Association between exposure to air pollutants and attention-deficit hyperactivity disorder (ADHD) in children: a systematic review and meta-analysis

Chemical Pollutant Exposure in Neurodevelopmental Disorders: Integrating Toxicogenomic and Transcriptomic Evidence to Elucidate Shared Biological Mechanisms and Developmental Signatures

Rapid industrialization has introduced a range of chemicals into the environment, posing significant risks to fetal and child brain development. Using the Comparative Toxicogenomics Database (CTD), we constructed chemical exposome frameworks for seven neurodevelopmental disorders (NDDs) and identified chemical pollutants of epidemiological concern, including air pollutants (n = 8), toxic elements (n = 14), pesticides and related compounds (n = 18), synthetic organic chemicals (n = 16), and solvents (n = 5). Gene set enrichment analysis validated and revealed significant toxicogenomic associations between these chemical pollutants and NDDs, including autism spectrum disorder (ASD) (12 pollutants, proportional reporting ratio (PRR) 3.56-7.21) and intellectual disability (ID) (9 pollutants, PRR 3.13-5.59). Functional annotation of pollutant-specific gene sets highlighted shared biological processes, such as metabolic processes (e.g., xenobiotic metabolic process, xenobiotic catabolic process, and cytochrome P450 pathway) for ASD and cognitive processes (e.g., cognition, social behavior, and synapse assembly) for ID (Bonferroni-corrected p-values < 0.05). Time trajectory analysis of developmental transcriptomic data from the BrainSpan database for ASD (275 genes) and ID (93 genes) revealed three distinct expression patterns of chemical-pollutant-associated genes-higher prenatal, postnatal, and perinatal expression-indicating common and divergent underlying mechanisms across critical windows of chemical pollutant exposure.

Exposure to different types of residential greenness during pregnancy and early childhood and attention-deficit/hyperactivity disorder diagnosis: A nested case-control study

BACKGROUND

Epidemiological studies suggest that exposure to greenness may protect children attention-deficit/hyperactivity disorder (ADHD) diagnosis. However, evidence to date is limited while no previous research has independently investigated exposure to prenatal greenness.

OBJECTIVE

We conducted a nested case-control study with data from Born in Bradford (BiB) and INfancia y Medio Ambiente (INMA) birth cohorts to investigate the association between exposure to various types of residential greenness and ADHD diagnosis, considering both pregnancy and early childhood exposure periods independently. PM2.5 was tested as a potential mediator of the association.

METHODS

Children with ADHD were identified based on a confirmed medical diagnosis. Pregnancy and early childhood exposure to residential greenness were estimated through Normalized Difference Vegetation Index (NDVI) within 300-m, urban green space and natural green space percentages within 300-m, and the linear distance to the closest green space in meters. We performed a conditional logistic regression to analyze the association between the included greenness metrics and ADHD.

RESULTS

We found no statistically significant associations between any of the pregnancy and early childhood greenness metrics and ADHD diagnosis in the BiB cohort. Further analysis on the INMA cohort found that higher urban green space percentage slightly increased the risk of ADHD diagnosis during both pregnancy (total effects: OR 1.04, 95 % CI 1.01 to 1.07, p = 0.012; direct effects: OR 1.06, 95 % CI 1.03 to 1.10, p < 0.001) and early childhood (total effects: OR 1.03, 95 % CI 1.00 to 1.07, p = 0.042; direct effects: OR 1.04, 95 % CI 1.00 to 1.07, p = 0.033). However, these associations were not supported by the sensitivity analyses.

CONCLUSIONS

This study found both null and inconsistent associations between the included greenness metrics and ADHD. Further research is warranted to elucidate the potential role of exposure to different types of greenness in ADHD diagnosis.

The association of particulate matter PM2.5 and nitrogen oxides from ambient air pollution and mental health of children and young adults- a systematic review

INTRODUCTION

The developing brain, especially vulnerable during neuroplastic phases, is influenced by environmental and genetic factors. Understanding the impacts of air pollution on children's and young adults' mental health is an emerging research field.

