Secular trends in body composition for children and young adults: the Fels Longitudinal Study

To determine secular trends by birth decade in body mass index (BMI), waist circumference/height (W/Ht), percent body fat (PBF), and fat-free mass adjusted for height squared (FFM/Ht(2) ) in children and adolescents aged 8-18 years.

Serial data were analyzed from 628 boys and 591 girls aged 8-18 years who participated in the Fels Longitudinal Study. Subjects were stratified by birth decade from 1960 to 1999. Means and standard deviations were computed for all measurements by birth decade, age, and sex. A repeated-measures analysis of variance was used data to ascertain secular trends separately for boys and girls.

Boys and girls born in the 1990s had significantly higher mean BMI, W/Ht, and PBF than did children born in previous decades. Mean FFM/Ht(2) was significantly smaller in boys born in the 1990s than boys of the same age born in earlier decades. No secular trend was noted in FFM/Ht(2) in girls by decade of birth.

Our analysis of serial data collected over 4 decades confirms the secular trend in childhood BMI previously observed in successive cross-sectional studies. Our analysis discloses significant positive secular trends in W/Ht and PBF in both boys and girls and a significant negative secular trend in FFM/Ht(2) in boys over the last 4 decades of the 20th century. The secular changes presage increases in the prevalence of conditions associated with childhood and adolescent obesity-such as hypertension, glucose intolerance, and dyslipidemia-that may appear as early as the second decade of life.