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Body mass index cut offs to define thinness in children and adolescents: international survey

BMJ 2007; 335 doi: (Published 26 July 2007) Cite this as: BMJ 2007;335:194
  1. Tim J Cole, professor of medical statistics1,
  2. Katherine M Flegal, senior research scientist2,
  3. Dasha Nicholls, consultant child and adolescent psychiatrist3,
  4. Alan A Jackson, professor of human nutrition4
  1. 1Centre for Paediatric Epidemiology and Biostatistics, UCL Institute of Child Health, London WC1N 1EH
  2. 2National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville MD 20782, USA
  3. 3Department of Child and Adolescent Mental Health, Great Ormond Street Hospital for Children, London
  4. 4Institute of Human Nutrition, University of Southampton, Southampton
  1. Correspondence to: T J Cole tim.cole{at}
  • Accepted 18 May 2007


Objective To determine cut offs to define thinness in children and adolescents, based on body mass index at age 18 years.

Design International survey of six large nationally representative cross sectional studies on growth.

Setting Brazil, Great Britain, Hong Kong, the Netherlands, Singapore, and the United States.

Subjects 97 876 males and 94 851 females from birth to 25 years.

Main outcome measure Body mass index (BMI, weight/height2).

Results The World Health Organization defines grade 2 thinness in adults as BMI <17. This same cut off, applied to the six datasets at age 18 years, gave mean BMI close to a z score of −2 and 80% of the median. Thus it matches existing criteria for wasting in children based on weight for height. For each dataset, centile curves were drawn to pass through the cut off of BMI 17 at 18 years. The resulting curves were averaged to provide age and sex specific cut-off points from 2-18 years. Similar cut offs were derived based on BMI 16 and 18.5 at 18 years, together providing definitions of thinness grades 1, 2, and 3 in children and adolescents consistent with the WHO adult definitions.

Conclusions The proposed cut-off points should help to provide internationally comparable prevalence rates of thinness in children and adolescents.


  • We thank Carlos Monteiro (Brazil), Sophie Leung (Hong Kong), Machteld Roede (Netherlands), and Uma Rajan (Singapore) for allowing us access to their data.

  • Contributors: TJC and DN had the original idea. TJC did most of the statistical analyses, wrote the first draft, and is guarantor. KMF did further analyses of the US data. DN provided expertise on eating disorders and AAJ provided expertise on malnutrition. All authors participated in the discussion and interpretation of the results and contributed to the final paper.

  • Funding: Research at the UCL Institute of Child Health and Great Ormond Street Hospital for Children NHS Trust benefits from funding from the NHS Executive. TJC is supported by a Medical Research Council programme grant.

  • Competing interests: None declared.

  • Ethical approval: Not required.

  • Accepted 18 May 2007
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