Changes in incidence of hospital diagnoses of mental disorders among children and adolescents over the past 3 decades.

BACKGROUND: WHO considers mental disorders a significant disease burden among children and adolescents. However, there is a lack of population-based studies on the time trends of mental disorder diagnosis in this group. OBJECTIVE: To investigate changes in the incidence of clinical diagnoses of mental disorders among all Danish children and adolescents in the past 3 decades. METHODS: In this retrospective cohort study, we included all Danish-born individuals from 1976. Follow-up started in 1994 until first diagnosis of a mental disorder, 18th birthday, emigration from Denmark, death or end of study on 30 June 2023. Sex-specific cumulative incidences of diagnosis by age 18 were calculated in 5-year birth cohorts from 1976-1980 to 2001-2005 using the Kaplan-Meier estimator. Poisson regression was used to estimate the age-specific and sex-specific incidence rates. FINDINGS: From 1994 to 2023, a total of 193 354 children and adolescents received a mental disorder diagnosis. Over 3 decades the cumulative incidence of any mental disorder diagnosis before age 18 increased from 1.46% (95% CI 1.40% to 1.52%) to 14.56% (95% CI 14.36% to 14.76%) among females and from 1.22% (95% CI 1.16% to 1.27%) to 14.77% (95% CI 14.57% to 14.96%) among males. A lower mean age at first diagnosis accounted for an estimated 15-22% of the observed incidence in the most recent years. CONCLUSIONS: This study demonstrates a large increase in mental disorder diagnoses. Observed rates were in part accounted for by decreasing age at first diagnosis. While some of the remaining increase may reflect a true rise in the underlying prevalence of mental disorders, changes in diagnostic practice and greater awareness of mental disorders are probable contributors. CLINICAL IMPLICATIONS: Estimates of specific diagnostic rates are essential for appropriate healthcare planning and resource allocation to accommodate the increasing number of mental disorder diagnoses among children and adolescents.