Body mass index has risen more steeply in tall than in short three year olds: serial cross-sectional surveys 1988-2003

Objective: To monitor the changing relationship between BMI and height in young children.Design: Annual cross-sectional surveys using health-visitor-collected routine data 1988-2003.Setting: Wirral, England.Participants: 50,455 children (49% female) each measured once at the age of 3 years.Main outcome measures: Weight, height and derived body mass index (BMI = weight/height2) adjusted for age and sex (British 1990 revised reference) using standard deviation scores (SDS).Results: From 1988 to 2003 mean BMI increased by 0.7 kg/m2 while mean height fell by 0.5 cm. Over the same period the weight-height correlation rose from 0.59 to 0.71 (P <0.0001) due to BMI increasing faster in the taller than the shorter children. Among the shortest 10% of children mean BMI rose by 0.12 (95% confidence interval -0.05 to 0.28) kg/m² as against 1.38 (1.19 to 1.56) kg/m² among the tallest 10%, a twelve-fold difference. Adjustment for age, sex, seasonality, birth-weight and deprivation did not alter the findings.Conclusions: Among 3-year-old children in Wirral, where BMI has been rising for 16 years, the largest increase in BMI has occurred in the tallest children while in the shortest BMI has hardly changed. Tall stature has therefore become important for child obesity. It suggests a drive to increasing adiposity in young children that involves both growth and appetite, with faster-growing and hungrier children now more exposed to the ‘obesogenic’ environment.