CONTENT

This review systematically examines the adverse associations of ambient air pollutants on mental health. A database search using Scopus, EMBASE, Global Health, and PsycINFO included articles from 2013 onwards, following PRISMA guidelines. Of the 787 identified articles, 62 met the inclusion criteria. Quality was assessed using the EPHPP tool, and Best Evidence Synthesis (BES) evaluated the findings.

SUMMARY

The review found 36 associations between ambient air pollutants and adverse mental health outcomes across seven life-course exposure periods. Strong evidence linked early-life PM2.5 and NO2 exposures to Autism Spectrum Disorder (ASD) and childhood exposures to Attention Deficit Hyperactivity Disorder (ADHD). Significant, though inconsistent, associations were found between air pollutants and cognitive impairments, anxiety, depression, self-harm, and other behavioral problems. The heterogeneity of exposure limits and lack of experimental studies hinder causal assessment.

OUTLOOK

Compelling evidence links early-life and childhood exposure to PM2.5 and NO2 with ASD and ADHD. These findings highlight the need for public health policy changes and further research to explore these associations comprehensively.

The Effects of Air Pollution on Neurological Diseases: A Narrative Review on Causes and Mechanisms

Air pollution has well-documented adverse effects on human health; however, its impact on neurological diseases remains underrecognized. The mechanisms by which various components of air pollutants contribute to neurological disorders are not yet fully understood. This review focuses on key air pollutants, including particulate matter (PM2.5 and PM10), nitrogen dioxide (NO2), ozone (O3), carbon monoxide (CO), and diesel exhaust particles (DEPs). This paper summarizes key findings on the effects of air pollution on neurological disorders, including autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), Alzheimer's disease (AD), and Parkinson's disease (PD). Although the precise biological mechanisms remain to be fully elucidated, evidence suggests that multiple pathways are involved, including blood-brain barrier disruption, oxidative stress, inflammation, and the activation of microglia and astrocytes. This review underscores the role of environmental pollutants as significant risk factors for various neurological diseases and explores their mechanisms of action. By advancing our understanding of these interactions, this work aims to inform new insights for mitigating the adverse effects of air pollution on neurological diseases, ultimately contributing to the establishment of a cleaner and healthier environment for future generations.

Exploring the pathways linking prenatal and early childhood greenness exposure to attention-deficit/hyperactivity disorder symptoms during childhood: An approach based on robust causal inference

BACKGROUND

Epidemiological studies suggest that exposure to greenness during childhood may protect children from developing attention-deficit hyperactivity disorder (ADHD).

OBJECTIVE

We analyzed the effect of both prenatal (pregnancy) and early childhood (4-5-year follow-up) residential greenness exposure and green space availability on ADHD symptoms during childhood (up to the age of 12 years) and further explored the potential mediating role of PM2.5 and physical activity in the association.

METHODS

The study population included participants from the INfancia y Medio Ambiente (INMA) prospective birth cohort (Gipuzkoa, Sabadell, and Valencia). Average Normalized Difference Vegetation Index (NDVI) in buffers of 100-, 300- and 500-m around the residential addresses was used as an indicator of greenness, while green space availability was determined based on the presence of a major green space within 150-m from the residence. Childhood ADHD symptoms were assessed at the 6-8- and 10-12-year follow-ups using Conners Parents Rating Scale-Revised: Short Form.

RESULTS

Although no association was found for the prenatal exposure period, increased early childhood NDVI inversely associated with the OR of clinically significant ADHD symptoms during the 6-8-year follow-up at the 100-m (OR 0.03, 95% CI: 0.003 to 0.44), 300-m (OR 0.04, 95% CI: 0.003 to 0.42) and 500-m (OR 0.08, 95% CI: 0.01 to 0.76) buffers, but exclusively in the context of direct effects. Additionally, the 10-12-year follow-up analysis found moderate to weak evidence of potential total and direct effects of NDVI at both 100- and 300-m buffers on inattention scores, as well as for NDVI at the 300-m buffer on ADHD index scores. The analysis did not reveal evidence of mediation through PM2.5 or physical activity.

CONCLUSIONS

The evidence suggests that early childhood greenness exposure may reduce the risk of developing ADHD symptoms later in childhood, and that this association is not mediated through PM2.5 and physical activity.

