NEW YORK - Children who are overweight when they start school are far more likely to be obese by the time they become teenagers, according to a new study of nearly 8,000 children.
Overweight five-year-olds were four times more likely to be obese by age 14 than children who started kindergarten at a healthy weight.
Overall, 27% of kids in the study were overweight or obese when they started school and that ratio increased to 38% by eighth grade.
"Half of childhood obesity occurred among children who had become overweight during the preschool years," researchers led by Solveig Cunningham of Emory University in Atlanta wrote.
"If we're just focused on improving weight when kids are adolescents, it may not have as much of an impact as focusing on the preschool-age years," Cunningham told Reuters Health. The study "doesn't tell us what to do about it, but it helps tell us when we need to think creatively about what to do."
"I think it will make pediatricians a little bit more conscious of helping families and parents with weight-related problems early," said Dr. Ihuoma Eneli, medical director at the Center for Healthy Weight and Nutrition at Nationwide Children's Hospital in Columbus, Ohio.
"If we can help the child not become overweight by age five, their chances of becoming obese are so much lower," Eneli, who wasn't involved in the new research, told Reuters Health.
Research has shown that the rate of childhood obesity rose from about 4% in the early 1960s to more than 15% by 2000. Most of that research was done in adolescents.
"However, since many of the processes leading to obesity start early in life, data with respect to incidence before adolescence are needed," the researchers noted in the New England Journal of Medicine.
The new data came from the Early Childhood Longitudinal Study conducted by the U.S. National Center for Education Statistics. Children's weight and height were measured seven times between 1998, when they were in kindergarten, and 2007.
The obesity rate rose most rapidly between first and third grades - from 13% to almost 19%. The rate did not increase significantly between fifth and eighth grades.
About 32% of kids who were overweight when they entered kindergarten had become obese by age 14. That compared to 8% of normal-weight kindergarteners.
Between kindergarten and eighth grade, the prevalence of obesity rose by 65% among white children and 50% among Hispanic children. It more than doubled among black children.
Among kids from the wealthiest families, roughly 7% were obese in kindergarten and 11% by eighth grade.
Well-off children "are not immune," said Eneli.
Among the less-wealthy, obesity rates were much higher. When the researchers looked at the poorest children, they found 14% were obese in kindergarten and 24% in eighth grade.
Cunningham said having a normal weight in kindergarten did not guarantee that obesity would stay away. "Half of obese eighth graders do start out at normal weight," she said.
"Even birth weight may be associated with obesity risk," Cunningham added.
While roughly 11% of babies born weighing 8.8 pounds or less were obese by kindergarten, the rate was almost 23% for those born weighing more. By eighth grade, about 20% of children born with low or normal weights were obese and just over 31% of children with high birth weights were obese.
"My message for parents is always the same," said Eneli. "Try to feed your kids in a healthy way, build a healthy relationship with food and recognize that there isn't an age that's too young to teach them healthy lifestyles."