First reference curves of waist circumference for German children in comparison to international values: the PEP Family Heart Study

Background: Waist circumference (WC) is a sensitive marker for abdominal obesity in the pediatric age group. However, WC is influenced by age, sex, ethnicity and body mass index (BMI), causing difficulties in the selection of the most appropriate cut-off value. Considering the lack of reference values in Germany, we developed age- and gender-specific WC smoothed reference curves in German children, and compared them with reference curves obtained from different countries. Methods: A representative sample of 3531 German children (1788 boys, 1743 girls) aged 3-11 years participating in the Prevention Education Program (PEP) Family Heart Study was studied. WC was measured according to the recommendations of the World Health Organization, then age- and sex-specific WC reference curves were constructed and smoothed using the LMS method and SPSS 14.0 for statistical analysis. Results: WC increased with age in both boys and girls. Boys had higher values of WC than girls at every age and percentile level. 4.1% of the boys and 2.8% of the girls had WC values >97th percentile as compared to 6.3% of the boys and 4.9% of the girls with >97th percentile of BMI (severe obesity). 3.1% of the boys and 2% of the girls had both risk factors. Because 85.3% of the boys and 87.3% of the girls with WC<90th percentile had normal weight, this cut-off point might be appropriate for defining high WC. Conclusions: These first WC reference curves of German children can be added to the existing international curves for children; comparison of different populations demonstrated that the German values are in the middle range of the curves obtained in different countries. Our findings about significant differences between the reference curves obtained in various regions emphasize the necessity of developing population-specific percentiles, and to use them in clinical and epidemiological studies among children.