Application of Body Mass Index According to Height-Age in Short and Tall Children

et al. (2013) Application of Body Mass Index According to Height-Age in Short and Tall Children. PLoS ONE 8(8): e72068. doi:10.1371/journal.pone.0072068 Application of Body Mass Index According to Height-Age in Short and Tall Children Marjolein Bonthuis 0 Kitty J. Jager 0 Ameen Abu-Hanna 0 Enrico Verrina 0 Franz Schaefer 0 Karlijn J. van 0 Stralen 0 Reury F.P Bacurau, University of Sao Paulo, Brazil 0 1 European Registry for Paediatric Nephrology/ERA-EDTA Registry, Department of Medical Informatics, Academic Medical Center, University of Amsterdam , Amsterdam , The Netherlands , 2 Department of Medical Informatics, Academic Medical Center, University of Amsterdam , Amsterdam , The Netherlands , 3 Department of Pediatric Nephrology, Gaslini Children's Hospital , Genoa , Italy , 4 Department of Pediatric Nephrology, University Children's Hospital , Heidelberg , Germany Background: In children with either delayed or accelerated growth, expressing the body mass index (BMI) to chronological age might lead to invalid body composition estimates. Reference to height-age has been suggested for such populations; however its validity has not been demonstrated. Methods: Anthropometric data of healthy children were obtained from the German KiGGS survey. We selected three samples with different height distributions representing short stature (mean height SDS: -1.6), normal stature (height SDS: 0), and tall stature (height SDS: +1.6), and compared BMI-for-age and BMI-for-height-age between these samples across the paediatric age range. Differences between samples were tested using Kruskal-Wallis one-way analysis of variance and permutation tests. Results: At a given age, BMI was distributed towards lower values in short, and towards higher values in tall subjects as compared to a population with average height distribution. Expressing BMI to height-age eliminated these differences in boys with a short stature from 4 years to 14 years of age, in tall boys from 4 to 16 years, in short girls aged 2-10 years or tall girls aged 2-17 years. Conclusion: From late infancy to adolescent age, BMI distribution co-varies with height distribution and referencing to height-age appears appropriate within this age period. However, caution is needed when data about pubertal status are absent. - Funding: The ESPN/ERA-EDTA registry is funded by the European Renal Association and European Dialysis and Transplant Association (ERA-EDTA) and the European Society of Pediatric Nephrology (ESPN), and the European Agency for Health and Consumers of the European Commission (grant no. ESPNFY_2013). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: Amgen awarded a 10,000 grant to the European Society for Pediatric Nephrology (ESPN) to assist the start of the ESPN/ERAEDTA Registry. This does not alter the authors adherence to all the PLOS ONE policies on sharing data and materials. The global childhood obesity epidemic and the associated cardiovascular burden in later life increase the need for a valid measure of childhood adiposity [1]. Ideally, adiposity should be defined based on body fatness, but such measurements are usually unfeasible both in clinical practice and in epidemiological studies [2]. Instead, the body mass index (BMI) is a straightforward measure of the weight-forheight ratio that is applicable throughout human lifespan [3]. In children, BMI is dependent on age, sex, and sexual maturation, and is therefore expressed as standard deviation scores (SDS) using age- and sex specific reference values [4]. When linear growth and/or maturity are affected by chronic illness (e.g. chronic kidney disease (CKD), Turner syndrome, or Marfan syndrome) the relationship between age, height, and sexual maturation may be altered. This might lead to an underestimation (in short children) or overestimation (in tall children) of the BMI compared to peers of the same chronological age [5]. Therefore, it has been suggested to express the BMI according to height-age (i.e. the age at which a childs given height would be at the 50th percentile) in short children [6]. Furthermore, the BMI of healthy tall children was found to be higher than the BMI of shorter children, yielding systematically higher overweight prevalence estimates among taller children [7,8]. These findings question the validity of referencing BMI to chronological age without accounting for relative height. A recent study suggested that in children with CKD from 5 years up to adolescent age the BMI-for-height-age reflected physical development in the same way as BMI-for-age did in healthy children [9]. Therefore, it was concluded that BMI-forheight-age is the preferred method in childhood CKD. Although BMI-for-height-age might be an appropriate indicator of nutritional status in such children, information on the validity of the height-age approach over the entire childhood period, including pubertal and post-pubertal phase, and on its generalizability to tall populations is lacking. Therefore, we studied a large sample of healthy children to explore the impact of relative body size on the distribution of BMI-for-age and BMIfor-height-age across the paediatric age range. Subjects Anthropometric data were obtained from the German Health Interview and Examination Survey for children and adolescents (KiGGS) [10]. The sample has been described in detail elsewhere [11]. In summary, KiGGS is a cross-sectional nationally representative survey of 17 641 healthy German children aged 0.25-17 years conducted between May 2003 and May 2006. KiGGS used a two-stage sampling strategy. First, a sample of 167 communities, representative for community type and size in Germany, was drawn, followed by a random selection of equally sized cohorts of children per birth year from local population registries [11]. The survey involved selfadministered questionnaires, physical examinations and tests, as well as a computer assisted personal interview performed by a physician. Standardized height and weight measurements were performed by trained staff members. Children with medical conditions (e.g. premature birth (only 0-1 year olds), severe infections (only 0-1 year olds), and chronic diseases) or the intake of medication (e.g. growth hormone, corticosteroids) possibly affecting growth were excluded [12], therefore, short stature children will most likely have idiopathic short statures. Due to the small number of available children younger than 1 year of age the current analysis was restricted to children aged 1-17 years, resulting in a sample of 16,564 children. Definition of variables Height SDS was calculated as follows: SDS = (individual patient values mean values for age and sex-matched healthy peers)/SD values for age and sex-matched healthy peers [13]. BMI was calculated as weight/height2 and referred to either chronological age (BMI-for-age) or height-age (BMI-for-he (...truncated)