Age and sex specific incidence for depression from early childhood to adolescence: A 13-year longitudinal analysis of German health insurance data
Introduction
While some 50 years ago, the general opinion was that childhood depression did not occur, and that in adolescence such symptoms are merely an expression of normal adolescent development, there is no longer any doubt that depressive disorders already occur in childhood and adolescence. In fact, depression is the worldwide leading cause of disability among children and adolescents, and is a public health challenge because of its major impact on quality of life and academic and school related development (Bettge et al., 2008). As defined in the ICD-10 and DSM-5, a Major Depressive Disorder (MDD) is a mental illness mainly characterized by at least two weeks of depressed mood, diminished interest or pleasure and fatigue or loss of energy. Numerous other symptoms can occur, such as vegetative symptoms with sleep disorders and loss of appetite, as well as feelings of insufficiency and guilt leading up to suicidality. More so, depression is a relevant risk factor for suicide, which is the second-to-third leading cause of death among teenagers in the US (Shain, 2016; Windfuhr et al., 2008). Furthermore, approximately 60% of depressed youths report having suicidal thoughts, and 30% attempt suicide (Merikangas et al., 2010; Posner et al., 2007). In a recent national representative survey in the US, the 12-month prevalence of a Major Depressive Disorder (MDD) among 13 to 18-year-olds was 7.8% (Avenevoli et al., 2015). Even in preschool children, the prevalence rate was about 2% and rose up to 5–6% when a high symptom load with depressive symptoms were used for estimating prevalence (Egger and Angold, 2006; Fuhrmann et al., 2014; Wichstrøm et al., 2012).
An essential and in many respects unexplained phenomenon is the disproportionate increase of incidence among adolescent girls compared with boys despite the approximate balance of the prepubertal sex ratio. Numerous epidemiological studies indicate this divergence of incidence between 13 and 15 years of age (Angold et al., 1998; Wade et al., 2002). There are also findings - most recently from a meta-analysis by Salk et al. (2017) - which identify a significantly increased incidence among girls already at 12 years of age. Notably, there is convincing evidence that this sex difference is not primarily an age effect, but more so an effect of the puberty development. Indeed, Angold et al. (1998) found that the morphological signs of puberty are correlated with the sex difference of depression incidence. In particular, an early onset of puberty seems to be a risk factor for depression among girls (Angold et al., 1998; Galvao et al., 2014; Hamilton et al., 2014; Negriff and Susman, 2011).
Another frequently discussed question is whether early onset (defined differently in different studies; often classified as beginning between the ages of 14 and 17 (Wilson et al., 2015)) of depression is a high-risk factor for relapse and a risk factor for comorbid disorders. Many findings indicate that an early onset is associated with psychiatric co-morbidity, greater psychosocial impairment and physical health problems (Wilson et al., 2015). There is also strong evidence that early onset is associated with recurrent MDD (Wilson et al., 2014). Nevertheless, little is known about a potentially relevant sex difference in terms of an early or prepubertal depression onset and the further course.
This raises two central research questions: I) Is the incidence of depressive disorders in children and adolescents related to age and sex? II) Does prepubertal depression diagnosis impact the risk of depression in early and late adolescence and does the risk differ between boys and girls? In order to address these questions, large representative samples are needed. Therefore, we investigated a cohort of children from 6 to 18 years of age longitudinally, over the course of 13 years.
Section snippets
Data source and study population
Data were provided by the Barmer Health Insurance, one of the major health insurers in Germany, covering approximately 10% of the German population. In Germany, nearly everybody has some kind of health insurance, with more than 85% of the German population insured in statutory health insurances (Grobe et al., 2017). Barmer clients are similar to all patients with statutory health insurance in Germany regarding the level of education, BMI, and proportion of individuals with a poor health Status (
Results
The total population of continuously Barmer insured children from 2005 to 2017 based on the birth cohort of 1999 was 61,199 children/adolescents, the proportion of males was 50.6%. The median number of depression related physician contacts for all incident cases was two.
Sex and age-difference for incidence of depression from 6 to 18 years of age
This study provides insight from one of the biggest German health insurance data sets about the incidence of childhood depression. It appears that the sex difference occurs at 13 years of age. The steep incidence increase in girls results in a threefold higher incidence among girls compared to boys at the age of 15. The results presented here correspond with findings of other reviews and studies including a large scaled Danish population-based cohort study, which indicates an emerging sex
Conclusion
In summary, our finding, indicating sex and age specific incidence of depressive disorders with a steep increase in the incidence among females from 13 years of age adds to the results of other population-based studies, with subtle differences likely explainable by secular trends in age at puberty and national differences in pubertal timing. Our unique finding is that the diagnosis of depression in primary school-age for boys has a greater predictive value for another medical consultation due
CRediT authorship contribution statement
Michael Frey: Conceptualization, Methodology, Writing - original draft, Writing - review & editing. Viola Obermeier: Conceptualization, Methodology, Visualization, Data curation, Formal analysis. Rüdiger von Kries: Conceptualization, Methodology, Supervision, Project administration. Gerd Schulte-Körne: Conceptualization, Methodology, Supervision, Project administration.
Declaration of competing interest
None.
Acknowledgements
The authors thank the BARMER health insurance for allowing the usage of their data warehouse for these analyses. No funding or grants were received for this manuscript.
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