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A landmark nationwide study from South Korea has uncovered a significant link between prenatal exposure to air pollution — specifically nitrogen dioxide (NO2) — and an increased risk of ADHD in children.
While researchers have long suspected that air pollutants interfere with fetal brain development through inflammation and oxidative stress, this study is one of the largest and most comprehensive of its kind, following nearly 1.5 million births for up to 13 years.
Why South Korea?
South Korea provided a unique countrywide “laboratory” for this research due to two key infrastructure strengths:
Key Findings: The “Smoking Gun” of NO2
While the study looked at several pollutants, nitrogen dioxide — a byproduct of fossil fuel combustion in cars and power plants — emerged as the primary concern.
Pollutant
Association with ADHD Risk
Nitrogen Dioxide (NO2)
Strongest Link: Every 1-ppb (part-per-billion) increase in exposure linked to a 22% rise in risk.
Sulfur Dioxide (SO2)
Minimal Link: Only a slight 4% increase per ppb.
Ozone (O3) carbon monoxide (CO), & particulates
No significant association was found.
The scale of the NO2 risk is particularly striking. Over the typical range of exposure levels found in the study (an interquartile range of 13 ppb), the data suggest a threefold increase in ADHD risk for children in the highest-exposure groups compared to the lowest.
Accounting for Other Factors
To ensure the results weren’t skewed by other variables, the researchers controlled for a wide range of confounders including:
The authors emphasized the strong association between maternal nitrogen dioxide exposure and ADHD, while also noting the small but significant association with sulfur dioxide.
The Take-Away: A New Frontier for Public Health
Historically, air quality laws have been designed to protect our lungs and hearts. However, this study adds to a growing body of evidence suggesting that the brain is likewise vulnerable.
In a commentary on the findings, expert George Ayoub argued that “neurodevelopment should be explicitly considered” when governments perform cost-benefit analyses on air quality regulation. My view is a bit different. The association is intriguing but the study does not establish cause and effect. Many statistically significant environmental risk associations for neurodevelopmental disorders have disappeared after controlling for maternal risk for ADHD. I hope this research team will do those analyses if feasible.
Tak Kyu Oh and In-Ae Song, “Prenatal exposure to ambient air pollution and risk of neurodevelopmental disorders in offspring: A nationwide population-based cohort study,” Journal of Child Psychology and Psychiatry (2026), published online, https://doi.org/10.1111/jcpp.70120.
George Ayoub, “Prenatal exposure to ambient air pollution and risk of neurodevelopmental disorders in offspring: A nationwide population‐based cohort study – A commentary on Oh and Song 2026,” Journal of Child Psychology and Psychiatry (2026), published online, https://doi.org/10.1111/jcpp.70167.
Certain air pollutants can produce free radicals and inflammatory cytokines that can penetrate the central nervous system and affect behavior. Long-term exposure to air pollution has been associated with a higher risk of developing ADHD.
There has, however, been little focus on the short-term effects of exposure. Might there be any correlation between levels of air contaminants and subsequent healthcare visits of adolescents for severe spikes in ADHD symptoms (frequently but not always associated with comorbid conduct disorder, oppositional defiance disorder, or mood disorder), such as extreme hyperactivity, serious rule violations, theft, or aggression to people or animals?
A South Korean (Republic of Korea) research team explored this question through a nationwide cohort study using the database of the National Health Insurance Service, a single-payer system, that covers the entire population.
Using a time-series approach, they compared measured levels of three airborne pollutants - particulate matter with a diameter ≤ 10 μm (PM10), nitrogen oxide (NO2), produced by vehicular traffic, and sulfur dioxide (SO2), produced by manufacturing industries- with healthcare visits with a principal diagnosis of ADHD. They chose these three contaminants because they have been associated with ADHD in long-term studies. What made this approach feasible is that healthcare visits are typically unscheduled in Korea, making it possible to get quick medical attention.
