Tracking of BMI in Japanese children from 6 to 18 years of age: Reference values for annual BMI incremental change and proposal for size of increment indicative of risk for obesity

Abstract

A large incremental increase in BMI indicates excess fat deposition in most children, but the reference values for identifying those at risk for developing obesity have not been defined. To determine the mean and SD of annual incremental change (ΔSDS) in BMI for Japanese school children. A cohort of 669 Japanese children in one private school in Tokyo in whom height and weight were measured annually between 6-17 years of age. Each child's BMI was converted to SDS as based on the 1978-1981 Japanese references for the 12 annual measurements to derive the correlation coefficient, r, between two successive measurements. Using the formula, SD of ΔSDS = √2(1-r), the mean and SD of ΔSDS were obtained. Excess BMI gain was defined in terms of ΔSDS in Japanese children. Annual incremental increase greater than 2 SD of ΔSDS, equivalent to 1-2 BMI units/year for younger children and 2-3 BMI units/year for older children, respectively, indicates rapid increase in body fat in Japanese children. Based on analysis of incremental change in BMI in this cohort, a cut-off has been identified that can be used to identify children at risk for developing obesity.