Denmark study suggests broader diagnostic criteria may explain rise in ADHD and autism diagnoses

Research in Denmark indicates that increasing diagnoses of ADHD and autism may reflect changes in patient profiles, awareness, and detection methods rather than an actual rise in prevalence, reshaping understanding of these neurodevelopmental conditions.

Researchers in Denmark say rising diagnoses of ADHD and autism may reflect a changing patient population as much as a changing disease burden. A study in JAMA Psychiatry found that children and adolescents given these diagnoses between 2012 and 2022 increasingly looked like the wider population in their birth histories, family backgrounds and other measured traits. That suggests the trend cannot be read simply as proof that the conditions are becoming more common. According to the study, the shift may also reflect greater awareness, stronger detection by health and education services, wider access to assessments and possible changes in the threshold for diagnosis.

The research team, led by Aarhus University and the Barcelona Institute for Global Health, examined data on more than 2.1 million children and adolescents in Denmark. They compared more than 71,000 people diagnosed with ADHD or autism with more than 713,000 peers without either condition. The authors found that characteristics previously linked more strongly with later diagnosis, including preterm birth, low birth weight, lower parental education and household income, parental psychiatric history and heavier healthcare use before diagnosis, were still associated with ADHD and autism. But those differences narrowed over the decade studied.

One of the clearest changes involved birth weight. At the start of the study period, children born with low birth weight were 54% more likely than those born at normal weight to later receive an ADHD or autism diagnosis. By the end of the period, that figure had fallen to 17%. Similar declines were seen for preterm birth and several markers of social disadvantage, suggesting that the profile of those being diagnosed has broadened over time. The researchers said this does not mean the risk factors no longer matter, but that they are less useful on their own for understanding who is now being identified.

Oleguer Plana-Ripoll, the study’s senior author, said the findings help explain why diagnoses have risen so sharply in recent years, while not proving that ADHD and autism are being overdiagnosed or that the conditions are less severe. Magnus Elias Tarp, the study’s first author, said the central point was that more recent patients resemble the general population more closely than those diagnosed a decade ago. The authors said that matters for health, education and social planning, and could also help explain why some recent studies have reported better outcomes: part of that improvement may reflect who is being diagnosed now, rather than a change in the natural course of the conditions.