The team divided the country into sixteen regions, looked at boys and girls separately, and also split adolescents into two age groups (10 to 14 years and 15 to 19 years). They estimated region-specific daily concentrations of the three pollutants from 318 government-run monitoring sites, located according to population density and distribution.
The researchers next calculated zero(same day) to five-day lag figures for ADHD-related healthcare visits in each region and ran meta-analyses on the time-series data.
There were 7,200 ADHD-related healthcare visits in the 2013-2015 study period. Major increases in PM10 levels were associated with increased ADHD-related healthcare visits from the day of the spike to three days later, peaking the day after the upturn. Major increases in SO2 levels were associated with increased ADHD-related healthcare visits from one to four days later, peaking the day following the upturn. Major increases in NO2 levels were associated with increased ADHD-related healthcare visits from one to four days later, peaking three days after the spike.
There were no significant differences between male and female adolescents, and between younger and older adolescents.
The strongest increased risk for ADHD-related healthcare visits was for NO2 spikes (up 47 percent), followed by SO2 spikes (up 27 percent), with PM10 spikes coming in last (up 12 percent).
Among the limitations, the authors were unable to evaluate the most hazardous types of particulate emissions, because the smaller-diameter PM2.5 particles (≤2.5 μm) have only been measured partially in South Korea since 2015. On the other hand, they pointed out that this was the first study to investigate associations between short-term air pollution exposure and ADHD-related healthcare visits, and that it included all ADHD-related healthcare visits in South Korea, making the possibility of selection bias negligible. They recommended conducting similar studies on other national populations.
Proper development of the gut biota is important for the health of the brain and nervous system. It has been hypothesized that disturbances of gut bacteria by antibiotics could contribute to the development of neurodevelopmental disorders, including ADHD.
In the case of ADHD, studies to date have produced conflicting results. To tease out any familial confounding reflecting shared environment and genetics, a joint Dutch-Swedish team of researchers further tested the hypothesis through 7- to 12-year-old twins in the Netherlands Twin Register (25,781 twins) and 9-year-old twins in the Swedish Twin Registry (7,946 twins).
ADHD symptoms in the Netherlands cohort were derived from mothers' answers to the short Conners' Parental Rating Scale-Revised. For the Swedish cohort, ADHD was determined through the International Classification of Diseases codes for ADHD in the cross-linked National Patient Register.
Exposure to antibiotics during the first two years of childhood was determined by parent reports for the Netherlands twin cohort, and by prescription claims for antibiotics in the Swedish twin cohort.
Covariates were explored in both twin cohorts including educational attainment of parents, gender of the infant, birth weight, delivery mode, and asthma. Breastfeeding was also explored in the Dutch cohort.
In the unmatched analysis, comparing children with ADHD with non-related children without ADHD, early-life antibiotic use was associated with a significant 8% greater odds of ADHD in the Netherlands cohort and a significant 14% greater odds of ADHD in the Swedish cohort.
However, when limiting the analysis to matched monozygotic twins, the association disappeared altogether in both the Dutch and Swedish cohorts. Pooling both cohorts resulted in the same outcome. In all three cases, the odds flipped into a mildly negative association, but with no statistical significance.
Using higher cutoff values for ADHD symptoms made no difference.
The authors concluded, "In this large co-twin study performed in two countries, early-life antibiotic use was associated with increased risk of ADHD and ASD, but the results suggest that the association disappeared when controlled for shared familial environment and genetics, indicating that this association may be susceptible to confounding. Our results indicate that there is no association between ADHD and ASD diagnoses and early antibiotic use when environmental and genetic family factors are taken into account."
Claims-based real-world data can reveal population-level trends in health among people with neurodevelopmental disorders. This new study examined the prevalence, demographics, and chronic comorbidities of adults and of children and adolescents with ADHD in a large national health plan. It also compared healthcare use and costs between those with and without ADHD.
