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THURSDAY, June 14 (HealthDay News) -- Youngsters who are persistently overweight may not perform as well academically -- specifically in math -- as their normal-weight peers, new research suggests.
Although the study didn't find a direct cause-and-effect relationship between being overweight or obese and school performance, the researchers did find that children who started kindergarten carrying extra weight and were still heavy when they finished fifth grade performed worse on math tests.
"These children are not necessarily less smart, but they're performing less well," said the study's lead author, Sara Gable, an associate professor and state extension specialist in nutrition and exercise physiology at the University of Missouri, in Columbia.
Gable said she suspects interpersonal troubles and internalizing behaviors may be why weight can affect math performance.
"We know, in general, that children who have poor peer relationships don't do as well at school," she said. "And we also know that children with internalizing behaviors don't do as well. Internalizing behaviors are anxiety, worry, not feeling as if they have a lot of friends and feeling sad.
Children with weight problems tend to feel internalizing behaviors and not have good interpersonal skills," she added.
Gable said that these effects, year over year, are likely cumulative.
Nancy Copperman, director of public health initiatives at North Shore-LIJ Health System in Great Neck, N.Y., said the study demonstrates the importance of preventing childhood obesity.
"Obesity isn't just a cosmetic problem," she said. "It has impacts that go from chronic disease to mental achievement, and ultimately to income and a happy, successful, well-adjusted life."
Results of the study appear in the July/August issue of the journal Child Development.
For the study, Gable and her colleagues used data from the Early Childhood Longitudinal study. The current study included 6,250 youngsters from kindergarten through fifth grade. Weight and height were measured at five points throughout the study, and the measurements were used to calculate the children's body-mass index, a figure that assesses whether someone is normal weight, overweight or underweight.
The children were placed into one of three groups based on their weight: never overweight (80 percent of the children), persistently overweight (12 percent) or later-onset overweight (8 percent). The later-onset group was not overweight in kindergarten or first grade, but was overweight in third or fifth grade (or both).
At the time measurements were taken, parents and teachers filled out extensive questionnaires about the children. Teachers were asked to assess interpersonal relationships and internalizing behaviors. In addition, the children were given standardized math tests at each point.
The study group was slightly less than half male; most (83 percent) of the children lived in two-parent households; two-thirds of the children were white, 16 percent were Hispanic, 9 percent were black and 5 percent were Asian. Just less than half of the mothers worked full-time, and the average household income was about $50,000.
Children who were persistently overweight from kindergarten through fifth grade performed worse on math tests beginning in first grade. Weight status didn't play a significant role in math-test performance when the children were in kindergarten.
"That means there's some aspect in the school setting that's affecting performance," Gable said.
One factor may be a subtle bias the researchers found when teachers were asked to rate children's interpersonal skills and internalizing behaviors. Teachers were more likely to rate persistently overweight children as having internalizing behaviors than their never-overweight or later-onset peers.
With interpersonal skills, the teachers were more likely to rate persistently overweight girls as having trouble with their peers compared to their normal-weight or later-onset peers. No such difference was found for boys.
Gable said there are likely other factors at play. For example, obese children may miss more school days, which would affect their performance. Obese children also are more likely to have sleep apnea, which, if untreated, can affect daytime performance.
The bottom line, Gable said, is that "parents need to protect children from obesity as long as they possibly can. Establish a healthy lifestyle that prevents this from happening. Once someone is obese, it's really hard to change."
If your child already is overweight, Gable said, it is important to get them on a course to better habits. But, she added, it is also important to "help children learn that this is not who they are." Their weight doesn't define them.
It is also crucial that any changes to diet and exercise routine affect the whole family.
"The whole family's routines have to change. Not just one person's plate or one person's activity level," Gable said.
For her part, Copperman said, "It's never too late to start helping your child live a healthy lifestyle."
"It's kind of like driving a car on the expressway," she said. "You can't suddenly put the car in reverse. If your child is already overweight, you need to step on the brakes to stop the weight gain."
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