Children who were overweight when entering kindergarten in 1998 in the United States were 4 times as likely as their normal-weight classmates to become obese by age 14 years, according to an article published in the January 30 issue of theNew England Journal of Medicine.
Almost half (45.3%) of obesity cases that developed between kindergarten and eighth grade occurred among the 14.9% of children who were overweight when entering kindergarten in 1998. "The annual incidence of obesity during kindergarten among these children was 19.7%, as compared with 2.4% among children who entered kindergarten with normal weight," write Solveig A. Cunningham, PhD, from the Hubert Department of Global Health, Emory University, Atlanta, Georgia, and colleagues.
The authors analyzed data from the Early Childhood Longitudinal Study, Kindergarten Class of 1998-1999, a nationally representative database with information on 7738 children who entered kindergarten in 1998 and were followed-up through 2007.
The researchers estimated the annual incidence of obesity during the 9 years according to sex, socioeconomic status, race/ethnicity, birth weight, and kindergarten weight. They used Centers for Disease Control and Prevention thresholds to define obesity and overweight by body mass index quintile.
When the children entered kindergarten at a mean age of 5.6 years, 12.4% were obese and 14.9% were overweight. By eighth grade, at a mean age of 14.1 years, 20.8% were obese and 17.0% were overweight. Most of the occurrence of obesity, however, occurred in early grades, and the annual incidence of obesity declined from 5.4% during kindergarten to 1.7% between fifth and eight grades.
The researchers defined incidence as the occurrence of new cases of obesity in children not previously obese, as compared with prevalence, the proportion of all children in each age group who were obese. Understanding incidence "helps us identify the ages of vulnerability and to identify the groups at greater risk. It's a bit of [a] different perspective on how obesity affects us and on where we might want to focus," Dr. Cunningham told Medscape Medical News.
"Among the kids who would become obese by the time they were middle-schoolers, most of that happened early on in elementary school. That helps us focus on these early years of kindergarten, first, second, and third grade, when a lot of obesity may actually occur."
"Those kids who came to kindergarten already overweight had about 4 times greater risk of becoming obese during the subsequent years," Dr. Cunningham said. "That tells us that some component of the risk of obesity may be set in motion by the age of 5 already. Kids who were born large and overweight at entry to kindergarten were at the highest risk of obesity."
In an accompanying editorial, Steven L. Gortmaker, PhD, from the Harvard School of Public Health, and Elsie M. Taveras, MD, MPH, from Massachusetts General Hospital, both in Boston, write that the new study "adds clear evidence" to previous research that early excess weight is a key risk factor for obesity.
"Given the limited evidence for effective treatment of obesity among children under 6 years of age, the limited resources of most clinical settings, and the limited predictive value of the 95th percentile of [body mass index], severe obesity may be a more useful cutoff for referral to more intensive, multidisciplinary treatment," they write.
"[W]ide-reaching, cost-effective policy and programmatic changes aimed at improving nutrition and physical activity among broad populations of children are key if we are to reduce early childhood weight gain and the risk of incident obesity throughout childhood."
This research was supported by a grant from the Eunice Kennedy Shriver National Institute of Child Health and Human Development. The authors and editorialists have disclosed no relevant financial relationships.