title: Seasonal reduction in physical activity and flow-mediated dilation in children.
abstract: OBJECTIVE
  cardiovascular disease is a process that has its origins in childhood. Endothelial dysfunction is the earliest detectable manifestation of cardiovascular disease. This study aimed to assess the impact of seasonal changes in physical activity (PA) and body composition on conduit artery endothelial function in children.
  
  
  METHODS
  we studied 116 children (70 girls aged 10.7 ± 0.3 yr and 46 boys aged 10.7 ± 0.3 yr) on two occasions; in the northern summer (June) and late autumn (November). We assessed flow-mediated dilation (FMD) using high-resolution Doppler ultrasound. Body composition was measured by dual-energy x-ray absorptiometry. PA was assessed using accelerometry.
  
  
  RESULTS
  FMD (10.0% ± 4.3% to 7.9% ± 3.9%, P < 0.001) and PA (94.1 ± 34.8 to 77.8 ± 33.7 min·d, P < 0.01) decreased, while percentage body fat increased (27.6% ± 6.8% to 28.0% ± 6.6%, P < 0.001) between summer and autumn. Decreases in FMD correlated with decreases in high-intensity PA (r = 0.23, P = 0.04), and change in high-intensity PA was the only predictor of change in FMD. No relationships were evident between changes in body composition and FMD.
  
  
  CONCLUSIONS
  vascular function decreased between summer and autumn in this cohort. There were no relationships between change in FMD and changes in body composition or low/moderate-intensity PA. The associations between FMD and high-intensity PA suggests that future interventions should encourage this form of behavior, particularly at the times of year associated with lower PA.
authors.affiliation: Research Institute for Sport and Exercise Science, Liverpool John Moore's University, Liverpool, UNITED KINGDOM.
authors.forename: Nicola Dominique
authors.initials: ND
authors.lastname: Hopkins
authors.forename: Gareth
authors.initials: G
authors.lastname: Stratton
authors.forename: Toni M
authors.initials: TM
authors.lastname: Tinken
authors.forename: Nicola D
authors.initials: ND
authors.lastname: Ridgers
authors.forename: Lee E
authors.initials: LE
authors.lastname: Graves
authors.forename: Nicola
authors.initials: N
authors.lastname: McWhannell
authors.forename: N Tim
authors.initials: NT
authors.lastname: Cable
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Green
mesh_terms: D015502:Absorptiometry, Photon; D001823:Body Composition; D001916:Brachial Artery / Q000000981:diagnostic imaging / Q000502:physiology; D002648:Child; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D012621:Seasons; D014463:Ultrasonography; D014664:Vasodilation / Q000502:physiology*