Do the school's outdoor environments impact children's health behavior? Students are confined to and exposed to outdoor environment which happens to be at their disposal during compulsory school time. The cross-cutting health-promoting potential of outdoor environment, and the use of it, is therefore important. We have studied the combined impact of school outdoor environment in terms of playground features, space, surface, terrain and vegetation upon physical activity (PA) and sun exposure across ages and seasons. From an early age physical activity promotes physical capacity, quality of life and self-esteem, as well as it reduces the risk of common diseases. There is evidence that outdoor stay is a strong predictor of physical activity at preschool and primary school outdoor play time. One backlash of outdoor stay may be hazardous exposure to ultraviolet radiation (UVR). Sunburn at an early age increases the risk of skin cancer in late spring and summer. Too little sun exposure for the body production of vitamin D during the rest of the year could also be a health problem for children especially at higher latitudes.

A quasi-experimental, longitudinal cohort study design was used. Four schools in the Middle and Southern part of Sweden, with outdoor environments differing in playground features, vegetation, topography and space, were analyzed during one school year in September, March and May 2012-13. A sample of 196 children was drawn from the eligible children in the grades 2, 5 and 8, aged 7-14 years. The students’ PA was monitored with Actigraph accelerometers GT3X+, showing the time spent at different intensity levels during the use of the school playground during outdoor time. UV radiation was monitored with UVR sensible polysulphone badges (PS-dosimeters) attached to each child’s shoulder during school outdoor time. Maps were used to mark places where the children stayed and what they did during outdoor time.

The mean amount of PA spent at a moderate to vigorous intensity level (MVPA) was 47% of outdoor time compared with 13% of indoor time. The amount of MVPA during outdoor stay (mean=39 minutes) was high throughout all seasons in three of the four schools. Mean MVPA during outdoor stay declined with increasing age, and boys accumulated more MVPA than girls at all ages (p <0.001). The amount of used outdoor play area was positively correlated to MVPA (p<0.001). Large planned ball areas correlated with increased physical activity levels in 5th graders in September and May (p<0.001) . Ball play (football, floor ball and basketball) dominate in high active areas. Second graders were exposed to more UV radiation than 5th and 8th graders but did not exceed the recommended threshold level of 200 joule/m2. Exposure to UVR increased with increasing MVPA during outdoor stay, (p<0.001). Green areas with shrubs and trees were popular playgrounds and stimulated creativity play and protected against excessive UVR in May but did not increase MVPA during the year.

Outdoor environment and outdoor play time have a high impact on both physical activity and UV radiation and are important health promoting factors during school time.