Tracking relative weight in subjects studied longitudinally from ages 3 to 13 years

Abstract

Heights and weights of a large sample of subjects studied longitudinally from ages 3 and 13 years were used to calculate relative weight, using a Body Mass Index score (BMI) which estimates adiposity. Males and females differed significantly in BMI scores only at ages 3 and 13 years. The correlations between BMI scores at all ages were positive and significant. The subjects were divided at each age into a 'light', an 'average' and a 'heavy' group based on the position of their BMI score relative to the 25th and 75th percentiles. Subjects were 'tracked' from ages 3, 7 and 11 years to determine whether they had remained in the same BMI group by age 13 years relative to their peers. Slightly fewer than half of the 3 year old subjects but the majority of 7 and 11 year old subjects remained in the same relative weight group by age 13 years. Only 1% of 7 and 11 year old subjects in the top and the bottom quartiles for BMI scores shifted from one extreme group to the other. Relative weight at 3, 7 and 11 years was more persistent for subjects with extreme bodyweights than subjects with bodyweights in the middle range. Consistent with the pattern of correlations, the tracking pattern for all 3 groups showed that subjects' BMI scores remained more stable as the subjects grew older.