Body weight, body mass index, overweight and obesity in consecutive cohorts of children at school entry in a community in Lower Bavaria 1997-2002

Abstract

Objective: To study time trends of weight, body mass index, overweight and obesity of children at school entry and to analyze potential effects of changes in the structure of consecutive cohorts of children at school entry over time on these weight-related measures. Design: We studied height, weight and body mass index (BMI) in 6 consecutive cohorts (1997-2002) of children at school entry (N=6,420). Overweight and obesity were defined by internationally valid sex and age specific cut-off points. In addition to descriptive statistics for time trends we applied an analysis of covariance to estimate the impact of covariates on weight and BMI and logistic regression models for the impact of covariates on overweight and obesity. Results: Although we found an overall decrease of mean body weight (minus 9%), BMI (minus 9.5%), overweight (minus 7.4%) and obesity (minus 6.8%) between 1997 and 2002, there was a considerable variation in these measures between single years. The analysis of covariance showed significant impact of age, gender and year of examination on weight and BMI. Whereas there were significant differences in the proportion of overweight children between different age groups, the effect of age was not significant for the proportion of obesity. Multiple logistic regression models showed that age (OR, 2.8; 95% CI, 2.3-3.5) and female gender (OR, 1.3; 95% CI, 1.2-1.5) were significantly associated with overweight and significantly with obesity (age: OR, 1.8; 95% CI, 1.2-2.9; female gender: OR, 1.4; 95% CI, 1.0-1.99), respectively. In these models the years of examination of 1998 (OR, 1.9; 95 %CI, 1.5-2.5) and 1999 (OR, 2.5; 95% CI, 1.97-3.3) were significantly associated with overweight, and the year 1999 (OR, 2.9; 95% CI, 1.6-5.2) with obesity. Conclusions: Our study showed that changes in age and gender distribution have to be taken into account when time trends of weight, BMI, overweight and obesity are derived from investigations of children at school entry.