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CLINICAL REVIEW: Ruth R Kipping, Russell Jago, and Debbie A Lawlor Obesity in children. Part 1: Epidemiology, measurement, risk factors, and screening BMJ 2008; 337: a1824 [Full text]

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Why, oh why?

Brid Hehir   (22 October 2008)

Classifying children as overweight and obese

Adriano Cattaneo, Lorenzo Monasta   (27 November 2008)

Why, oh why? 22 October 2008
Brid Hehir, Nurse W3 6JS Send response to journal: Re: Why, oh why?	So..... why is the DH getting school nurses to weigh and measure Reception Year and Year 6 children in schools for a condition they don't allude to in their publicity, but we all understand as 'obesity', whatever that is? Competing interests: None declared
Classifying children as overweight and obese 27 November 2008
Adriano Cattaneo, Epidemiologist Institute for Maternal and Child Health Burlo Garofolo, Via dell’Istria 65/1, 34137 Trieste, Italy, Lorenzo Monasta Send response to journal: Re: Classifying children as overweight and obese	In their article, Kipping and colleagues state that "in children the effects of age, sex, and pubertal status make simple classification (of overweight and obesity) difficult".1 They cite two of the most frequently used references based on BMI: the International Obesity Task Force (IOTF) cut-offs for children 2 to 18 years of age,2 and the 2006 WHO child growth standards.3 In our opinion, both need some sort of fix. When the IOTF and another reference are applied to the same population, the former overestimates the prevalence of overweight and obesity in girls. This problem, first identified by Chinn and Rona using IOTF and UK references, seems related to the fact that the IOTF cut-offs in children are a projection of overweight (BMI¡Ý25) and obesity (BMI¡Ý30) at 18 years, and to a sex bias at 18 years in the IOTF references, because the BMI plateaus earlier in girls than boys, so that it rises in boys more than in girls from 18 to 20 years of age.4 For the WHO standards, cut-offs have not been defined yet. The use of 1, 2 and 3 z-scores as cut-offs,5 corresponding to the 84.13th, 97.72th and 99.87th centiles, respectively, generates either too wide or too narrow intervals, while the alternative use of other centiles as cut-offs (e.g. the 90th and 97th centiles) has not been proposed yet. As part of a review of existing data on the prevalence of overweight and obesity in infants and preschool children in Europe, within the activities of the HOPE (Health promotion through Obesity Prevention across Europe) project (http://www.hopeproject.eu/), we performed a simple exercise to find out how much the prevalence rates obtained with the IOTF cut-offs between 2 and 5 years of age correspond to those derived from the WHO standards. Our aim was to sort out the sex unbalance of the IOTF references and to identify possible cut-offs for the WHO standards. We used the IOTF cut-off table2 and we calculated the corresponding z-scores and centile values for the WHO standards. The Table shows how the IOTF cut -offs overestimate overweight and obesity in older ages and in girls. The IOTF and the WHO references were developed using different methods and approaches. If the IOTF approach is right, and if the WHO standards are based on better data, choosing z-scores or centiles within the ranges presented in the Table for the latter (e.g. the 90th and the 99th centiles for overweight and obesity, respectively) would allow to get results, in children 2 to 5 years of age, comparable to those obtained using the IOTF cut-offs. 1. Kipping RR, Jago R, Lawlor DA. Obesity in children. Part 1: Epidemiology, measurement, risk factors, and screening. BMJ 2008;337:a1824 2. Cole TJ, Bellizzi MC, Flegal KM, Dietz WH. Establishing a standard definition for child overweight and obesity worldwide: international survey. BMJ 2000;320:1240-3 3. WHO Multicentre Growth Reference Study Group. WHO Child Growth Standards based on length/height, weight and age. Acta Paediatr Suppl 2006;450:76-85 4. Chinn S, Rona RJ. International definitions of overweight and obesity for children: a lasting solution? Ann Hum Biol 2002;29:306-13 5. WHO. Child growth standards: training course on child growth assessment. WHO, Geneva, 2006 Table. Z-scores and centiles for the WHO standards based on IOTF cut-offs for overweight and obesity in children 2 to 5 years of age. Overweight Obesity Age in years Males Females Males Females z-scores (centile) z-scores (centile) z-scores (centile) z-scores (centile) 2.0 1.71 (95.63) 1.58 (94.29) 2.71 (99.66) 2.59 (99.52) 2.5 1.68 (95.35) 1.51 (93.45) 2.72 (99.67) 2.54 (99.45) 3.0 1.69 (95.45) 1.48 (93.06) 2.76 (99.71) 2.52 (99.41) 3.5 1.64 (94.95) 1.40 (91.92) 2.73 (99.68) 2.43 (99.25) 4.0 1.60 (94.52) 1.31 (90.49) 2.67 (99.62) 2.32 (98.98) 4.5 1.55 (93.94) 1.22 (88.88) 2.62 (99.56) 2.24 (98.75) 5.0 1.50 (93.32) 1.14 (87.29) 2.54 (99.45) 2.18 (98.54) Competing interests: None declared