A research team in the United States conducted an observational cohort study using claims data from more than 1.9 million adults and nearly 500,000 children and adolescents, comparing individuals diagnosed with ADHD to those without the diagnosis.
ADHD was diagnosed in 4% of adults and in 5% of children and adolescents.
Comorbidities By The Numbers:
Disruptive childhood disorders are behavioral problems marked by ongoing defiance, uncooperativeness, and aggression that affect a child's daily life and relationships. The main types, oppositional defiant disorder (ODD) and conduct disorder (CD), involve persistent anger and argumentativeness in ODD, and more severe actions like aggression, cruelty, and criminal behavior in CD. Without treatment, these common childhood disorders can continue into adulthood and raise the risks of substance use, violence, incarceration, and early death.
Disruptive childhood disorders were twenty times more frequent among children and adolescents with ADHD than among those without ADHD diagnosis, and fifteen times more frequent among adults with ADHD.
Bipolar disorder was twelve times more common among children and adolescents with ADHD than those without ADHD, and seven times more common among adults with ADHD.
Schizophrenia was eleven times more prevalent among children and adolescents with ADHD than those without ADHD, and three-and-a-half times more common among adults with ADHD.
Anxiety was nine times more frequent among children and adolescents with ADHD than among those without ADHD diagnosis, and more than five times more frequent among adults with ADHD.
Depression was eight times more common among children and adolescents with ADHD than those without ADHD, and more than five times more common among adults with ADHD.
Suicidal ideation was eight times more prevalent, and suicide attempt seven times more prevalent, among children and adolescents with ADHD than those without ADHD. Both suicidal ideation and suicide attempt were five times more common among adults with ADHD.
Gender dysphoria was almost six times more frequent among children and adolescents with ADHD than among those without ADHD diagnosis, and five times more frequent among adults with ADHD.
Eating disorders were over four times more common among children and adolescents with ADHD than those without ADHD, and five times more common among adults with ADHD.
Substance-related disorders were over six times more prevalent, and alcohol use disorder was six times more prevalent among children and adolescents with ADHD than those without ADHD, and four and three times more prevalent among adults with ADHD.
Increased Costs of Medical Care:
These comorbidities and ADHD led to higher medical costs. Children and adolescents with ADHD spent $610 more annually on healthcare than those without, while adults with ADHD had $1,684 higher average yearly expenditures than non-ADHD adults.
The Take-Away:
This large claims-based analysis of a national commercial insurer found ADHD diagnoses in roughly 4% of adults and 5% of children. It documented substantially higher rates of co-occurring behavioral-health conditions and markedly greater healthcare utilization and expenditures among those with ADHD. The authors report increased odds for several co-occurring diagnoses, as well as higher per-member-per-month (PMPM) spending and per-thousand-per-month (PTPM) utilization, largely driven by greater use of behavioral health services.
Importantly, these results come from cross-sectional, claims data within a commercially insured population: they describe associations, not causal relationships, and may not generalize to uninsured, publicly insured, or otherwise different populations. These findings, therefore, warrant cautious interpretation and highlight the need for longitudinal and more representative studies to clarify drivers of the increased burden and to inform care and policy.
A landmark nationwide study from South Korea has uncovered a significant link between prenatal exposure to air pollution — specifically nitrogen dioxide (NO2) — and an increased risk of ADHD in children.
While researchers have long suspected that air pollutants interfere with fetal brain development through inflammation and oxidative stress, this study is one of the largest and most comprehensive of its kind, following nearly 1.5 million births for up to 13 years.
Why South Korea?
South Korea provided a unique countrywide “laboratory” for this research due to two key infrastructure strengths:
Key Findings: The “Smoking Gun” of NO2
While the study looked at several pollutants, nitrogen dioxide — a byproduct of fossil fuel combustion in cars and power plants — emerged as the primary concern.
Pollutant
Association with ADHD Risk
Nitrogen Dioxide (NO2)
Strongest Link: Every 1-ppb (part-per-billion) increase in exposure linked to a 22% rise in risk.
