A Prediction Equation for Total Body Water in Spanish Children.

Abstract

Total body water (TBW) is the largest molecular body compartment and comprises 73.2% of fat free mass (FFM). Accurate TBW measurements are fundamental for body composition estimations, although assessing TBW with accuracy is difficult and expensive, which make non-reference methods important to apply in epidemiological and clinical settings. Accurate and reliable predictive equations to determine TBW in children are lack, and we are unaware of specific equations developed for young Spanish population. Moreover, development of accurate tools to assess body composition in children is a cornerstone in the context of pediatric obesity. PURPOSE: The aim of this study was to develop a child-specific TBW prediction equation in Spanish children, aged 12 to 18 yrs, using the isotope dilution technique as the reference method. METHODS: Sixty-two healthy boys participated in this study (age 14.8 ± 1.9, stature 168.6 ± 9.0 cm, weight 65.5 ± 16.2 kg, and BMI 22.8 ± 4.4 kg.m−2). The selected independent variables were: girths and skinfolds measures (performed using the traditional protocols) and TBW obtained using a non-reference method [(bioelectrical impedance analysis (Medisystem, Sanocare Human System SL, Spain)]; whole body resistance (R) and reactance (Z) were assessed, then the impedance index was derived (ht2/R). TBW from the reference method was the dependent variable, and was obtained by deuterium dilution (D2O-TBW) using a stable Hydra gas isotope ratio mass spectrometer (PDZ, Europe Scientific, UK). Stepwise regression analysis was applied to identify the variables that most accurately estimated TBW. Twenty three boys were used to cross-validate the previous derived equation. Statistical significance was set at p<0.05. RESULTS: A new TBW prediction equation was developed for young Spanish children. The best equation incorporated ht2/R and weight (R2 = 0.91; SEE= 2.0 kg). The pure error was 1.03 kg. TBW (kg) = 0.495 ht2/R + weight x 0.107 + 6.08. CONCLUSIONS: In the present report, we derived and validated anthropometric predictive equation, which demonstrated to be accurate and reliable in healthy young male Spanish population. These equations may be used for accurate epidemiological studies in this specific population.