This chapter provides a synthesis of three earlier published studies (Garmy et al. 2012^a; Garmy et al. 2012^b; Garmy et al. 2013) (survey I) as well as previously unpublished results from a survey conducted in 2013 among students aged 16 (survey II).

Objective: The aim was to investigate the effects of sleep, television use and texting and computer habits on overweight, enjoyment of school and feelings of tiredness at school in school-age children and adolescents.

Methods: This cross-sectional study was conducted in Sweden on schoolchildren aged 6, 7, 10, 14 and 16. A questionnaire which had been satisfactorily tested for validity and reliability was distributed to the children (n=3011 in survey I; n=204 in survey II).

Results: Children who slept less than the median length of time reported enjoying school to a lesser degree. Fewer hours of sleep were found to be associated with having a bedroom television, using the television or computer more than 2 hours a day, being tired at school, and having difficulties in sleeping and waking up. Overweight and obesity were found in 15.8% of the study population; obesity alone was found in 3.1%. Relationships between lifestyle factors and overweight were studied using multivariate logistic regression analysis. Having a bedroom television and using the television more than 2 hours per day were found to be associated with overweight, but using the computer more than 2 hours a day was not. About 61% of the students aged 16 reported checking Facebook or social media at least once a day, and 27% reported doing so more than 10 times a day. One fourth of the students aged 16 had a habit of sending or receiving text messages at night at least once a week. Texting at night and frequent checking of Facebook and social media sites were related to sleep problems.

Conclusions: Educating schoolchildren and their parents regarding matters of optimal sleep and how media habits affect sleep, overweight and learning is considered an important task.