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April 23, 2021
With the growth of the Internet, we are flooded with information about attention deficit hyperactivity disorder from many sources, most of which aim to provide useful and compelling "facts" about the disorder. But, for the cautious reader, separating fact from opinion can be difficult when writers have not spelled out how they have come to decide that the information they present is factual.
My blog has several guidelines to reassure readers that the information they read about ADHD is up-to-date and dependable. They are as follows:
Nearly all the information presented is based on peer-reviewed publications in the scientific literature about ADHD. "Peer-reviewed" means that other scientists read the article and made suggestions for changes and approved that it was of sufficient quality for publication. I say "nearly all" because in some cases I've used books or other information published by colleagues who have a reputation for high-quality science.
When expressing certainty about putative facts, I am guided by the principles of evidence-based medicine, which recognizes that the degree to which we can be certain about the truth of scientific statements depends on several features of the scientific papers used to justify the statements, such as the number of studies available and the quality of the individual studies. For example, compare these two types of studies. One study gives drug X to 10 ADHD patients and reported that 7 improved. Another gave drug Y to 100 patients and a placebo to 100 other patients and used statistics to show that the rate of improvement was significantly greater in the drug-treated group. The second study is much better and much larger, so we should be more confident in its conclusions. The rules of evidence are fairly complex and can be viewed at the Oxford Center for Evidenced Based Medicine (OCEBM;http://www.cebm.net/).
The evidenced-based approach incorporates two types of information: a) the quality of the evidence and b) the magnitude of the treatment effect. The OCEBM levels of evidence quality are defined as follows (higher numbers are better:
Non-randomized, controlled studies. In these studies, the treatment group is compared to a group that receives a placebo treatment, which is a fake treatment not expected to work.
It is possible to have high-quality evidence proving that a treatment works but the treatment might not work very well. So it is important to consider the magnitude of the treatment effect, also called the "effect size" by statisticians. For ADHD, it is easiest to think about ranking treatments on a ten-point scale. The stimulant medications have a quality rating of 5 and also have the strongest magnitude of effect, about 9 or 10.Omega-3 fatty acid supplementation 'works' with a quality rating of 5, but the score for the magnitude of the effect is only 2, so it doesn't work very well. We have to take into account patient or parent preferences, comorbid conditions, prior response to treatment, and other issues when choosing a treatment for a specific patient, but we can only use an evidence-based approach when deciding which treatments are well-supported as helpful for a disorder.
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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