Incidence of Mental Illness in Youth Hovers Around 15%

By age 18, approximately 15% of the cohort had been diagnosed with a mental disorder.

A Danish nationwide cohort study published in JAMA Psychiatry found a significant burden of mental illness in children and adolescents. By the age of 18 years, approximately 15% of the cohort had been diagnosed with a mental disorder. 

Søren Dalsgaard, MD, PhD, at the National Center for Register-Based Research at Aarhus University in Denmark, led study efforts to quantify the burden of mental disorders in Danish youth. This cohort study included all individuals born in Denmark from January 1, 1995 through December 31, 2016 (N=1.3 million) based on Danish Civil Registration System data. Cohort members were followed-up from birth through December 31, 2016, with demographic and clinical information abstracted from the Danish Psychiatric Central Research Register and the Danish National Patient Register.

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The outcome of interest was the diagnosis of a mental disorder before age 18 years per the ICD-10 Classification of Mental and Behavioral Disorders: Diagnostic Criteria for Research. Sex- and age-specific incidence rates were calculated as incident cases per 10,000 person-years. Cumulative incidences, defined as the probability of the disorder per 100 cohort enrollees, were calculated for each psychiatric disorder.

A total of 1.3 million children contributed data to analyses, for 14 million person-years of observation. Overall, 99,926 individuals (15.01%) received a diagnosis of a mental disorder before 18 years of age. The disease with the highest cumulative incidence in girls was anxiety disorder (7.85%), and in boys the most common disease was attention-deficit/hyperactivity disorder (ADHD) (5.90%).

In girls compared with boys, the cumulative incidence was higher for schizophrenia (0.76% vs 0.48%), mood disorders (2.54% vs 1.10%), depression (2.41% vs 0.92%), anxiety (7.85% vs 4.58%), obsessive-compulsive disorder (0.96% vs 0.63%), eating disorders (1.80% vs 0.28%), and personality disorders (1.05% vs 0.30%). However, boys had a higher risk for intellectual disability (1.52% vs 0.88%), autism spectrum disorders (4.26% vs 1.77%), other developmental disorders (2.74% vs 1.41%), ADHD (5.90% vs 3.04%), oppositional defiant disorder/conduct disorder (1.28% vs 0.46%), attachment disorders (0.71% vs 0.52%), and tic disorders (1.36% vs 0.42%).

The overall risk for diagnosis of a mental disorder before age 6 years was 2.13% and was higher in boys (2.78%) compared with girls (1.45%). The risk for diagnosis prior to age 13 years was also higher in boys vs girls (10.23% vs 5.17%). Peak incidence occurred earlier in boys vs girls for ADHD (8 vs 17 years), intellectual disability (5 vs 14 years), and other developmental disorders (5 vs 16 years).

These data underscore the significant burden of mental illness in children and adolescents. As a study limitation, investigators noted that in using a register to collect data, children who did not seek treatment would be excluded from analyses; thus, some risks may have been underestimated.

The between-gender differences in age at peak incidence for intellectual disabilities may indicate delayed detection in girls. “The distinct signatures of the different mental disorders with respect to sex and age may have important implications for service planning and etiological research,” the investigators wrote.

Disclosure: One study author declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures


Dalsgaard S, Thorsteinsson E, Trabjerg BB, et al. Incidence rates and cumulative incidences of the full spectrum of diagnosed mental disorders in childhood and adolescence [published online November 20, 2019]. JAMA Psychiatry. doi:10.1001/jamapsychiatry.2019.3523