Citation:

Nilsen, F. AND N. Tulve. A systematic review and meta-analysis examining the interrelationships between chemical and non-chemical stressors and inherent characteristics in children with ADHD. ENVIRONMENTAL RESEARCH. Elsevier B.V., Amsterdam, Netherlands, 180:108884, (2020). https://doi.org/10.1016/j.envres.2019.108884

Impact/Purpose:

This work investigated the discrepancies in children's public health data through analysis of chemical and non-chemical stressors, as well as genetic predisposition through systematic review and meta-analysis. We observe that chemical exposures, non-chemical stressors, and inherent characteristics influence children's mental health individually, and synergistically. The existing data highlights the need for interdisciplinary studies examining more than one type of stressor, as well as in depth analysis of individual stressors to better understand the complex interactions described in the literature. This work will aid future studies related to children's mental health through the research gaps identified and the recommendations made to further examine this complex issue.

Description:

Children may be more vulnerable to the combined interactions of chemical and non-chemical stressors from their built, natural, and social environments when compared to adults. Attention deficit/hyperactivity disorder (ADHD) is the most commonly diagnosed childhood neurodevelopmental disorder and is considered a major public health issue, as 75% of childhood cases persist into adulthood. ADHD is characterized by developmentally inappropriate levels of hyperactivity, impulsivity, and inattention, with the neurotransmitter serotonin regulating these symptoms. Monoamine oxidase A (MAOA) aids in serotonin uptake and is often implicated in behavioral and emotional disorders, including ADHD. When children are exposed to cigarette smoke, bisphenol A (BPA), or organophosphate pesticides, MAOA activity is inhibited. Non-chemical stressors, such as traumatic childhood experiences, and lifestyle factors, complicate the relationship between genotype and exposures to chemical stressors. But the co-occurrence among outcomes between exposures to chemical stressors, non-chemical stressors, and the low activity MAOA genotype suggest that mental illness in children may be influenced by multiple interacting factors. In this systematic review, we examine the existing literature that combines exposures to chemical and non-chemical stressors (specifically childhood trauma), MAOA characteristics, and ADHD diagnosis to investigate the interrelationships present. We observe that chemical (lead [Pb], phthalates/plasticizers, persistent organic pollutants, and cigarette smoke) exposure is significantly related to ADHD in children. We also observed that existing literature examining the interaction between MAOA, exposures to chemical stressors, and traumatic experiences and their effect on ADHD outcomes is sparse. We recommend that future studies investigating childhood ADHD include chemical and non-chemical stressors and inherent characteristics to gain a holistic understanding of childhood mental health outcomes.

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