Impact of school outdoor environment upon pupils' physical activity and sun exposure across ages and seasons

Abstract

Background and aims: Among children, the lack of physical activity (PA) is widespread in developed countries. Further, the majority of all skin cancers depend on an overexposure to solar ultraviolet radiation (UVR) in early life. The combination of sufficient PA and suberythemal UVR exposure (potentially sufficient for vitamin D production) dispersed over the day is vital to general wellbeing and bone health, especially in growing children and adolescents. However, long regulated school days entail less free mobility and outdoor stay, which may jeopardize the opportunities for cohesive intense physical activity (PA) and suberythemal UVR exposure. The impact of the school outdoor environment upon schoolchildren’s PA has been studied but not in combination with the exposure to UVR from the sun during the school day in children of different ages during one academic year containing different seasons. The overall aim for this thesis was to examine the cross-sectional impact of outdoor environments at compulsory school level in different seasons upon PA and solar UVR exposure in Swedish pupils.

Material and Methods: The impact of school outdoor environment upon pupils' physical activity and UVR exposure during free-mobility, scheduled time and physical education (PE) were studied in 196 pupils aged 7-15 years (grades 2, 5, and 8) at four schools in mid-southern Sweden during 5 consecutive days each in September, March and May. Actigraph GT3X+ Activity monitors were used for PA assessments and for separation of indoor from outdoor stay, supplementary to ocular observation. Predictors for PA during school stay, expressed as mean daily accelerometer counts and time in different PA intensities were measured per season, day, grade and gender. For individual assessment of erythemally effective UVR (joule per exposed m2 of the skin), a polysulphone film dosimeter badge was pinned to the top of the pupils’ right shoulders and worn during school-time during the entire week. Their individual UVR exposures were related to and expressed as fractions of total available ambient UVR in the schools’ outdoor environments which differed considering amount of shade, vegetation, and peripheral city-scape quantified as percentage of free sky view calculated by fish-eye photography. Questionnaires and diaries were applied to control for confounders.

Results: Overall, free-living PA outdoors generated the highest mean accelerometer counts for moderate and vigorous physical activity (MVPA), and together with outdoor physical education contributed with 50% of total mean accelerometer counts though representing only 25% of the total school time. Season, age, gender and weather had an impact on both PA and UVR exposure, with less PA and UVR exposure. In March, in inclement weather both PA and UVR exposure dropped, especially among older pupils and girls. During all seasons both MVPA counts and UVR exposures were significantly higher among 2nd graders vs. 5th and 8th graders. In September and March play at sport fields had a positive impact on pupils’ PA and suberythemal sun exposure (potentially sufficient for vitamin D production). Among 2nd and 5th graders and in September this interaction between attributes of the physical environment and level of PA and UVR exposure was pronounced. In May overexposure to UVR did occur, though green settings with trees and shrubs and fixed play equipment close to the greenery protected from hazardous UV exposure and promoted high levels of MVPA.

Conclusions: More time outdoors, at all seasons, would favorably increase school children's chances of reaching recommended levels of PA. There is a potential for prolonged suberythemal outdoor stay for play in open areas during fall and early spring at Lat.56oN. Outdoor activities in such settings should therefore be encouraged. In late spring, long outdoor exposures of the youngest pupils warrant UVR-protective outdoor environment. Access to vegetation and/or shaded structures (e.g. trees, bushes, roofs) attractive for play should be provided for.