Definition of childhood overweight/obesity
There is widespread agreement that for adults a body mass index (BMI)
of 25 kg/m2 constitutes overweight and 30 kg/m2 obesity, but there are no
agreed definitions for children. Cole et al  propose using BMI centile
curves and the LMS method to derive childhood standards. First, the z-
scores at age 18 years corresponding to 25 kg/m2 and 30 kg/m2 were
calculated. Next, the BMI values corresponding to these z-scores were
found for children aged 2 to 18 years. The authors thus assume that the
incidence of overweight/obesity remains constant throughout childhood.
The prevalence of overweight increases with age and, using the 1990
British reference data  and a definition of 25 kg/m2, is approximately
10-12% at aged 18 years but increases to 20-25% at aged 23 years. However,
the critical period for excessive weight gain is considered to be late
adolescent/early adulthood . Therefore, although 10% of 18 year olds
may well be overweight, it is unlikely that a similar percentage of five-
year-olds will be.
There are difficulties associated with the interpretation of BMI in
childhood, which is dependent on not only on height but also on gender and
pubertal status . Moreover, a recent report comparing BMI cut off
values with percentage body fat in prepubertal children found that
although high cut off points had high specificity the sensitivity was poor
and gender dependent .
Body mass index charts, standardised at an agreed level, are
undoubtedly useful for monitoring trends in fatness . It is unlikely,
however, that BMI in itself can provide a standard definition for
overweight and obesity in children that would be useful in clinical
Wessex Growth Study,
1. Cole TJ, Bellizzi MC, Flegel KM, Dietz WH. Establishing a standard
definition for child overweight and obesity worldwide: international
survey. Br Med J 2000; 320: 1240-1243.
2. Cole TJ, Freeman JV, Preece MA. Body mass index reference curves for
the UK, 1990. Arch Dis Child 1995; 73: 25-29.
3. Power C, Lake JK, Cole TJ. Measurement and long-term health risks of
child and adolescent fatness. Int J Obesity 1997; 21: 507-526.
4. Bini V, Celi F, Berioli MG, Bacosi ML, Stella P, Giglio P, Tosti L,
Falorni A. Body mass index in children and adolescents according to age
and pubertal stage. Eur J Clin Nutr 2000; 54(3): 214-218.
5. Reilly JJ, Savage SA, Ruxton CH, Kirk TR. Assessment of obesity in a
community sample of prepubertal children. Int J Obes 1999; 23(2): 217-219.
6. Voss LD, Mulligan J. Child obesity and body mass index. Lancet 1999;
Competing interests: No competing interests