I read with interest the recent editorial on obesity in children in developing societies( I). I would like to offer the following comments with particular emphasis on utility of body mass index (BMI) in children.
Weight adjusted for height provides a simple measure of fatness. A very
flexible index of overweight is provided by the power function of weight/height, where n, the power of height usually takes the values in the range of I to 3. Readjusting it to the whole numbers, the value for n which best adjusts weight for height and at the same time removes most of the trend of increasing weight with age is
2(2,3). This leads to BMI, also known as
Quetlet index or Kaup index.
Adult BMI increases slowly with age so that the age independent cut-off values can be used to grade obesity. In children, however, BMI changes substantially with age, rising steeply in infancy, falling during preschool years and then again rising into adulthood(4). Because they have not long been available, child BMI charts are relatively untried in clinical practice.
Ratios of weight relative to height such as BMI may be used as an indirect measure of obesity and correlated with the more direct measure of adiposity(5). Measurement of skin fold thickness provides an estimate of cutaneous fat distribution which correlates well with BMI(4). BMI can be used as an index of overweight in children and is more easily obtained than skin fold thickness(6).
Changes in BMI in early childhood are similar for males and females(6,7). A study
on standardized percentile curves for BMI for children and adolescents observed that 5th to 75th centile values of BMI varied by less than 0.5 kg/meter square between boys and girls from 1 to 14 years of age. At upper centiles (90th and 95th) from age 6 to 14 years, values for females exceeded those for males by more than 0.5 kg/ meter square. The absence of large differences for BMI for
males and females at each age may be due to the higher correlation of BMI with total body fat than percentage of body fat(8). In the Child and Adolescent Trial for Cardiovascular Health (CATCH study), no difference in the BMI values between boys and girls were ob- served(9).
Evidence are accumulating to strengthen the association of obesity with
cardiovascular risk factors. These risk factors have been shown to
cluster in children and clustering in- creases with age(9,1O). In
children measures of blood pressure, fasting triglycerides and insulin
were significantly correlated with BMI and this relationship was most
pronounced among children whose BMI was above the 75th centile(1l).
With the control of common infectious diseases and emphasis being given
for prevention of coronary heart disease with measures to reduce risk factors in childhood itself, I feel it is high time we all adopt BMI as an age-independent anthropometric data universally and as a routine in children.
Department of Pediatrics,
Visakhapatnam 530 005,
Shetty PS. Obesity in children in developing societies: Indicator of economic progress
prelude to a health disaster? Indian Pediatr 1999; 36: 11-15.
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