title: Low sleep and low socioeconomic status predict high body mass index: a 4-year longitudinal study of Australian schoolchildren.
abstract: OBJECTIVE
  The objective of this study was to examine the longitudinal relationships between body mass index (BMI), sleep duration and socioeconomic status (SES) in a 4-year cohort of 939 children aged 7-12 years.
  
  
  METHODS
  Children and their mothers completed an annual questionnaire to assess usual weekday sleep and wake times, amount of sleep, physical activity, parental education and school SES. 93% of children were enrolled (939/1010) and retention was 88%, 83% and 81% in consecutive years. Height and weight were measured annually.
  
  
  RESULTS
  BMI increased with decreasing amount of sleep and less sleep predicted greater International Obesity Task Force measures of obesity and overweight. In all 4 years, after controlling for baseline BMI, low SES was a significant predictor of high BMI. Children in the upper tertile of sleep in year 1 had a 2.3 kg lower weight gain (standard error [SE]: 0.5) between years 1 and 4 (P < 0.0001) than children in the lower tertile of sleep and a 0.45 kg m(-2) lower increase in BMI (SE: 0.15) (P = 0.004). The difference between children with consistently low and high sleep duration over 4 years was 1 BMI point. Those with the lowest BMI were the children with both high SES and high sleep duration. PA was not associated with BMI.
  
  
  CONCLUSIONS
  Both low SES and short sleep duration predict obesity risk in children after controlling for baseline BMI and this trend becomes stronger as children enter adolescence. Obesity prevention should include a sleep promotion component and this may be more beneficial to children of low SES and/or socially disadvantaged backgrounds.
authors.affiliation: Faculty of Education & Social Work, University of Sydney, Sydney, NSW, Australia. jennifer.odea@sydney.edu.au
authors.forename: J A
authors.initials: JA
authors.lastname: O'Dea
authors.forename: M J
authors.initials: MJ
authors.lastname: Dibley
authors.forename: N M
authors.initials: NM
authors.lastname: Rankin
mesh_terms: D000293:Adolescent; D000367:Age Factors; D000704:Analysis of Variance; D015992:Body Mass Index; D016009:Chi-Square Distribution; D002648:Child; D005260:Female; D006801:Humans; D016014:Linear Models; D008137:Longitudinal Studies; D008297:Male; D009043:Motor Activity; D009517:New South Wales / Q000453:epidemiology; D009765:Obesity / Q000453:epidemiology* / Q000503:physiopathology; D050177:Overweight / Q000453:epidemiology* / Q000503:physiopathology; D018570:Risk Assessment; D012307:Risk Factors; D012890:Sleep; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires; D013997:Time Factors