Differences in the physical growth of US-born black and white children and adolescents ages 2-19, born 1942-2002

Aim: The present study estimates differences in the trend and in die age-by-height profiles of US-born non-Hispanic black and white children and adolescents born 1942-2002. Subjects and methods: The combined NHES and NHANES data sets stratified by ethnicity and gender were used. The differences in height-for-age z-scores (HAZ) were decomposed into an age effect and a secular trend effect using a non-linear regression model. Results: The tempo of growth among blacks is faster than among whites. Black girls are more than 0.3 sigma taller than white girls between the ages of 3 and 11. At age 9 this amounts to some 2.7 cm. White boys catch up to black boys at age 14 and white girls catch up at age 15 and are taller thereafter. At age 19 whites are only slightly taller: By 0.12 sigma (0.8 cm) for boys and 0.03 sigma (0.2 cm) among girls. The cumulative effect of the differences in the secular trend is considerable. Between the birth cohorts of the mid-1950s and the beginning of the new century blacks gained some 0.17 sigma (girls) and 0.23 sigma (boys) relative to white HAZ values. Conclusion: Blacks have a faster tempo of linear growth in childhood partly on account of their nutritional habits, as girls in particular tend to have higher BMI values, and partly probably because of genetic differences.