Sulfur Dioxide (SO2)
Minimal Link: Only a slight 4% increase per ppb.
Ozone (O3) carbon monoxide (CO), & particulates
No significant association was found.
The scale of the NO2 risk is particularly striking. Over the typical range of exposure levels found in the study (an interquartile range of 13 ppb), the data suggest a threefold increase in ADHD risk for children in the highest-exposure groups compared to the lowest.
Accounting for Other Factors
To ensure the results weren’t skewed by other variables, the researchers controlled for a wide range of confounders including:
The authors emphasized the strong association between maternal nitrogen dioxide exposure and ADHD, while also noting the small but significant association with sulfur dioxide.
The Take-Away: A New Frontier for Public Health
Historically, air quality laws have been designed to protect our lungs and hearts. However, this study adds to a growing body of evidence suggesting that the brain is likewise vulnerable.
In a commentary on the findings, expert George Ayoub argued that “neurodevelopment should be explicitly considered” when governments perform cost-benefit analyses on air quality regulation. My view is a bit different. The association is intriguing but the study does not establish cause and effect. Many statistically significant environmental risk associations for neurodevelopmental disorders have disappeared after controlling for maternal risk for ADHD. I hope this research team will do those analyses if feasible.
Executive functions (EFs) are the cognitive control systems that allow people to pursue goals, make decisions, and adapt to changing circumstances. Researchers generally break them into three overlapping capacities: working memory (holding and manipulating information in mind), inhibitory control (suppressing impulses and filtering out distractions), and cognitive flexibility (switching between tasks or mental frameworks). Strong EFs in childhood predict academic achievement, social competence, and long-term mental health; weaknesses in these areas that go unaddressed can persist into adulthood, undermining school performance, career prospects, and well-being.
The Background:
Interest in training these skills has grown rapidly, but most research has been conducted in Western settings. China presents a distinctive context. Collectivist values make group-based programs culturally natural, and parental investment in academic outcomes is high. Both of these factors should, in theory, work in an intervention’s favor. At the same time, tightly scheduled school days (sessions typically capped at 30 minutes or less) constrain what is actually deliverable. A growing number of randomized controlled trials (RCTs) have tested EF interventions with Chinese children, but until now, no one has pulled that evidence together systematically.
The Study:
A new network meta-analysis did exactly that. The researchers screened RCTs involving Chinese children aged 3–12, including both typically developing children and those showing subclinical signs of ADHD or autism spectrum disorder (ASD), for instance, siblings of children with an ASD diagnosis. Children who already carried a formal neurodevelopmental diagnosis were excluded. Fifty-two trials covering nearly 3,000 children met the inclusion criteria. Interventions fell into four categories:
The headline finding is that three of the four intervention types produced statistically significant improvements across all three EF domains. The exception was the hybrid physical-cognitive program, which did not reach significance for inhibitory control. Positive results across the board might sound encouraging until you look at the actual effect sizes.
The Results:
The actual effects were negligible. Every significant result fell well below what methodologists define as a “small” effect (a standardized mean difference, or SMD, of 0.2). The largest effect size in the entire analysis was an SMD of 0.097 (less than half that threshold). The authors summarize the interventions’ effects as “modest,” but that is generous phrasing for numbers that, in practical terms, amount to very little. The analysis also showed signs of publication bias, meaning that studies with null or negative results may not have been published, potentially inflating even these modest figures.
The Take-Away:
It is important to note that these results don’t necessarily mean that this is the last word on EF training. The results apply specifically to Chinese children working within the time constraints of Chinese school schedules, and they exclude children with diagnosed ADHD, a population for whom cognitive interventions sometimes show larger effects. Generalizing beyond those boundaries is unwarranted.
What the findings do suggest is that structured EF programs, as currently implemented in Chinese educational settings, are not delivering meaningful real-world benefits. Statistical significance, it is worth remembering, is not the same as practical significance, and the gap between the two is sharp here.
