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

Abstract

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.

Keywords::

• Child obesity
• longitudinal study
• BMI
• school-based study

Acknowledgements

We thank Professor Tim Cole for critical review of the manuscript and advice on statistical analysis. We also thank Professor Takao Takahashi for continued support.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.