Rannsókn við Háskóla Íslands


An extensive long-term reserach of the health status of Icelandic youth and their relation to sleep, physical activity and school environment. The study is conducted by scientists at the University of Iceland.

The overall aim of this research project was to investigate the physical health status, in particular longitudinal changes in body composition, physical activity, sleep, mental aspects and fitness in a cohort of Icelandic children (born in 1999),
from age 7 and 9 years old to 15 and 17 years old.

Furthermore, to assess how these factors are associated with objective measures of sleeping patterns and physical activity in adolescence and the longitudinal change from age 15 to 17.


Results at age 15 revealed that almost half of the participants fulfilled the physical activity recommendations according to the questionnaire but weekly averages were not different between sexes. Girls and boys did not differ in subjective nor objective measures of sleep.

Adolescence have a late bedtime and average sleep duration on school days was only 6.2 hours per night and 7.3 hours on non-school days. Higher variance (SD) in sleep was associated with higher body fat percentage.

Less screen time and more frequent vigorous physical activity were each associated with reporting fewer symptoms of depression, anxiety, low self-esteem, and life dissatisfaction. There were associations between higher screen usage and variance in sleeping patterns.

The total activity decreased 13.1% from age 15 to 17 and that change was only observable on school days, but not on non-school days.

Participation in sports decreased 25% between age 15 and 17. Boys and girls were taller, heavier and had higher BMI at age 17 than at age 15. Body fat percentage did not change significantly for either sex.

Over the two year span time in bed decreased from 7.5 h/night at age 15 to 7.1 h/night at age 17 and sleep duration decreased from 6.6 h/night to 6.2 h/night from age 15 to 17. Increased variability was higher for those who reported higher screen time, especially among boys.

Students attending secondary schools with college style schedules slept longer than students in schools with traditional style schedules did. No difference was found in change in activity between the two school systems.



Adolescence marks a period of widespread changes in a persons’ life, due to the substantial physical- and mental development-taking place at that age.

Furthermore, increased autonomy and the altered educational and social environment transpiring from primary to secondary school plays a big role in the adolescents life.

Knowledge on the development of various lifestyle factors during adolescence, and its association with daily competency, will yield valuable information for health and educational authorities in Iceland.


The Health Behaviour of Icelandic Youth research is organized by investigators at the School of Education, University of Iceland, in collaboration with the city of Reykjavík, Directorate of health, Icelandic heart association and the National Institute of Health in USA.

For information please contact: heilsuhegdun@hi.is

Principal investigator of the study:
Erlingur Johannsson, professor: erljo@hi.is