A child's chances of being obese in fifth grade may be largely established by the time that child enters kindergarden, according to a new, national study.
The study, published in the New England Journal of Medicine on Wednesday, also found that kids who are overweight as 5-year-olds are four times more likely than their normal-weight counterparts to become obese by eighth grade.
Unlike prior obesity studies that have focused largely on prevalence -- or the percentage of people affected at a given time -- the new paper sheds light on what study researcher Dr. Venkat Narayan called the "natural history" of childhood obesity in the U.S.
It shows the early years may be critically important in establishing long-term patterns.
"Those children who are overweight at age 5 are at high-risk [for later obesity]," said Narayan, who is the Ruth and O.C. Hubert Chair of Global Health and Epidemiology with the Emory School of Public Health.
The study relied on government data on more than 7,700 participants, collected at various points over a nine-year span.
By the time they entered kindergarten, roughly 15 percent of the children in the study were considered overweight, while 12.4 percent were considered obese. By eighth grade, 17 percent were overweight, and 20.8 percent were obese.
Narayan noted that with each year of school, fewer new children were considered obese. The annual rate of new cases dropped from 5.4 percent during kindergarten to 1.7 percent between fifth and eighth grade, the researchers found. (The Centers for Disease Control and Prevention considers any child with a body mass index in the 85th percentile or above relative his or her age and sex to be overweight, while those with a BMI at or above the 95th percentile are considered obese.)
In an accompanying editorial, also published in the New England Journal on Wednesday, Steven Gortmaker and Elsie Taveras, independent researchers with the Harvard School of Public Health and Massachusetts General Hospital, agreed the new study highlights the importance of improving prevention efforts aimed at young children.
"The present results indicate that the lower the relative BMI of a given child at kindergarten entrance, the lower the risk of obesity by eighth grade," they wrote. "However, a child who is obese at kindergarten entrance has a 47 percent risk of being obese by eighth grade."
What is not yet clear is why weight at kindergarten is such a strong predictor for later childhood obesity.
"When exactly does the process begin? What are the contributors?" asked Narayan. "There are three or four areas we need to look at: Family lifestyle, diet and physical activity [is one]. Could it be maternal influences? A mother's nutritional status during pregnancy? Could it have paternal influences? All of these are questions that are wide open."
In the meantime, experts say the study should not unnecessarily alarm parents of overweight or obese children, but rather help them -- as well as educators, health care professionals and public health experts -- understand the potential significance of early childhood weight as it pertains to later health and well-being.
"While some very obese children do need to lose weight, the vast majority of children can 'grow into' their weight," Dr. Esther Krych, a pediatrician at the Mayo Clinic Children's Center who did not work on the new study, wrote in an email to The Huffington Post. "By slowing the rate at which a child gains weight, overweight children will 'lean out' gradually and can continue to grow appropriately."
Parents can help by sticking to the basics, she said: Replace TV time with family walks or active play; use time together, not food, as a reward; watch portion size and teach children to put healthy choices in the grocery cart; and model healthy stress-management skills. Public health efforts should focus on keeping pregnant moms healthy, and supporting their breastfeeding efforts, Krych said.
"Adopting wellness needs to happen all together as a family," Krych said.