Refined analysis of the critical age ranges of childhood overweight: implications for primary prevention.

Prevention-interventions would certainly benefit from a precise knowledge of the age range when the most pronounced increases in prevalence of overweight and obesity occur in the general population. Data of 15,662 subjects aged 2-18 years were obtained from a national representative health survey (German Health Interview and Examination Survey for Children and Adolescents (KiGGS)) conducted in Germany. Weight, height, and BMI z-scores were calculated relative to the UK 1990 reference, and prevalence of overweight and obesity was defined according to the IOTF (International Obesity Task Force) age- and sex-specific cut-offs. Univariate ANOVAs for overweight, obesity, weight, height, and BMI z-scores as dependent variables were employed to assess significant differences for these measures across various age levels. Significant analysis was followed by post-hoc comparisons using Bonferroni adjustments. The main effect of age was estimated using a multinomial logistic regression model, and by defining the first derivative of a polynomial spline function. Different eclectic slopes over the entire age range from 2 to 18 years have been observed. Prevalence of overweight substantially increases between the 5th and the 8th year (12.5-21.4%; P ≤ 0.001). Maximum increase of the polynomial fit was detected at 7.2 years. Our findings suggest a relatively narrow age range at the first school year when overweight in German children especially increases. We therefore propose that psychosocial correlates may be related to the general life-time event around the age of entering school.