Outdoor Air Pollution Relates to Amygdala Subregion Volume and Apportionment in Early Adolescents

Background

Outdoor air pollution is associated with an increased risk for psychopathology. Although the neural mechanisms remain unclear, air pollutants may impact mental health by altering limbic brain regions, such as the amygdala. Here, we examine the association between ambient air pollution exposure and amygdala subregion volumes in 9-10-year-olds.

Methods

Cross-sectional Adolescent Brain Cognitive DevelopmentSM (ABCD) Study® data from 4,473 participants (55.4% male) were leveraged. Air pollution was estimated for each participant's primary residential address. Using the probabilistic CIT168 atlas, we quantified total amygdala and 9 distinct subregion volumes from T1- and T2-weighted images. First, we examined how criteria pollutants (i.e., fine particulate matter [PM2.5], nitrogen dioxide, ground-level ozone) and 15 PM2.5 components related with total amygdala volumes using linear mixed-effect (LME) regression. Next, partial least squares correlation (PLSC) analyses were implemented to identify relationships between co-exposure to criteria pollutants as well as PM2.5 components and amygdala subregion volumes. We also conducted complementary analyses to assess subregion apportionment using amygdala relative volume fractions (RVFs).

Results

No significant associations were detected between pollutants and total amygdala volumes. Using PLSC, one latent dimension (LD) (52% variance explained) captured a positive association between calcium and several basolateral subregions. LDs were also identified for amygdala RVFs (ranging from 30% to 82% variance explained), with PM2.5 and component co-exposure associated with increases in lateral, but decreases in medial and central, RVFs.

Conclusions

Fine particulate and its components are linked with distinct amygdala differences, potentially playing a role in risk for adolescent mental health problems.

Impact of air pollution and climate change on mental health outcomes: an umbrella review of global evidence

The impact of air pollution and climate change on mental health has recently raised strong concerns. However, a comprehensive overview analyzing the existing evidence while addressing relevant biases is lacking. This umbrella review systematically searched the PubMed/Medline, Scopus and PsycINFO databases (up to June 26, 2023) for any systematic review with meta-analysis investigating the association of air pollution or climate change with mental health outcomes. We used the R metaumbrella package to calculate and stratify the credibility of the evidence according to criteria (i.e., convincing, highly suggestive, suggestive, or weak) that address several biases, complemented by sensitivity analyses. We included 32 systematic reviews with meta-analysis that examined 284 individual studies and 237 associations of exposures to air pollution or climate change hazards and mental health outcomes. Most associations (n=195, 82.3%) involved air pollution, while the rest (n=42, 17.7%) regarded climate change hazards (mostly focusing on temperature: n=35, 14.8%). Mental health outcomes in most associations (n=185, 78.1%) involved mental disorders, followed by suicidal behavior (n=29, 12.4%), access to mental health care services (n=9, 3.7%), mental disorders-related symptomatology (n=8, 3.3%), and multiple categories together (n=6, 2.5%). Twelve associations (5.0%) achieved convincing (class I) or highly suggestive (class II) evidence. Regarding exposures to air pollution, there was convincing (class I) evidence for the association between long-term exposure to solvents and a higher incidence of dementia or cognitive impairment (odds ratio, OR=1.139), and highly suggestive (class II) evidence for the association between long-term exposure to some pollutants and higher risk for cognitive disorders (higher incidence of dementia with high vs. low levels of carbon monoxide, CO: OR=1.587; higher incidence of vascular dementia per 1 μg/m3 increase of nitrogen oxides, NOx: hazard ratio, HR=1.004). There was also highly suggestive (class II) evidence for the association between exposure to airborne particulate matter with diameter ≤10 μm (PM10) during the second trimester of pregnancy and the incidence of post-partum depression (OR=1.023 per 1 μg/m3 increase); and for the association between short-term exposure to sulfur dioxide (SO2) and schizophrenia relapse (risk ratio, RR=1.005 and 1.004 per 1 μg/m3 increase, respectively 5 and 7 days after exposure). Regarding climate change hazards, there was highly suggestive (class II) evidence for the association between short-term exposure to increased temperature and suicide- or mental disorders-related mortality (RR=1.024), suicidal behavior (RR=1.012), and hospital access (i.e., hospitalization or emergency department visits) due to suicidal behavior or mental disorders (RR=1.011) or mental disorders only (RR=1.009) (RR values per 1°C increase). There was also highly suggestive (class II) evidence for the association between short-term exposure to increased apparent temperature (i.e., the temperature equivalent perceived by humans) and suicidal behavior (RR=1.01 per 1°C increase). Finally, there was highly suggestive (class II) evidence for the association between the temporal proximity of cyclone exposure and severity of symptoms of post-traumatic stress disorder (r=0.275). Although most of the above associations were small in magnitude, they extend to the entire world population, and are therefore likely to have a substantial impact. This umbrella review classifies and quantifies for the first time the global negative impacts that air pollution and climate change can exert on mental health, identifying evidence-based targets that can inform future research and population health actions.

