BMJ  2007;335:194 (28 July), doi:10.1136/bmj.39238.399444.55 (published 25 June 2007)

Research

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

Tim J Cole, professor of medical statistics1, Katherine M Flegal, senior research scientist2, Dasha Nicholls, consultant child and adolescent psychiatrist3, Alan A Jackson, professor of human nutrition4

1 Centre for Paediatric Epidemiology and Biostatistics, UCL Institute of Child Health, London WC1N 1EH, 2 National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville MD 20782, USA, 3 Department of Child and Adolescent Mental Health, Great Ormond Street Hospital for Children, London, 4 Institute of Human Nutrition, University of Southampton, Southampton

Correspondence to: T J Cole tim.cole{at}ich.ucl.ac.uk

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.


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Rapid Responses:

Read all Rapid Responses

Thinness,BMI and Body Size
C Kevin Connolly
bmj.com, 1 Aug 2007 [Full text]
New criteria for thinness are very close to Dutch criteria for (severe) underweight
Stef van Buuren
bmj.com, 6 Aug 2007 [Full text]
Re: Thinness,BMI and Body Size
Tim J Cole
bmj.com, 6 Oct 2007 [Full text]
Clarifying the grades
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