BMI z-score is the optimal measure of annual adiposity change in elementary school children

Background: BMI or BMI% adjusted for age has been identified as the optimal measure of short-term adiposity change in kindergarten children aged 29-68 months. The optimal measure of annual adiposity change in older age children, however, has not been determined. Aim: To identify the optimal measure of annual adiposity change for Japanese children aged 6-12 years. Subjects and methods: A cohort of 669 Japanese children in one private school in Tokyo in whom height and weight were measured annually between 6 and 12 years. Each child's annual variability in adiposity was summarized by the standard deviation (SD) of BMI and BMI% adjusted for age, BMI z-score and BMI centile. The SDs were compared in overweight and non-overweight children and correlated with each child's baseline BMI z-score. Results: The within-child BMI, BMI% and BMI centile SDs were significantly different in overweight and non-overweight children, while the BMI z-score SDs were similar in the two groups. Furthermore, the within-child BMI, BMI% and BMI centile SDs were inversely correlated with baseline BMI z-score, whereas BMI z-score SDs were not, with the exception of measurements for grade 1-2 children. Conclusion: The BMI z-score is the optimal measure of annual adiposity change for elementary school children.