Susceptible windows of prenatal and postnatal fine particulate matter exposures and attention-deficit hyperactivity disorder symptoms in early childhood

Few prior studies have explored windows of susceptibility to fine particulate matter (PM2.5) in both the prenatal and postnatal periods and children's attention-deficit/hyperactivity disorder (ADHD) symptoms. We analyzed data from 1416 mother-child pairs from the Spanish INMA (INfancia y Medio Ambiente) Study (2003-2008). Around 5 years of age, teachers reported the number of ADHD symptoms (i.e., inattention, hyperactivity/impulsivity) using the ADHD Diagnostic and Statistical Manual of Mental Disorders. Around 7 years of age, parents completed the Conners' Parent Rating Scales, from which we evaluated the ADHD index, cognitive problems/inattention, hyperactivity, and oppositional subscales, reported as age- and sex-standardized T-scores. Daily residential PM2.5 exposures were estimated using a two-stage random forest model with temporal back-extrapolation and averaged over 1-week periods in the prenatal period and 4-week periods in the postnatal period. We applied distributed lag non-linear models within the Bayesian hierarchical model framework to identify susceptible windows of prenatal or postnatal exposure to PM2.5 (per 5-μg/m3) for ADHD symptoms. Models were adjusted for relevant covariates, and cumulative effects were reported by aggregating risk ratios (RRcum) or effect estimates (βcum) across adjacent susceptible windows. A similar susceptible period of exposure to PM2.5 (1.2-2.9 and 0.9-2.7 years of age, respectively) was identified for hyperactivity/impulsivity symptoms assessed ~5 years (RRcum = 2.72, 95% credible interval [CrI] = 1.98, 3.74) and increased hyperactivity subscale ~7 years (βcum = 3.70, 95% CrI = 2.36, 5.03). We observed a susceptibility period to PM2.5 on risk of hyperactivity/impulsivity symptoms ~5 years in gestational weeks 16-22 (RRcum = 1.36, 95% CrI = 1.22, 1.52). No associations between PM2.5 exposure and other ADHD symptoms were observed. We report consistent evidence of toddlerhood as a susceptible window of PM2.5 exposure for hyperactivity in young children. Although mid-pregnancy was identified as a susceptible period of exposure on hyperactivity symptoms in preschool-aged children, this association was not observed at the time children were school-aged.

A systematic meta-review of systematic reviews on attention deficit hyperactivity disorder

BACKGROUND

There are now hundreds of systematic reviews on attention deficit hyperactivity disorder (ADHD) of variable quality. To help navigate this literature, we have reviewed systematic reviews on any topic on ADHD.

METHODS

We searched MEDLINE, PubMed, PsycINFO, Cochrane Library, and Web of Science and performed quality assessment according to the Joanna Briggs Institute Manual for Evidence Synthesis. A total of 231 systematic reviews and meta-analyses met the eligibility criteria.

