 353,898 individuals in each group.
After these adjustments, individuals in the ADHD group were at least an order of magnitude more likely to subsequently be diagnosed with psychiatric disorders than their peers without an ADHD diagnosis:
Conclusion:
The Korean study team concluded, “Overall, our findings suggest that upon prolonged examination, the risk of subsequent diagnoses of other psychiatric disorders in individuals with ADHD appears to be higher than that reported previously. … Therefore, patients with ADHD should be carefully screened for the presence of other psychiatric symptoms on a regular basis from an earlier age … It is advisable to have a follow-up period extending beyond 10 years to sufficiently identify the occurrence of comorbid disorders in patients with ADHD.”
Children with ADHD often face challenges in social interactions, leading to long-term consequences if not properly addressed. While various interventions exist, many fail to consider the broader social context in which these children interact. A recent study conducted in Bergen, Norway, explored how primary school teachers perceive their role in supporting children with ADHD who struggle socially and the strategies they use to assist them.
Researchers conducted semi-structured interviews with five focus groups of primary school teachers. Using reflexive thematic analysis, they identified two major themes:
Rather than relying on standardized interventions, teachers tailored their strategies to foster an inclusive and supportive social environment. Their methods included both active participation in social situations and behind-the-scenes efforts to encourage peer inclusion and understanding.
This study underscores the need to move beyond labels and recognize children with ADHD as individuals with distinct social needs. Teachers play a crucial role in shaping these children’s experiences, using flexible and personalized approaches to promote positive social interactions. By integrating social context and individualized support, educators can help children with ADHD build meaningful connections and navigate their social world more effectively.
_logo%201.svg)
