The cumulative incidence rate for any mental disorder at age 18 years is 11.02%, suggesting that many mental disorders develop during childhood and adolescence, according to the results of a comprehensive Danish population study published in the Journal of Clinical Psychiatry.
Researchers analyzed data from nationwide Danish registries on the entire cohort of children born in 1995, with follow-up to December 31, 2013. Those who migrated during this period were censored from the analyses. Researchers aimed to establish the total number of all first occurrences of diagnosed mental disorders that emerged in childhood and adolescence.
Ten major categories of mental disorders were calculated for 67,347 children (51.4% boys). The incidences of any mental disorder, substance use disorder, depression, and anxiety disorders increased during adolescence. In contrast, the incidences of autism spectrum disorders, attention-deficit/hyperactivity disorder (ADHD), and tic disorder rose during childhood, but declined afterward. The incidence rates of substance use disorders, autism spectrum disorders, ADHD, conduct disorder, and tic disorder were higher in boys, whereas girls were at greater risk for depressive, anxiety, obsessive-compulsive, and eating disorders.
Although the cumulative incidence rate at age 18 years was 11.02% for any mental disorder, the highest rate for an individual disorder was 2.51% for ADHD. Depression had an incidence rate of 1.84%, autism spectrum disorders a rate of 1.79%, conduct disorder a rate of 1.32%, and substance use disorders a rate of 1.02%. Rates of all other diagnoses were less than 1%.
The researchers noted a number of protective risk factors, including female sex, higher parental education level, higher socioeconomic status, and greater disposable family income. Risk factors that predicted mental disorders included perinatal risks, social position during childhood or adolescence, parental divorce, parental history of mental illness before the diagnosis of the child, paternal death, and the child’s being placed outside the home. They added that the increasing incidences of some disorders and decreases in others may reflect brain maturation effects and changes in neural systems that are involved in higher cognitive functions, reasoning, social interactions, cognitive control of emotions, risk-vs-reward appraisal, and motivation.
The use of a single national population for this study may limit the generalizability of its results.
“At the end of adolescence before turning into adulthood, 11 in 100 individuals had been diagnosed with a mental disorder in this cohort,” the researchers wrote. They advocated for the need to provide treatment facilities and continuous care for various disorders at all developmental stages.
Steinhausen H-C, Jakobsen H. Incidence rate of treated mental disorders in childhood and adolescence in a complete nationwide birth cohort. J Clin Psychiatry. 2019;80:17m12012.