RESULTS

The prevalence of ADHD was 7.2% for children and adolescents and 2.5% for adults, though with major uncertainty due to methodological variation in the existing literature. There is evidence for both biological and social risk factors for ADHD, but this evidence is mostly correlational rather than causal due to confounding and reverse causality. There is strong evidence for the efficacy of pharmacological treatment on symptom reduction in the short-term, particularly for stimulants. However, there is limited evidence for the efficacy of pharmacotherapy in mitigating adverse life trajectories such as educational attainment, employment, substance abuse, injuries, suicides, crime, and comorbid mental and somatic conditions. Pharmacotherapy is linked with side effects like disturbed sleep, reduced appetite, and increased blood pressure, but less is known about potential adverse effects after long-term use. Evidence of the efficacy of nonpharmacological treatments is mixed.

CONCLUSIONS

Despite hundreds of systematic reviews on ADHD, key questions are still unanswered. Evidence gaps remain as to a more accurate prevalence of ADHD, whether documented risk factors are causal, the efficacy of nonpharmacological treatments on any outcomes, and pharmacotherapy in mitigating the adverse outcomes associated with ADHD.

Fine particulate matter exposure and pediatric mental health outcomes: An integrative review

INTRODUCTION

Climate change is expected to worsen air pollution globally, which contributes to a multitude of negative health outcomes in humans.

AIM

The purpose of this integrative review is to examine the relationship between exposure to fine particulate matter (PM2.5 ) and mental health outcomes in children and adolescents.

METHODS

This review utilized Whittemore and Knafl's methodology for conducting an integrative review. After a thorough search of the literature, 17 articles were selected for this review and evaluated utilizing the Johns Hopkins Evidence Based Practice Appraisal Tool.

RESULTS

Of the 17 articles, all were quantitative observational study designs. The studies were then synthesized into four outcome themes. These themes included emergent and general psychiatric outcomes, neurodevelopmental disorders, stress and anxiety, and depression.

DISCUSSION

The strongest evidence supports a possible correlation between PM2.5 exposure and adolescent mental health outcomes, although there were some studies that contradicted these associations. While research on this topic is in its early stages, more needs to be conducted to determine causality with any of the associations presented to improve generalizability of the findings.

IMPLICATIONS FOR PRACTICE

Nurses must be aware of and part of the solution to address climate change and resulting air pollution, as it is a potentially significant threat to children's mental health in the 21st century.

Climate and Environmental Change: A Generation at Risk

ABSTRACT

Climate and environmental changes have been described as the biggest global health threat of the 21st century, with the potential to cause immediate harm in early life with important lifelong effects, and important consequences for future generations. Pregnant women and children are increasingly being recognized as vulnerable populations in the context of climate change. The effects can be direct or indirect through heat stress, extreme weather events, and air pollution, potentially affecting both the immediate and long-term health of pregnant women and newborns through a broad range of mechanisms. Climate and environmental changes have wide-ranging effects on a woman's reproductive life including sexual maturation and fertility, pregnancy outcomes, lactation, breastfeeding, and menopause. A comprehensive overview of these impacts is presented as well as opportunities for interventions for nurses practicing in perinatal, neonatal, midwifery, and pediatric specialties.

Joint polygenic and environmental risks for childhood attention-deficit/hyperactivity disorder (ADHD) and ADHD symptom dimensions

Background

attention-deficit/hyperactivity disorder (ADHD) is associated with both polygenic liability and environmental exposures, both intrinsic to the family, such as family conflict, and extrinsic, such as air pollution. However, much less is known about the interplay between environmental and genetic risks relevant to ADHD-a better understanding of which could inform both mechanistic models and clinical prediction algorithms.

Methods

Two independent data sets, the population-based Adolescent Brain Cognitive Development Study (ABCD) (N = 11,876) and the case-control Oregon-ADHD-1000 (N = 1449), were used to examine additive (G + E) and interactive (GxE) effects of selected polygenic risk scores (PRS) and environmental factors in a cross-sectional design. Genetic risk was measured using PRS for nine mental health disorders/traits. Exposures included family income, family conflict/negative sentiment, and geocoded measures of area deprivation, lead exposure risk, and air pollution exposure (nitrogen dioxide and fine particulate matter).

