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A new study suggests that children and teenagers diagnosed with attention-deficit/hyperactivity disorder (ADHD) or autism spectrum disorder (ASD) in Denmark now more closely resemble the general population than those diagnosed a decade ago.
The study, led by the Barcelona Institute for Global Health (ISGlobal) and Aarhus University, suggests that changes in who is being identified and diagnosed may have contributed to the rise in ADHD and ASD diagnoses.
The findings were published in JAMA Psychiatry.
Researchers analyzed data on more than 2.1 million children and adolescents in Denmark. They compared more than 71,000 young people diagnosed with ADHD or ASD between 2012 and 2022 with more than 713,000 who had neither diagnosis.
Children diagnosed with ADHD or ASD were still more likely to have several characteristics previously associated with the conditions. However, the differences between them and the wider population became smaller over the 10-year period.
For example, children born with low birth weight were 54 per cent more likely to later receive an ADHD or ASD diagnosis at the beginning of the study period. By the end, the difference had fallen to 17 per cent.
Similar declines were found in links with premature birth and several measures of socioeconomic disadvantage.
“The key message is not that these risk factors are no longer important,” said Magnus Elias Tarp, a PhD student at Aarhus University and the study’s first author.
“What we found is that people diagnosed in recent years resemble the general population more closely than those who received the same diagnoses a decade ago.”
Changing diagnosis patterns
The researchers said greater awareness of ADHD and ASD, improved identification by healthcare and education systems, wider access to diagnostic assessments and changes in how neurodevelopmental conditions are recognized could have contributed to the shift.
However, the study could not determine how much each factor contributed.
The researchers said the findings indicate that rising diagnosis rates should not automatically be interpreted as evidence that the underlying occurrence of ADHD or ASD has increased by the same amount.
“Our findings help us better understand why ADHD and autism diagnoses have increased so markedly in recent years,” said Oleguer Plana-Ripoll, a researcher at ISGlobal and Aarhus University and the study’s senior author.
He said the findings do not show that ADHD or autism is being overdiagnosed or has become less severe. Instead, they suggest that the population receiving these diagnoses has changed over time.
Further research in other countries will be needed to determine whether the findings can be replicated elsewhere.
