“Half of childhood obesity occurred among children who had become overweight during the preschool years,” the scientists wrote recently in the New England Journal of Medicine.
And as kids got older, their chances of becoming obese fell.
The researchers set out to track not the prevalence, but the incidence of childhood obesity, about which they said little is known. That is, they wanted to know the rate at which new cases of obesity occurred in children ages 5 to 14 in an effort to get at effective interventions.
“Emerging from the finding that a substantial component of childhood obesity is established by the age of 5 years are questions about how early the trajectory to obesity begins and about the relative roles of early-life home and preschool environments, intrauterine factors and genetic predisposition,” the researchers wrote.
In an accompanying editorial, Steven Gortmaker of the Harvard School of Public Health and Elsie Taveras of Massachusetts General Hospital wrote that the study should lead to some ideas about interventions to prevent obesity, with evidence pointing to ideas “that focus on children’s environments and that aim to alter early life systems” as probably the most effective.
The researchers, from Emory University, looked at 7,738 children who went to kindergarten in 1998 and were studied over the years through the Early Childhood Longitudinal Study. The results, they said, were consistent with other national studies.
When they started kindergarten, 12.4 percent of the children were obese; an additional 14.9 percent were overweight. In eighth grade, 20.8 percent were obese, 17 percent overweight.
The annual incidence of obesity decreased from 5.4 percent in kindergarten to 1.7 percent from fifth through eighth grade, the study showed.
They looked at some characteristics of the children who were overweight or obese as well.
Though they found no difference between children with a low birth weight and those with a normal birth weight, they found that babies born with a high birth weight (more than 4,000 grams, or about 8.8 pounds) had a significantly higher prevalence of obesity.
Wealthy children – those from the wealthiest 20 percent of families – had a lower prevalence of obesity in kindergarten than the other children.
The highest prevalence was among the children in the second-poorest 20 percent – with nearly 26 percent of them becoming obese by eighth grade.