Obesity from Childhood to Mid-adulthood in the United States: A Synthetic Cohort Approach to Measuring Health Trajectories.

BACKGROUND: Obesity dynamics early in life are likely important for long-term health, but have only been described piecemeal, because nationally representative longitudinal datasets are few and have limited follow-up duration. METHODS: We created a synthetic cohort by combining two US nationally representative datasets, the Early Childhood Longitudinal Study, Kindergarten Class of 1998-1999 (ECLS98; N = 21,120; ages 4-16 years; birth cohort 1991-1994), and the National Longitudinal Survey of Youth 1997 (NLSY97; N = 8,984; ages 12-41 years; birth cohort 1980-1984). We used the older-age cohort to impute future weight trajectories of children in the younger-age cohort by matching based on subject-level body mass index trajectories estimated via linear mixed models. We projected trajectories to age 41 years in 2035 for children observed up to a mean age of 13.5 years in 2007. RESULTS: The synthetic cohort (N = 10,102) showed that obesity prevalence increases from 10.0% at age 4 years to 56.3% at age 41 years. Obesity incidence peaks at ages 8 years (4.00/100 person-years [PY] [3.29-4.73]), 26 years (4.48/100 PY [3.04-5.92]), and 38 years (3.60/100 PY [0.00-8.91]). CONCLUSIONS: This synthetic cohort approach can be used to characterize dynamics of obesity and other conditions by maximizing data from shorter "life segments." Findings suggest that today's young adults will continue to become heavier as they age. In addition to prevention before kindergarten entry, other periods for obesity prevention could be middle childhood, mid-twenties, and late thirties.