Results

ADHD PRS and family conflict jointly predicted concurrent ADHD symptoms in both cohorts. Additive-effects models, including both genetic and environmental factors, explained significantly more variation in symptoms than any individual factor alone (joint R 2 = .091 for total symptoms in ABCD; joint R 2 = .173 in Oregon-ADHD-1000; all delta-R 2 p-values <2e-7). Significant effect size heterogeneity across ancestry groups was observed for genetic and environmental factors (e.g., Q = 9.01, p = .011 for major depressive disorder PRS; Q = 13.34, p = .001 for area deprivation). GxE interactions observed in the full ABCD cohort suggested stronger environmental effects when genetic risk is low, though they did not replicate.

Conclusions

Reproducible additive effects of PRS and family environment on ADHD symptoms were found, but GxE interaction effects were not replicated and appeared confounded by ancestry. Results highlight the potential value of combining exposures and PRS in clinical prediction algorithms. The observed differences in risks across ancestry groups warrant further study to avoid health care disparities.

Prenatal Exposure to Air Pollutants and Attentional Deficit Hyperactivity Disorder Development in Children: A Systematic Review

Up to 9.5% of the world's population is diagnosed with attention deficit/hyperactivity disorder (ADHD), making it one of the most common childhood disorders. Air pollutants could be considered an environmental risk condition for ADHD, but few studies have specifically investigated the effect of prenatal exposure. The current paper reviews the studies conducted on the association between prenatal air pollutants (PM, NO_x, SO₂, O₃, CO and PAH) and ADHD development in children. From the 890 studies searched through PubMed, Google Scholar, Scopus, and Web of Science, 15 cohort studies met the inclusion criteria. NOS and WHO guidelines were used for quality and risk of bias assessment. The accumulative sample was 589,400 of children aged 3-15 years. Most studies reported an association between ADHD symptoms and prenatal PAH and PM exposure. Data available on NO₂ and SO₂ were inconsistent, whereas the effect of CO/O₃ is barely investigated. We observed heterogeneity through an odd ratio forest plot, and discrepancies in methodologies across the studies. Eight of the fifteen studies were judged to be of moderate risk of bias in the outcome measurement. In a nutshell, future studies should aim to minimize heterogeneity and reduce bias by ensuring a more representative sample, standardizing exposure and outcome assessments.

Ambient fine particulate exposure and subcortical gray matter microarchitecture in 9- and 10-year-old children across the United States

Neuroimaging studies showing the adverse effects of air pollution on neurodevelopment have largely focused on smaller samples from limited geographical locations and have implemented univariant approaches to assess exposure and brain macrostructure. Herein, we implement restriction spectrum imaging and a multivariate approach to examine how one year of annual exposure to daily fine particulate matter (PM2.5), daily nitrogen dioxide (NO2), and 8-h maximum ozone (O3) at ages 9-10 years relates to subcortical gray matter microarchitecture in a geographically diverse subsample of children from the Adolescent Brain Cognitive Development (ABCD) Study℠. Adjusting for confounders, we identified a latent variable representing 66% of the variance between one year of air pollution and subcortical gray matter microarchitecture. PM2.5 was related to greater isotropic intracellular diffusion in the thalamus, brainstem, and accumbens, which related to cognition and internalizing symptoms. These findings may be indicative of previously identified air pollution-related risk for neuroinflammation and early neurodegenerative pathologies.

Adverse Childhood Experiences (ACEs) and Environmental Exposures on Neurocognitive Outcomes in Children: Empirical Evidence, Potential Mechanisms, and Implications

The purpose of this article is to examine the current literature regarding the relationship between adverse childhood experiences (ACEs) and environmental exposures. Specifically, the paper will focus on how this relationship between ACEs and physical environmental factors impacts the neurocognitive development of children. With a comprehensive literary search focusing on ACEs, inclusive of socioeconomic status (SES), and environmental toxins common in urban environments, the paper explores how these factors contribute to cognitive outcomes that are associated with the environment and childhood nurturing. The relationship between ACEs and environmental exposures reveals adverse outcomes in children's neurocognitive development. These cognitive outcomes include learning disabilities, lowered IQ, memory and attention problems, and overall poor educational outcomes. Additionally, potential mechanisms of environmental exposures and children's neurocognitive outcomes are explored, referencing data from animal studies and evidence from brain imaging studies. This study further analyzes the current gaps in the literature, such as the lack of data focusing on exposure to environmental toxicants resulting from experiencing ACEs and discusses the research and social policy implications of ACEs and environmental exposure in the neurocognitive development of children.

