Body mass index has risen more steeply in tall than in short 3-year olds: serial cross-sectional surveys 1988-2003.

Objective: To monitor the changing relationship between body mass index (BMI) and height in young children.

Design: Annual cross-sectional surveys using health-visitor-collected routine data 1988-2003.

Setting: Wirral, England.

Participants: Fifty thousand four hundred and fifty-five children (49% female) each measured once at the age of 3 years.

Main Outcome Measures: Weight, height and derived BMI (weight/height(2)) adjusted for age and sex (British 1990 revised reference) using standard deviation scores.

Results: From 1988 to 2003, mean BMI increased by 0.7 kg/m(2), whereas 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) owing 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: -0.05-0.28) kg/m(2) as against 1.38 (1.19-1.56) kg/m(2) among the tallest 10%, a 12-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, whereas 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 fast growing and hungrier children now more exposed to the 'obesogenic' environment.