title: Contrasting longitudinal and cross-sectional relationships between insulin resistance and percentage of body fat, fitness, and physical activity in children-the LOOK study.
abstract: BACKGROUND
  Knowledge of individual changes in insulin resistance (IR) and longitudinal relationships of IR with lifestyle-associated factors are of important practical significance, but little longitudinal data exist in asymptomatic children. We aimed to determine (a) changes in the homeostatic model of insulin resistance (HOMA-IR) over a 2-yr period and (b) comparisons of longitudinal and cross-sectional relationships between HOMA-IR and lifestyle-related risk factors.
  
  
  METHODS
  Our subjects, 241 boys and 257 girls, were assessed at age 8.1 yr (SD 0.35) and again 2 yr later for fasting blood glucose and insulin, dual X-ray absorptiometry-assessed percentage of body fat (%BF), pedometer-assessed physical activity (PA), and cardio-respiratory fitness (CRF) by multistage running test.
  
  
  RESULTS
  HOMA-IR was initially 9% greater in girls than boys and 27% greater 2 yr later. There was no evidence of longitudinal relationships between HOMA-IR and %BF in boys or girls, despite significant cross-sectional relationships (p < 0.001). In boys, there was evidence of a longitudinal relationship between HOMA-IR and both PA (p < 0.001) and CRF (p = 0.05). In girls, we found a cross-sectional relationship between HOMA-IR and CRF (p < 0.001).
  
  
  CONCLUSIONS
  HOMA-IR increases between 8 and 10 yr of age and to a greater extent in girls. Longitudinal, unlike cross-sectional, relationships do not support the premise that body fat has any impact on HOMA-IR during this period or that PA or CRF changes affect HOMA-IR in girls. These data draw attention to difficulties in interpreting observational studies in young children.
authors.affiliation: Medical School, Australian National University and Commonwealth Institute, Canberra, ACT, Australia. rtelford@cominst.org.au
authors.forename: Richard D
authors.initials: RD
authors.lastname: Telford
authors.forename: Ross B
authors.initials: RB
authors.lastname: Cunningham
authors.forename: Jonathan E
authors.initials: JE
authors.lastname: Shaw
authors.forename: David W
authors.initials: DW
authors.lastname: Dunstan
authors.forename: Antony R A
authors.initials: AR
authors.lastname: Lafferty
authors.forename: Graham J
authors.initials: GJ
authors.lastname: Reynolds
authors.forename: Peter E
authors.initials: PE
authors.lastname: Hickman
authors.forename: Emma
authors.initials: E
authors.lastname: Southcott
authors.forename: Julia M
authors.initials: JM
authors.lastname: Potter
authors.forename: Paul
authors.initials: P
authors.lastname: Waring
authors.forename: Rohan M
authors.initials: RM
authors.lastname: Telford
mesh_terms: D000273:Adipose Tissue; D044362:Australasia / Q000453:epidemiology; D002648:Child; D003430:Cross-Sectional Studies; D003924:Diabetes Mellitus, Type 2 / Q000453:epidemiology*; D005260:Female; D006706:Homeostasis; D006801:Humans; D007333:Insulin Resistance; D008019:Life Style; D008137:Longitudinal Studies; D008297:Male; D024821:Metabolic Syndrome / Q000453:epidemiology*; D009043:Motor Activity; D009765:Obesity / Q000453:epidemiology; D010809:Physical Fitness; D012307:Risk Factors