Body composition reference charts for UK infants and children aged 6 weeks to 5 years based on measurement of total body water by isotope dilution

Abstract

Background: Until recently, pediatric body composition reference data were very limited, hindering interpretation of measurements. In the last decade, such data emerged for several techniques for children ≥ 5 years, but equivalent data for younger age groups remain lacking, due to their poor compliance with most techniques.

Objectives: To provide reference data for use in clinical practice and research from 6 weeks to 5 years, that are based on measurements of total body water (TBW) by isotope dilution.

Design: The data on anthropometry and TBW were available from studies of 463 infants and children aged 6 weeks to 7 years, conducted between 1988 and 2010. Both breast-fed and formula-fed infants were included. TBW was measured by ²H- or ¹⁸O-labeled water, and converted to fat-free mass (FFM) using published hydration coefficients. Reference charts and SD scores (SDS) were constructed for FFM, fat mass (FM), FFM index and FM index for each sex, using the lambda-mu-sigma method.

Results: Both sexes were significantly heavier and longer than UK 1990 reference data (p < 0.01), but did not differ in body mass index SDS. Breast-fed infants were longer than formula-fed infants but did not differ in body composition.

Conclusions: These reference data will enhance the ability of clinicians to assess and monitor body composition and FFM/FM accretion in clinical practice in younger age groups. Total body water can be measured in most patients, though abnormalities of hydration must be addressed. However, the centiles do not overlap exactly with those published for older age groups, limiting comparability between younger and older children.

Fig. 1

Distribution of body mass index standard deviation score (BMI SDS) against age in the sample. N = 199 males, 233 females

Fig. 2

Centiles for total body water (TBW) in (a) boys and (b) girls, fat-free fat mass (FFM) in (c) boys and (d) girls, and fat mass (FM) in (e) boys and (f) girls measured by deuterium dilution. The 3rd, 10th, 25th, 50th, 75th, 90th and 97th centiles are displayed

Fig. 3

Centiles for (a) fat-free mass index (FFMI) in boys, (b) fat-free mass index (FFMI in girls, (c) fat mass index (FMI) in boys and (d) fat mass index (FMI) in girls. The 3rd, 10th, 25th, 50th, 75th, 90th and 97th centiles are displayed

Fig. 4

Published data of Fomon and colleagues [17] and Butte and colleagues [22] converted to z-scores using our new reference data, to evaluate differences between studies in (a) fat-free mass (FFM), (b) fat mass (FM), (c) fat-free mass index (FFMI) and (d) fat mass index (FMI)