PhD defence M.S. (Michel) Smit

In the thesis "Health Effects of Lifestyle Promotion among Youth," two main objectives are leading: 1.) the association between organized activities and mental health in children and adolescents, and 2.) the long-term effects of primary school-based interventions for the prevention of obesity.

The first part demonstrates favorable associations between organized sports activities and mental health in children and adolescents. There was insufficient evidence available to draw conclusions about the relationship between other types of organized activities and mental health. Organized sports activities are a promising starting point for future interventions to prevent mental health problems.

The second part investigates the long-term effects of primary school-based interventions for obesity prevention. A systematic review and meta-analysis found no convincing evidence for long-term effects on indicators of overweight and obesity. In a naturalistic effect evaluation and longitudinal cohort study no positive long-term effects of Lekker Fit! on a broad set of health outcomes were found.

The thesis emphasizes the need for continuous monitoring of intervention effects and more initiatives to improve fitness among youth in the city of Rotterdam. For effective obesity prevention, additional interventions or extension of existing programs to secondary schools might be necessary.