ADHD and autism diagnoses now capture broader population, Danish study finds

Over the past decade, the children and adolescents receiving diagnoses of ADHD or autism in Denmark have begun to look less like a distinct clinical population and more like the general population around them. A study of more than 2.1 million Danish children, comparing roughly 71,000 diagnosed with attention-deficit/hyperactivity disorder or autism spectrum disorder between 2012 and 2022 against 713,000 peers without these diagnoses, found that the gap between the two groups has narrowed substantially. The research, published in JAMA Psychiatry and led by the Barcelona Institute for Global Health and Aarhus University, suggests that the rising tide of diagnoses over the past decade may reflect not simply more children developing these conditions, but rather a shift in who is being identified and labeled.

For years, researchers have documented that certain markers cluster more heavily among people diagnosed with ADHD or autism than among the general population. Children born prematurely or at low birth weight, those from households with lower parental education or income, those with a family history of psychiatric illness, and those who used healthcare services frequently before diagnosis—these profiles have long been overrepresented in diagnostic populations. The Danish researchers set out to ask whether this profile itself had changed. What they found was striking: the characteristics that once clearly distinguished diagnosed children from their peers have become progressively less distinctive.

The most dramatic shift involved birth weight. A decade ago, children born with low birth weight were 54 percent more likely to receive an ADHD or autism diagnosis than those born at normal weight. By 2022, that gap had shrunk to 17 percent. Similar reductions appeared across other markers—preterm birth, socioeconomic disadvantage indicators—all moving in the same direction. The diagnosed population was becoming more representative of the broader childhood population.

Magnus Elias Tarp, the study's first author and a PhD student at Aarhus University, was careful to clarify what this pattern does and does not mean. "The key message is not that these risk factors are no longer important," he said. Rather, the finding is that people receiving diagnoses in recent years resemble the general population more closely than those diagnosed ten years earlier. The study cannot pinpoint why this shift has occurred, but the researchers point to several plausible explanations: greater public awareness of ADHD and autism, improved identification by schools and healthcare providers, broader access to diagnostic assessment, or a lowering of the threshold at which neurodevelopmental traits are considered clinically significant enough to warrant a diagnosis.

This reframing matters for how we interpret the headline numbers. The rise in ADHD and autism diagnoses has been substantial and consistent across many countries. But the Danish data suggest that this increase should not be read simply as evidence that more children are developing these conditions. Instead, it may reflect a widening of the diagnostic net—a shift toward capturing individuals who would not have been identified as having these conditions under older, narrower criteria. Oleguer Plana-Ripoll, senior author and researcher at both ISGlobal and Aarhus University, emphasized that the findings do not indicate overdiagnosis or that these conditions have become less severe. Rather, the population receiving diagnoses has changed, and this distinction is crucial for interpreting current trends.

The implications ripple outward. When researchers report improvements in outcomes for people with ADHD or autism, some of that apparent progress may actually reflect the fact that the diagnosed population now includes individuals with milder presentations or fewer complicating factors—not necessarily that the conditions themselves have become more treatable. Healthcare systems, schools, and social services planning for the needs of children with these diagnoses must account for this shifting profile. The researchers note that similar studies in other countries would be needed to determine whether Denmark's pattern holds elsewhere, leaving open the question of whether this represents a global shift or a phenomenon specific to the Danish healthcare and educational context.