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Attained body mass index among children attending outdoor or conventional kindergartens

BACKGROUND: Studies have shown that outdoor activities are inversely associated with adiposity, but little is known about outdoor kindergartens as a potential intervention for healthy weight development. METHODS: We included 1544 children from outdoor kindergartens and 1640 from conventional kindergartens. Anthropometry was measured by school health nurses when the children were 6 to 8 years old. The first available measure of attained body mass index z-score (BMIz) after school entrance was included as the primary outcome, while risk of attaining overweight (including obesity) was included as a secondary outcome. Register-based information was available on potential confounding factors. Regression models were constructed to examine differences in study outcomes between children attending outdoor and conventional kindergartens. RESULTS: Our basic models, with information on outcome, kindergarten type and birth weight, showed a borderline statistically significantly lower attained BMIz (-0.07 [95% CI: -0.14, 0.00], P=0.060) and a lower risk of overweight (adjusted risk ratio: 0.83 [95% CI: 0.72, 0.97], P=0.016) among children attending outdoor kindergartens compared to conventional kindergartens. When additionally adjusting for sociodemographic factors, there was no evidence of differences in attained BMIz (P=0.153) or overweight (P=0.967). CONCLUSION: Our results do not support outdoor kindergartens as an intervention for healthy weight development.