Background Adolescence represents a crucial developmental period in shaping mental health trajectories. In this study, we investigated the effect of the COVID-19 pandemic on mental health and substance use during this sensitive developmental stage. MethodsIn this longitudinal, population-based study, surveys were administered to a nationwide sample of 13-18-yearolds in Iceland in October or February in 2016 and 2018, and in October, 2020 (during the COVID-19 pandemic). The surveys assessed depressive symptoms with the Symptom Checklist-90, mental wellbeing with the Short Warwick Edinburgh Mental Wellbeing Scale, and the frequency of cigarette smoking, e-cigarette use, and alcohol intoxication. Demographic data were collected, which included language spoken at home although not ethnicity data. We used mixed effects models to study the effect of gender, age, and survey year on trends in mental health outcomes. Findings 59 701 survey responses were included; response rates ranged from 63% to 86%. An increase in depressive symptoms (β 0•57, 95% CI 0•53 to 0•60) and worsened mental wellbeing (β -0•46, 95% CI -0•49 to -0•42) were observed across all age groups during the pandemic compared with same-aged peers before COVID-19. These outcomes were significantly worse in adolescent girls compared with boys (β 4•16, 95% CI 4•05 to 4•28, and β -1•13, 95% CI -1•23 to -1•03, respectively). Cigarette smoking (OR 2•61, 95% CI 2•59 to 2•66), e-cigarette use (OR 2•61, 95% CI 2•59 to 2•64), and alcohol intoxication (OR 2•59, 95% CI 2•56 to 2•64) declined among 15-18-year-olds during COVID-19, with no similar gender differences.Interpretation Our results suggest that COVID-19 has significantly impaired adolescent mental health. However, the decrease observed in substance use during the pandemic might be an unintended benefit of isolation, and might serve as a protective factor against future substance use disorders and dependence. Population-level prevention efforts, especially for girls, are warranted.Funding Icelandic Research Fund.

Interest in the relationship between health behaviours and academic achievement has recently intensified in the face of an epidemic of childhood and adolescent obesity and converging school reforms in the United States and other nations with advanced economies. Epidemiologic research has demonstrated that poor diet and lack of adequate physical activity place children at risk for being overweight and obese and thus influence future health status. Additional research has also shown that children and adolescents whose diets are nutritious and whose participation in physical activity is high tend to perform better on various measures of cognitive performance and academic achievement. We analysed cross-sectional survey data from 5810 Icelandic school children to explore the relationship between selected health behaviours and academic achievement. Body mass index, diet and physical activity explained up to 24% (P < 0.01) of the variance in academic achievement when controlling for gender, parental education, family structure and absenteeism. Variance explained increases to 27% when depressed mood (P < 0.05) and self-esteem (P < 0.01) are added to the model, but confounds the role of physical activity. Although not robust, these findings are consistent with previous work and affirm the complexity of the relationship of health to academic achievement.

This study tested a structural equation model to estimate the relationship between health behaviors, body mass index (BMI), and self-esteem and the academic achievement of adolescents. The authors analyzed survey data from the 2000 study of Youth in Iceland , a population-based, cross-sectional sample of 6,346 adolescents in Iceland. The model demonstrated good fit with chi-square of 2685 (n = 5,810, df = 180), p < .001, Comparative Fit Index value of .94, and a root mean square error of approximation of .049. Lower BMI, physical activity, and good dietary habits were all associated with higher academic achievement; however, health behavior was positively and robustly associated with greater self-esteem. Self-esteem was positively influenced both through physical activity (beta = .16) and the consumption of fruits and vegetables (beta = .14). In contrast, poor dietary habits negatively influenced self-esteem and academic achievement, and self-esteem was negatively influenced by increasing levels of BMI (beta = -.05).

SUMMARYData from the European School Survey Project on Alcohol and other Drugs have shown that adolescent substance use is a growing problem in western and particularly Eastern European countries. This paper describes the development, implementation and results of the Icelandic Model of Adolescent Substance Use Prevention. The Icelandic Model is a theoretically grounded, evidence-based approach to community adolescent substance use prevention that has grown out of collaboration between policy makers, behavioural scientists, field-based practitioners and community residents in Iceland. The intervention focuses on reducing known risk factors for substance use, while strengthening a broad range of parental, school and community protective factors. Annual cross-sectional surveys demonstrate the impact of the intervention on substance use among the population of 14-to 16-year-old Icelandic adolescents. The annual data from two cohorts of over 7000 adolescents (.81% response rate) show that the proportions of those who reported being drunk during the last 30 days, smoking one cigarette or more per day and having tried hashish once all declined steadily from 1997 to 2007. The proportions of adolescents who reported spending time with their parents and that their parents knew with whom they were spending their time increased substantially. Other community protective factors also showed positive changes. Although these data suggest that this adolescent substance use prevention approach successfully strengthened a broad range of parental, school and community protective factors, the evidence of its impact on reducing substance use needs to be considered in light of the correlational data on which these observations are based.