Study reveals narrowing gaps between diagnosed and peer children with ADHD and autism in Denmark over a decade

A Danish study shows children with ADHD and autism now more closely resemble their peers than a decade ago, suggesting changing diagnostic practices rather than an increase in severity or prevalence.

Children and adolescents in Denmark diagnosed with attention-deficit/hyperactivity disorder or autism spectrum disorder now look more like their peers in the general population than those given the same diagnoses 10 years ago, according to a study led by the Barcelona Institute for Global Health and Aarhus University and published in JAMA Psychiatry. The researchers say the pattern suggests that rising diagnosis rates may reflect not only the conditions themselves, but also changes in who is being identified.

The team analysed data from more than 2.1 million Danish children and teenagers, comparing more than 71,000 people diagnosed with ADHD or autism between 2012 and 2022 with more than 713,000 matched peers without those diagnoses. They found that children with ADHD or autism were still more likely to have features long linked to neurodevelopmental disorders, including preterm birth, low birthweight, lower parental education and income, and a family history of psychiatric illness. But the gaps narrowed steadily over the decade.

One example was low birthweight. At the start of the study period, children born at a low weight were 54% more likely to later receive an ADHD or autism diagnosis than children born at a normal weight. By the end of the period, that difference had fallen to 17%. Similar declines were seen for preterm birth and several measures of socioeconomic disadvantage. Magnus Elias Tarp, the study’s first author, said the point was not that these factors no longer matter, but that recently diagnosed people resemble the wider population more closely than earlier groups did.

The findings fit with broader Danish research showing how quickly diagnosis rates have risen. According to University of Copenhagen work cited in the reports, ADHD diagnoses increased from about 0.1% of the population in 2000 to more than 3% by 2022, while autism prevalence has also climbed sharply across birth cohorts. Researchers say the change may reflect wider diagnostic criteria, greater awareness, improved access to assessment and more contact with health and education services, rather than a simple rise in underlying risk. The authors cautioned that the study does not prove overdiagnosis or a change in severity, but it does suggest that trends in prevalence must be read alongside changing diagnostic practice.