Those efforts to fight obesity in schools? Think younger. A new U.S. study finds that much of a child's "weight fate" is set by age 5, and that nearly half of kids who became obese by the eighth grade were already overweight when they started kindergarten.
The prevalence of weight problems has long been known — about a third of U.S. kids are overweight or obese. But surprisingly little is known about which kids will develop obesity, and at what age.
Researchers think there may be a window of opportunity to prevent it, and "we keep pushing our critical window earlier and earlier on," said Solveig Cunningham, a scientist at Emory University. "A lot of the risk of obesity seems to be set, to some extent, really early in life."
She led the new study, which was published in this week's New England Journal of Medicine and paid for by the federal government.
It tracked a nationwide sample of more than 7,700 children through grade school. When they started kindergarten, 12 per cent were obese and 15 per cent were overweight. By eighth grade, 21 per cent were obese and 17 per cent were overweight.
Besides how common obesity was at various ages, researchers focused on the 6,807 children who were not obese when the study started, at kindergarten entry. Here are some things they found:
WHO BECAME OBESE: Between ages 5 and 14, nearly 12 per cent of children developed obesity 10 per cent of girls and nearly 14 per cent of boys.
Nearly half of kids who started kindergarten overweight became obese teens. Overweight 5-year-olds were four times as likely as normal-weight children to become obese (32 per cent versus 8 per cent).
GRADE LEVELS: Most of the shift occurred in the younger grades. During the kindergarten year, about 5 per cent of kids who had not been obese at the start became that way by the end. The greatest increase in the prevalence of obesity was between first and third grades; it changed little from ages 11 to 14.
RACE: From kindergarten through eighth grade, the prevalence of obesity increased by 65 per cent among whites, 50 per cent among Hispanics, almost 120 per cent among blacks and more than 40 per cent among others — Asians, Pacific Islanders and Native Americans and mixed-race children.
By eighth grade, 17 per cent of black children had become obese, compared to 14 per cent of Hispanics and 10 per cent of whites and children of other races.
INCOME: Obesity was least common among children from the wealthiest families and most prevalent among kids in the
next-to-lowest income category. The highest rate of children developing obesity during the study years was among middle-income families.
BIRTHWEIGHT: At all ages, obesity was more common among children who weighed a lot at birth — roughly 9 pounds or more. About 36 per cent of kids who became obese during grade school had been large at birth.
The study's findings do not mean that it's too late for schools to act, but their best tactic may be to focus on kids who are overweight and try to encourage exercise and healthy eating, Cunningham said.
The work also shows the need for parents, doctors, preschools and even day care centres to be involved, said Dr. Stephen Daniels, a University of Colorado pediatrician and a spokesman for the American Heart Association.
"You can change your fate by things that you do early in life," with more exercise and eating a healthy diet, he said. "Once it occurs, obesity is really hard to treat. So the idea is we should really work hard to prevent it."