Body mass index trend as a new parameter for evaluating children's nutritional status

Abstract

ObjectivesThe objective was to identify a body mass index (BMI) trend as a new indicator and predictor of children's nutritional status, replacing absolute BMI, and to demonstrate that a local BMI trend is more appropriate for this purpose than a national (or international) BMI trend. Study designAn entire school year group of primary school children were subject to a longitudinal 8-year cohort study. MethodsBMI was measured three times during primary school education—on enrolment to primary school, then in the fifth and eighth grades. The BMI values obtained were used to create gender- and age-based percentile curves for children born in 1998/1999 (Osijek Percentile Curves (OPC) study) in the Osijek-Baranja County, Croatia. Every BMI result obtained was linked to one of the five percentile ranks (PRs) according to threshold percentiles 3, 10, 90 and 97; hence, the PRs were <3, ≥3 to <10, ≥10 to <90, ≥90 to <97 and ≥ 97. Percentiles and PRs were specified for each BMI value in a dual fashion, i.e. according to OPC and the entire Croatian territory (Croatian Percentile Curves (CROPC)-2008) cross-sectional study. After integrating the BMI values at all three time points, two BMI trends appeared—one based on the OPC criteria and one based on the CROPC-2008 criteria. Individual trends were grouped into three descriptive BMI categories: ‘healthy’, ‘at risk’ and ‘unhealthy’. ResultsFor the OPC and CROPC-2008, the ‘healthy’ trend characterised 2097 (78.72%) and 1975 (74.14%) children, respectively; the ‘at risk’ trend marked 434 (16.29%) and 458 (17.19%) children, respectively; and the ‘unhealthy’ trend was found in 133 (4.99%) and 231 (8.67%) children, respectively. The biggest difference between the OPC-based and CROPC-2008–based results was detected in the ‘unhealthy’ trend. According to CROPC-2008, there were almost twice as many children in that category. For the purpose of study design and comparing results obtained based on OPC and those obtained based on CROPC-2008, the BMI of one boy was used. His BMI values on starting primary school, in the 5th and in the 8th grades were 19.05 kg/m2, 26.11 kg/m2 and 27.11 kg/m2, respectively. Analysis of PRs based on OPC and CROPC-2008 reveals that the same boy was represented by different trends: ‘<90 <90 <97’ and ‘<90 <97 <97’, respectively. In terms of residence, girls from urban areas have higher BMI values than rural girls when starting primary school. ConclusionThis study suggests that a BMI trend could be a better indicator and predictor of children's nutritional status than absolute BMI. In addition, a cohort study is preferential to a cross-sectional study as a trend in an OPC-based study can be personalised. Also, local BMI reference values defined for each generation of children are more advantageous in this context than national BMI reference values.