Background: To investigate individual longitudinal change of relative weight, overweight and obesity from age 5 to 25 years by gender.
Methods: A cohort was imbedded in four surveys conducted 1992/1993, 1995/1996, 1998/1999 and 2004/2005 in three areas in Germany. Twelve-year-follow-up of 2183 children initially aged 5-13 years at baseline. Main measurements are body mass index (BMI) and international obesity task force (IOTF)-cut point defined overweight and obesity. A special longitudinal random effects model for cohort data was applied, which uses age as meta-meter of follow-up time and takes age at study entry into account.
Results: BMI, overweight and obesity increases with linear and squared age. Girls have a significant higher growth rate than boys in BMI (BMI: 0.89 vs. 0.75 kg/m(2) per 1 year age increment), whereas there is no statistical significant gender difference for overweight [odds ratio (OR) = 1.08 per 1 year] or obesity (OR = 1.11 per 1 year). Longitudinal change rates of BMI vary substantially between individuals [95% reference range (beta +/- 1.96 x SD) for linear change per 1 year is -0.14 to 1.98 in females and -0.29 to 1.83 in males; the 95% range of quadratic change rates are -0.09 to 0.04 in females and -0.08 to 0.05 in males]. Moreover, a steeper increase in BMI over time is observed for children with a higher baseline relative weight.
Conclusion: Increases in BMI and the propensity of overweight and obesity follow a quadratic growth curve with the steepest increase before and during puberty. However, the substantial variability of relative weight gain within individuals indicate, that more research in individual change patterns is needed.