Tracking and Variability in Childhood Levels of BMI: The Bogalusa Heart Study

Objective Although the tracking of BMI levels from childhood to adulthood has been examined, there is little information on the within‐person variability of BMI. Methods Longitudinal data from 11,591 schoolchildren, 3,096 of whom were reexamined as adults, were used to explore the tracking and variability of BMI levels. This article focuses on changes in age‐adjusted levels of BMI. Results There was strong tracking of BMI levels. The correlation of adjusted BMI levels was r = 0.88, and 78% of children with severe obesity at one examination had severe obesity at the next examination (mean interval, 2.7 years). Further, an increase in adjusted BMI from +5 kg/m 2 (above the median) to + 10 increased the risk for adult BMI ≥ 40 by 2.7‐fold. However, BMI levels among children and adolescents were variable. Over a 9‐ to 15‐month interval, the SD of adjusted BMI change was 0.9 kg/m 2 , and 0.7% of children had an absolute change ≥ 3.5. This variability was associated with the interval between examinations and with the initial BMI. Conclusions Despite the high degree of tracking of BMI, annual changes of 3.5 kg/m 2 or more are plausible. Knowledge of this variability is important when following a child over time.