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Disease and treatment

How many children and adolescents in Denmark have been diagnosed with a mental disorder?

Fifteen percent of Danish children are diagnosed with a mental disorder before 18 years of age. Anxiety is the most frequent mental disorder among girls and ADHD among boys.

A new Danish study reveals that 15% of children in Denmark born between 1995 and 2016 have been diagnosed with a mental disorder before 18 years of age.

In all, 41,350 girls (14.6%) and 58,578 boys (15.5%) have been diagnosed with a mental disorder.

The types of diagnoses boys and girls receive and when they are diagnosed differ. The findings were published recently in JAMA Psychiatry.

“Detailed knowledge about the epidemiology of mental disorders among children and adolescents has been lacking. We simply know too little about fundamental things such as the occurrence of the individual disorders, at which ages the various disorders are first diagnosed and the gender differences in these patterns. Our study is the first to provide a detailed picture of the underlying epidemiology of mental disorders among children and adolescents,” explains Søren Dalsgaard, specialist physician in child and adolescent psychiatry and Professor, Department of Economics and Business Economics, Aarhus University.

Soren Dalsgaard led the study, which was carried out in collaboration with other researchers from the National Centre for Register-based Research at Aarhus University.

Anxiety predominates among girls and ADHD among boys

The study included 1.3 million children. The researchers used data from the Danish National Patient Registry, the Danish Psychiatric Central Research Registry and other registries to examine how many children in Denmark born between 1995 and 2016 had been diagnosed with a mental disorder.

They also examined which diagnoses the children had received and when they had been diagnosed.

The study revealed the following.

• The most frequently diagnosed mental disorder among girls was anxiety: 7.9%.

• The most frequently diagnosed mental disorder among boys was ADHD (attention-deficit/hyperactivity disorder): 5.9%.

• Neurodevelopmental disorders, such as ADHD and autism spectrum disorders, which by definition develop in early childhood, were diagnosed significantly earlier among boys than among girls. For ADHD, most boys were diagnosed at age 8 years and girls at age 17 years.

• This also applied to autism: boys were typically diagnosed when they were 4–13 years old and girls at 12–17 years old.

“Girls being diagnosed so late is noteworthy, since they must have exhibited autistic behaviour before 3 years of age. Many girls reach about 15 years of age before receiving the correct diagnosis, and this is not good enough,” says Søren Dalsgaard.

Girls are not diagnosed early enough In Denmark

Søren Dalsgaard believes that Denmark is generally not good enough at detecting whether girls have ADHD or autism spectrum disorders that need to be addressed.

The problem is that girls who are diagnosed late do not receive the necessary help early enough, and this can lead to even greater difficulties later in life.

“Efforts have not targeted girls to the same degree as boys, and that is not good, because the girls may then have problems throughout their school years before being diagnosed. We have shown in several studies that girls with ADHD have higher relative risks of drug addiction, depression and psychoses than boys with ADHD. One explanation may be that they did not receive any help for their ADHD difficulties when they were younger,” says Søren Dalsgaard.

Surprising discovery about schizophrenia

The researchers also found that early-onset schizophrenia, a rare disorder in which schizophrenia develops before 18 years of age, is more common among girls than boys.

This contrasts with the prevailing clinical consensus that schizophrenia is slightly more frequent among boys than girls, similar to schizophrenia in adulthood, which is by far more frequent.

In fact, the opposite is true, at least for those born between 1995 and 2016: almost twice as many girls (0.76%) as boys (0.48%) have been diagnosed with a schizophrenia spectrum disorder before 18 years of age.

“This is a completely new finding, and we do not know why. This is striking, also because some of the other mental disorders are detected late,” says Søren Dalsgaard.

The proportion of young people with mental disorders is similar to that in other countries

What is the significance of 15% of children and adolescents in Denmark being diagnosed with a mental disorder?

According to Søren Dalsgaard, this percentage is similar to what has been found worldwide, including the results of a meta-analysis of 41 studies from 27 countries.

There is therefore no indication that children and adolescents are being overdiagnosed in Denmark, and Søren Dalsgaard believes that the figures mostly indicate that Denmark is good at identifying the children who have difficulties.

“This is the most important thing for me, and, for example, the fact that Denmark is good at identifying the girls with anxiety is both good and important so that we can help them further,” he explains.

Improving the detection of children and adolescents with problems

Søren Dalsgaard thinks that these research results should be used to focus on how mental health services can improve so that they not only identify all children with mental health problems but also discover them as early as possible.

This applies especially to girls with ADHD, autism and other neurodevelopmental disorders.

According to Søren Dalsgaard, the people attempting to detect the girls who are at risk of receiving a diagnosis and especially a late diagnosis of a mental disorder need to be aware of social inequality.

In a previous study, for example, Kathrine Bang Madsen, Postdoctoral Fellow, Aarhus University showed that the probability of a child who fulfilled the diagnostic criteria for ADHD was actually diagnosed and received the necessary help was significantly lower if the child was from a disadvantaged family with low income and low education and if the child was a girl.

“We have become much better at identifying the right children and adolescents than 20 years ago, and today they are receiving better treatment than they did in the past, but there is room for improvement. The study especially indicates these areas,” says Søren Dalsgaard.

“Incidence rates and cumulative incidences of the full spectrum of diagnosed mental disorders in childhood and adolescence” has been published in JAMA Psychiatry. In 2016, the Novo Nordisk Foundation awarded Søren Dalsgaard a grant for the project Polygenic Risk Scores and Early Social Adversities in Predicting the Developmental Course and Trajectory in Individuals with ADHD.

Incidence rates and cumulative incidences of the full spectrum of diagnosed mental disorders in childhood and adolescence” has been published in JAMA Psychiatry. In 2016, the Novo Nordisk Foundation awarded Søren Dalsgaard a grant for the project Polygenic Risk Scores and Early Social Adversities in Predicting the Developmental Course and Trajectory in Individuals with ADHD.

Søren Dalsgaard
MD, Professor, Senior Researcher
CIRRAU provides the necessary and fundamental data infrastructure to support and conduct a large variety of register-based research projects ranging from intervention studies of vulnerable children and adolescents, through population-based genetic studies of mental disorders to nationwide population-based studies of a large variety of exposures, outcomes and consequences of outcomes. This project database is one of the world’s most comprehensive datasets in its combination of nationwide individual level information on health, firms and companies, family factors, social and contextual information, and it is further enriched with genetic information for 80,000 Danes. CIRRAU provides a data solution that constitutes the foundation for register-based analyses carried out in scientific programs supported financially by the Lundbeck Foundation, TrygFonden, EU, The Stanley Medical Research Institute, The Simon Foundation and NordForsk. So far, CIRRAU has provided fundamental data-infrastructure for research projects attracting well above DKK 300 million and supported research projects leading to more than 130 papers in scientific peer-reviewed journals. Many of these papers were published in some of the most high-ranking scientific journals. These include Science, Nature, The Lancet, Epidemiology, Biological Psychiatry, Human Reproduction, JAMA Psychiatry, Journal of Applied Econometrics, Journal of Health Economics, and Social Science and Medicine.