Environmental pollution and attention deficit hyperactivity disorder: A meta-analysis of cohort studies

There is already knowledge of the extensive risk factors for attention deficit hyperactivity disorder (ADHD) and recent studies suggest that environmental pollution may contribute to an increase in the incidence of the disorder. The aim of our study was to perform a systematic review and meta-analysis of the risk of ADHD in people younger than 18 years old after exposure to environmental pollution. We searched the MEDLINE, Embase, SciELO, CINAHL, LILACS, Cochrane Central, and Web of Science databases and investigated the grey literature from inception until May 31, 2021. All cohort studies that provided data on exposure to environmental pollutants and ADHD in children and adolescents aged from zero to 18 years old were included. Two reviewers independently selected the studies and applied the quality criteria. If there was a divergence, a third reviewer contributed to the final decision. For the meta-analysis, risk ratios and their confidence intervals were calculated with the MetaXL 5.3 program, using the random effects model. In total, 21 articles were included in this systematic review, and 18 studies met the criteria for the meta-analysis, involving 134,619 participants. The meta-analysis suggested that children exposed to higher levels of heavy metal (RR: 2.41, 95% CI: 1.49-3.90), with low heterogeneity (I² = 39%), and lead (RR: 2.37, 95% CI: 1.28-4.40), with moderate heterogeneity (I² = 54%), are at greater risk of developing ADHD than those exposed to lower levels. This meta-analysis suggests that children exposed to higher levels of lead and heavy metal pollution are at greater risk of developing ADHD than those exposed to lower levels.

Association between Exposure to Particulate Matter Air Pollution during Early Childhood and Risk of Attention-Deficit/Hyperactivity Disorder in Taiwan

(1) Background: Recently, a growing number of studies have provided evidence to suggest a strong correlation between air pollution exposure and attention-deficit/hyperactivity disorder (ADHD). In this study, we assessed the relationship between early-life exposure to particulate matter (PM)₁₀, PM₂.₅, and ADHD; (2) Methods: The National Health Insurance Research Database (NHIRD) contains the medical records, drug information, inspection data, etc., of the people of Taiwan, and, thus, could serve as an important research resource. Air pollution data were based on daily data from the Environmental Protection Administration Executive Yuan, R.O.C. (Taiwan). These included particulate matter (PM_2.5 and PM₁₀). The two databases were merged according to the living area of the insured and the location of the air quality monitoring station; (3) Results: The highest levels of air pollutants, including PM_2.5 (adjusted hazard ratio (aHR) = 1.79; 95% confidence interval (CI) = 1.58-2.02) and PM₁₀ (aHR = 1.53; 95% CI = 1.37-1.70), had a significantly higher risk of ADHD; (4) Conclusions: As such, measures for air quality control that meet the WHO air quality guidelines should be strictly and uniformly implemented by Taiwanese government authorities.

The World Federation of ADHD International Consensus Statement: 208 Evidence-based conclusions about the disorder

BACKGROUND

Misconceptions about ADHD stigmatize affected people, reduce credibility of providers, and prevent/delay treatment. To challenge misconceptions, we curated findings with strong evidence base.

METHODS

We reviewed studies with more than 2000 participants or meta-analyses from five or more studies or 2000 or more participants. We excluded meta-analyses that did not assess publication bias, except for meta-analyses of prevalence. For network meta-analyses we required comparison adjusted funnel plots. We excluded treatment studies with waiting-list or treatment as usual controls. From this literature, we extracted evidence-based assertions about the disorder.

RESULTS

We generated 208 empirically supported statements about ADHD. The status of the included statements as empirically supported is approved by 80 authors from 27 countries and 6 continents. The contents of the manuscript are endorsed by 366 people who have read this document and agree with its contents.

CONCLUSIONS

Many findings in ADHD are supported by meta-analysis. These allow for firm statements about the nature, course, outcome causes, and treatments for disorders that are useful for reducing misconceptions and stigma.