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Language is powerful. The words we choose not only reflect our understanding of the world but also actively shape it. Recently, this truth has been at the center of a growing debate in the mental health field regarding how we talk about ADHD.
In a recent paper published in The Lancet Psychiatry titled “The Power of Words: Respectful Language in ADHD Research,” French and colleagues advocated for a shift toward "neurodiversity-affirmative language”. Rooted in the social model of disability, their proposal encourages researchers to abandon traditional medical terminology, e.g., words like disorder and deficit, in favor of more neutral terms such as condition and challenge.
My colleague, Dr. Michael Miller, and I read this with great interest. We completely agree that revising language is essential to good science and that, both as researchers and as human beings, we are ethically bound to speak respectfully. However, we felt compelled to write a response. In our new paper, we argue that while language must evolve, it must do so scientifically.
The Two Prerequisites for Language Change
If we are going to fundamentally shift our scientific lexicon, two requirements must be met:
Currently, the proposal by French and colleagues meets neither requirement. While they claim consensus is accumulating that certain terms are disrespectful, they provide zero empirical evidence that this view is shared by the community of individuals living with ADHD. Even proponents of patient-centered language admit there is surprisingly little data supporting specific language changes.
More alarmingly, the recommended changes severely dilute the scientific accuracy of our field. Let’s look at two examples.
Why a "Deficit" is Not Just a “Challenge"
French and colleagues suggest replacing the term deficit with challenge. On the surface, challenge sounds softer and more affirming. But scientifically, these words are not interchangeable.
For decades, the term deficit has been defined by a specific performance metric that falls substantially below an expected level. It is a measurable reality. A challenge, on the other hand, refers to a new or difficult task that tests someone's ability.
Every single human being is "challenged" by complex neuropsychological tests, but only some individuals who face that challenge demonstrate scientifically significant deficits. If we relabel measurable deficits as universal challenges, we sacrifice the exactness required to communicate scientific findings and accurately measure the effects of life-changing treatments.
ADHD is a Disorder, Not Just a "Condition"
Another proposal is to replace the word disorder with condition.
In mainstream psychiatry, a disorder is a clinically significant disturbance that causes distress or disability. The word purposefully separates natural human variation from the suffering (pathos) that gives pathology its meaning.
Condition is a completely neutral term. Pregnancy is a condition. Being tall is a condition. Calling ADHD a condition distances the diagnosis from the profound suffering it can cause.
French et al. argue against framing ADHD as a disorder because it exists on a spectrum without a clear cutoff, its manifestation is context-dependent, and its definition evolves. But if we apply that logic across all of medicine, the concept of disease unravels:
The Real-World Danger of Imprecise Language
This is not merely an academic debate over semantics. The language we use has real-world implications. In the United States and across the globe, our healthcare, educational, and legal systems run on precise medical language. Terms like impairment, dysfunction, and disorder are legally and administratively required to justify support services, workplace accommodations, specialized educational therapies, and medications. The language of pathology in diagnostic manuals regulates the flow of these resources.
If we reclassify ADHD as a neutral condition characterized only by challenges, we risk erecting massive bureaucratic barriers. Imprecise language could easily be used by institutions or insurance companies to deny vital care to the people who need it most.
The Need for Lexical Discipline
Attempting to characterize a clinical disorder entirely through its strengths happens in a scientific vacuum. We cannot ignore the vast body of rigorous evidence confirming that ADHD meets the long-standing criteria used by mental health science to identify clinical disorders.
As professionals, our respect for the ADHD community demands a commitment to language that is clear, correct, and evidence-based. To build genuine consensus about how we talk about ADHD, we need meaningful, collaborative dialogue that integrates compelling empirical data and rigorous theory.
This standard of "lexical discipline" is not just a technical preference. It is a vital mechanism through which science and the mental health professions uphold their duty to society.
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