Individual development and potential determinants of excess weight in children and adolescents: a longitudinal study

Excess body weight is a major public health concern already at a young age. The aim of this study was to track weight status among pupils aged 6-14 years in the City of Zurich, to examine the association between sociodemographic and environmental factors and excess weight at school entry and excess weight gain thereafter.

Longitudinal study.

Data were from the medical examinations routinely performed at public schools in Zurich, the largest city in Switzerland. Weight and height were measured in kindergarten (mean age: 5.9 years), grade 1 (7.2 years), grade 4 (10.1 years) and grade 8 (14.2 years).

The study included 7145 children who enrolled in kindergarten in 2003/04 or 2004/05 and had more than one measurement of weight and height.

Body weight and height were measured by physicians or nurses during the medical examinations at schools. For each measurement point, body mass index (BMI) was calculated and converted to the age- and sex-specific BMI z-scores and BMI percentiles. The stability of children's weight status categories, sociodemographic and environmental factors associated with excess weight gain and with overweight/obesity at school entry were investigated using multiple linear and logistic regression models.

The prevalence of overweight/obesity increased between kindergarten and grade 8 (from 17.6 to 26.0%). Overall, 86.2% of the children remained in the same weight category; 10.8% shifted to a higher and 3% to a lower category. There was a strong correlation between migration background and overweight/obesity at school entry (odds ratios between 1.62 and 3.42, all p <0.05). In addition, boys with Southern/Eastern European background (+2.29 BMI percentile, p = 0.023) and girls in lower level school type (+12.98 BMI percentile, p <0.001) had the highest risk for excess weight gain over a school period.

Overweight/obesity developed prior to school entry and mostly persisted through childhood. In order to better exploit obesity prevention potential, measures to prevent the development of the excess weight need to be implemented at a very early stage in life.