Background: Mental health problems are a worldwide public health burden. The literature concerning the mental health benefits from physical activity among adults has grown. Adolescents are less studied, and especially longitudinal studies are lacking. This paper investigates the associations between weekly hours of physical activity at age 15-16 and mental health three years later.

BackgroundSchool drop-out is a problem all over the world with adverse life-course consequences. The aim of this paper is to study how internalising and externalising problems in the 10th grade are associated with non-completion of upper secondary school, and to examine the mediating role of grade points in the 10th grade across general academic and vocational tracks in upper secondary school. We also study the impact of health behaviour.MethodsPopulation-based health surveys were linked with Norwegian registries on education and sociodemographic factors (n = 10 931). Mental health was assessed by the self-report Strengths and Difficulties Questionnaire. Logistic regression was used to analyse the relations between mental health and health behaviour in 10th grade and non-completion of upper secondary school. The mediating effect of grade points was studied by causal mediation analysis.ResultsAdolescents not completing upper secondary school reported more externalising problems and girls more internalising problems in the 10th grade, after adjustments. Smoking and physical inactivity increased the odds of non-completion of upper secondary school. Causal mediation analyses showed that a reduction in externalising problems of 10 percentage points led to lower rates of non-completion of 4–5 percentage points, and about three-quarters of this total effect was mediated by grades. For internalising problems the total effect was significant only for girls (1 percentage point), and the mediated effect of grades was about 30%. The effect of mental health problems on school dropout was mainly the same in both vocational and general tracks.ConclusionsAssuming a causal relationship from mental health problems to school performance, this study suggests that externalising problems impair educational attainment. A reduction of such problems may improve school performance, reduce school drop-out and reduce the adverse life-course consequences.

To some extent the theoretically proposed five-factor structure of the Norwegian version of the SDQ self-report was supported in 15- to 16-year-old adolescents. However, the results of more detailed analyses raise questions about the interpretation of some subscales. When applying this screening method to Norwegian adolescents, our results suggest that the use of the total difficulty score of the SDQ in screening youth should be preferred over the subscale scores.

Background: More research on factors associated with physical activity and the decline in participation during adolescence is needed. In this paper, we investigate the levels, change, and stability of physical activity during the late teens among ethnic Norwegians and ethnic minorities, and we examine the associations between physical activity and socio-demographic factors.

BackgroundSelection bias is a threat to the internal validity of epidemiological studies. In light of a growing number of studies which aim to provide DNA, as well as a considerable number of invitees who declined to participate, we discuss response rates, predictors of lost to follow-up and failure to provide DNA, and the presence of possible selection bias, based on five samples of adolescents.MethodsWe included nearly 7,000 adolescents from two longitudinal studies of 18/19 year olds with two corresponding cross-sectional baseline studies at age 15/16 (10th graders), and one cross-sectional study of 13th graders (18/19 years old). DNA was sampled from the cheek mucosa of 18/19 year olds. Predictors of lost to follow-up and failure to provide DNA were studied by Poisson regression. Selection bias in the follow-up at age 18/19 was estimated through investigation of prevalence ratios (PRs) between selected exposures (physical activity, smoking) and outcome variables (general health, mental distress, externalizing problems) measured at baseline.ResultsOut of 5,750 who participated at age 15/16, we lost 42% at follow-up at age 18/19. The percentage of participants who gave their consent to DNA provision was as high as the percentage that consented to a linkage of data with other health registers and surveys, approximately 90%. Significant predictors of lost to follow-up and failure to provide DNA samples in the present genetic epidemiological study were: male gender; non-western ethnicity; postal survey compared with school-based; low educational plans; low education and income of father; low perceived family economy; unmarried parents; poor self-reported health; externalized symptoms and smoking, with some differences in subgroups of ethnicity and gender. The association measures (PRs) were quite similar among participants and all invitees, with some minor discrepancies in subgroups of non-western boys and girls.ConclusionsLost to follow-up had marginal impact on the estimated prevalence ratios. It is not likely that the invitation to provide DNA influenced the response rates of 18/19 year olds. Non-western ethnicity, male gender and characteristics related to a low social class and general and mental health problems measured at baseline are associated with lost to follow-up and failure to provide DNA.