Increase of internalized mental health symptoms among adolescents during the last three decades.

Background: Previous studies suggest an overall increase of adolescent mental health symptoms globally since the 1980s until today, especially an increase of internalizing symptoms in girls. Due to methodological limitations of these studies, further studies are warranted to obtain a more solid knowledgebase. Methods: This study was cross-sectional and compared two separate but geographically identical groups of adolescents in a middle-sized industrial municipality in Northern Sweden at two time-points [(i) 1981, n = 1083, (505 girls, 577 boys), response rate 99.7%; (ii) 2014, n = 682, (338 girls, 344 boys), response rate 98.3%]. All students in their last year of compulsory school were included. The same self-report questionnaire, consisting of four sub-scales (functional somatic-, anxiety-, depressive symptoms and conduct problems), was used at both occasions. Data were analyzed with descriptive statistics, two-way ANOVA and general linear model. Results: Symptoms of anxiety and depression and functional somatic symptoms, increased among both boys and girls from 1981 until 2014 (P < 0.001 for all subscales), and the increase of these symptoms was higher in girls. Conduct problems were significantly higher in boys in 1981 and decreased over time so that in 2014 there was no longer a significant difference between boys and girls regarding conduct problems (P = 0.286). Conclusion: In this population-based study spanning over 30 years, both girls and boys showed increasing internalizing problems, while conduct problems decreased. To halt this trend, we need a deeper understanding of the impact of the major societal changes that have occurred during the last three decades.