Socio-demographic disparities in distribution shifts over time in various adiposity measures among American children and adolescents: What changes in prevalence rates could not reveal.

Background. While obesity prevalence in the US has been increasing, adiposity shifts may vary across socio-demographic groups, and various adiposity measures may reveal different patterns. Methods. To study changes over time in adiposity measures, distributional shifts in body mass index (BMI, kg/m(2)), BMI-percentile, waist circumference (WC) and triceps skinfold thickness (TST), and compare between-group differences, National Health and Nutrition Examination Surveys (NHANES) III 1988-94 and 1999-2004 from children aged 2-19 years old data were analyzed. Annual shift in adiposity measures across percentiles were shown as Tukey's mean-difference plots, with percentile-specific mean differences being divided by 10.5 years. Overall and quintile-specific adjusted shifts were estimated from multivariate ordinary least square (OLS) regression models. Results. Mean 10.5-year increases in adiposity were statistically significant, higher in older groups, more pronounced in some sex-ethnic groups (e.g., black girls) and at upper percentiles (more obese groups) for most measures and sex-age-ethnic groups. Adjusted increase in mean BMI was 0.60 in girls and 0.64 in boys; BMI percentile, 3.02 and 3.15 units; WC, 2.85 and 2.42 cm; and TST, 0.81 and 1.18 mm, for girls and boys, respectively. Ethnic, age and sex disparities in mean BMI became wider over time. Several significant ethnic differences in adjusted adiposity shifts within the lowest (Q1) and uppermost (Q5) quintiles of adiposity measure distributions were noted. Conclusions. The increase in adiposity among American children was unequally distributed across groups and varied across the spectrum of various adiposity measures. Overweight groups gained more adiposity over time, especially WC. Solely examining prevalence shifts masks pattern complexity.