Highlights This umbrella review included six systematic reviews of lower quality. A small positive impact of organized sport activities on youth mental health was found. Only two systematic reviews that studied organized non-sport activities could be included. Mixed results were found for impact of organized non-sport activities on youth mental health. Mediation or confounding through physical activity needs further study.

IntroductionPreventive interventions to reduce overweight and obesity in childhood and adolescence are studied on their effectiveness worldwide. A number with positive results. However, long-term effects of these interventions and their potentially wider influence on well-being and health have been less studied. This study aims to evaluate the long-term effects of a multicomponent intervention in elementary school children targeting individual behaviour as well as environment (Lekker Fit!). The primary outcomeis body mass index and the secondary outcomes are waist circumference, weight status, physical fitness, lifestyle, psychosocial health and academic performance.Methods and analysisIn a naturalistic effect evaluation with a retrospective, controlled design adolescents in secondary schools, from intervention and non-intervention elementary schools, will be compared on a wide set of outcome variables. Data will be collected by questionnaires and through anthropometric and fitness measurements by trained physical education teachers and research assistants. Baseline data consist of measurements from the adolescents at the age of 5 years old and are gathered from preventive youth healthcare records, from before the intervention took place. Multilevel regression models will be used and adjusted for baseline measurements and potential confounding variables on the individual and environmental level. Furthermore, propensity scores will be applied.Ethics and disseminationThe study has been approved by the Medical Research Ethics Committee of the Erasmus Medical Centre, Rotterdam, The Netherlands (permission ID: MEC-2020-0644). Study findings will be disseminated in peer-reviewed journals and by conference presentations.Trial registration numberNL8799. Pre-results.

Introduction: This systematic review and meta-analysis investigate the long-term effects of primary school-based obesity prevention interventions on body-mass index (and z-scores), waist circumference (and z-scores) and weight status.Methods: Four databases were searched for studies from date of inception until June 8th, 2021. We included randomized controlled trials (RCT) and non-RCTs investigating effects ≥12 months post-intervention of primary school-based interventions with intervention duration ≥6 months and containing a diet and/or physical activity component on outcomes of interest. Articles were assessed on risk of bias and methodological quality by RoB2 and ROBINS-I. Meta-analysis was performed and results were narratively summarized. Evidence quality was assessed with GRADE.Results: Nineteen studies were included, 9 were pooled in a meta-analysis. No longterm effects were found on body-mass index (+0.06 kg/m 2 ; CI95% = À0.38, 0.50; I 2 = 66%), body-mass index z-scores (À0.08; CI95% = À0.20, 0.04; I 2 = 36%), and waist circumference (+0.57 cm; CI95% = À0.62, 1.75; I 2 = 13%). Non-pooled studies reported mixed findings regarding long-term effects on body-mass index, bodymass index z-scores and weight status, and no effects on waist circumference and waist circumference z-scores. Evidence certainty was moderate to very low. Discussion: No clear evidence regarding long-term effects of primary school-based interventions on obesity-related outcomes was found. Recommendations for further research and policy are discussed. Prospero registration ID: CRD42021240446.

Previous studies conducted mainly among adolescents have found associations between participation in sport organised leisure-time activities (OLTAs) and mental health problems (MHP). Fewer research studies have been performed to primary school-aged children and to organised non-sport OLTAs. Therefore, the objective is to examine whether there is an association between participation in sport and non-sport OLTAs and a high risk of MHP in 4- to 12-year-olds. Data were used on 5010 children from a cross-sectional population-based survey conducted between May and July 2018 in Rotterdam, the Netherlands. Associations between sport OLTAs, non-sport OLTAs and breadth of OLTAs and a high risk of MHP were explored using logistic regression models adjusting for sociodemographic characteristics, stressful life events and physical activity. Of all children, 58% participated in sport OLTAs and 22% in non-sport OLTAs. The proportion of children with high risk of MHP among participants in sport OLTAs is smaller than among non-participants (OR 0.66, 95% CI: 0.53, 0.81). The proportion of children with high risk of MHP among participants in non-sport OLTAs is smaller than among non-participants (OR 0.69, 95% CI: 0.53, 0.91). The proportion of children with a high risk of MHP among participants in 1 category of OLTAs (OR 0.61, 95% CI: 0.49, 0.76) and in 2–5 categories of OLTAs (OR 0.48, 95% CI: 0.32, 0.71) is smaller than among non-participants.  Conclusion: The proportion of children with high risk of MHP among participants in OLTAs is smaller than among non-participants. What is Known:• Around 10–-20% of children and adolescents experiences mental health problems.• Sport organised leisure-time activities have been found to be associated with a lower risk of mental health problems in adolescents. What is New:• The proportion of children with a high risk of mental health problems in participants in organised leisure-time activities is smaller than among non-participants.• The proportion of children with a high risk of mental health problems in participants with a higher breadth of organised leisure-time activities is smaller compared to non-participants.