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Objectives 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/Ht2) in children and adolescents aged 8–18 years. Methods Serial data were analyzed from 628 boys and 591girls aged 8 to 18 years who participated in the Fels Longitudinal Study. Subjects were stratified by birth decade from 1960 through 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. Results 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/Ht2 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/ Ht2 in girls by decade of birth. Conclusion Our analysis of serial data collected over four 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/Ht2 in boys over the last four 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.

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Previous research has shown that childhood body size is associated with blood pressure in adulthood, and that early and rapid growth rates are correlated with adverse cardiovascular outcomes. Our objectives are to estimate associations between childhood body size growth parameters and adult blood pressure, and to examine the effect of early attainment of critical growth milestones on adult blood pressure, relative to normal or late attainment. Lifetime height and body mass index (BMI) measurements in childhood, and systolic blood pressure (SBP) and diastolic blood pressure (DBP) measurements in adulthood are taken from participants in the Fels Longitudinal Study. Childhood growth curves are estimated separately for stature and BMI using the Preece-Baines and third-degree polynomial models, respectively. Associations between the resulting parameter estimates and adult blood pressure are then examined using linear mixed models. Our findings show that the ages of achievement of the stature-based growth onset and peak velocity, as well as the age of achievement of the BMI-based adiposity rebound, are negatively associated with adult blood pressure, implying that early height or BMI growth can lead to increased blood pressure in adulthood. There were subtle differences in these relationships based on age and gender, and also between SBP and DBP. These results expand on the existing literature, showing that not only childhood body size, but also the timing of childhood growth can have a deleterious effect on adult cardiovascular health.