title: School-based physical activity and changes in adiposity.
abstract: OBJECTIVE
  School-based physical education (PE) is often proposed as a strategy for obesity prevention, but many trials have found non-significant effects on body mass index (BMI). We examined the impact of school PE on adiposity in adolescents, using an ecological analysis to relate the number of PE sessions to changes in BMI and waist circumference.
  
  
  METHODS
  Five-year, longitudinal, school-based study involving 34 secondary schools in London, England. Students were aged 11-12 years at baseline. Twenty-five schools reported one weekly session of PE, seven schools reported two sessions and two boys' schools reported three sessions. Weights, heights and waist circumferences were measured annually, and complete data from the first and fifth years of the study were available on 2727 students. Analyses compared anthropometric changes between students in schools with higher or lower amounts of PE time. In boys, the comparisons were between those receiving 1, 2 or 3 weekly sessions. In girls, comparisons were between those receiving one and two sessions.
  
  
  RESULTS
  There were no differences in BMI changes or the percentage of students classified as obese between schools of higher and lower frequency of PE. However, using unadjusted data, there were lower gains in waist circumference in boys and girls from the higher PE schools. Controlling for baseline demographic and anthropometric characteristics, boys in schools providing 3 weekly PE sessions gained on average approximately 3 cm less than boys in schools providing one or two sessions (P<0.001). Differences in girls were in the same direction but not significant.
  
  
  CONCLUSIONS
  Higher levels of school PE were associated with lower gains in adiposity in boys. This strengthens the case for including recommendations on school PE time as part of population strategies to control adolescent obesity.
authors.affiliation: Cancer Research UK Health Behaviour Unit, Department of Epidemiology and Public Health, University College London, London, UK. j.wardle@ucl
authors.forename: J
authors.initials: J
authors.lastname: Wardle
authors.forename: N H
authors.initials: NH
authors.lastname: Brodersen
authors.forename: D
authors.initials: D
authors.lastname: Boniface
mesh_terms: D000273:Adipose Tissue / Q000473:pathology*; D050154:Adiposity / Q000208:ethnology / Q000502:physiology*; D000293:Adolescent; D002648:Child; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D009765:Obesity / Q000473:pathology* / Q000503:physiopathology; D050177:Overweight / Q000473:pathology / Q000503:physiopathology; D010806:Physical Education and Training; D015995:Prevalence; D012737:Sex Factors; D012959:Socioeconomic Factors; D013334:Students; D049629:Waist-Hip Ratio