Children who were obese scored lower on math tests than their peers of normal weight, a new U.S. study suggests.

Obesity during childhood and the teen years tracks into adulthood, increasing the risk of heart disease and Type 2 diabetes.

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Obesity that lasts throughout grade school can harm children's social and emotional well-being and academic performance. (Ted S. Warren/Associated Press)

Now researchers have followed 6,250 children from kindergarten through fifth grade and found that those who were obese over that time scored lower on math tests than non-obese children.

At five points in the study, parents gave information about their families such as income, teachers reported on the children's interpersonal skills and emotional well-being, and children were weighed and measured and  took academic tests.

In children who started with kindergarten with weight problems, differences in math performance started in first grade and lasted through fifth grade, the researchers said in this week’s issue of the journal Child Development.

"Our study suggests that childhood obesity, especially obesity that persists throughout the elementary grades, can harm children's social and emotional well-being and academic performance," the study's lead author, Sara Gable, an associate professor of nutrition and exercise physiology at the University of Missouri-Columbia, said in a release.

The association between obesity and test scores was weaker — or nonexistent, in the case of boys — if the children became obese in the third or fifth grade, rather than kindergarten.

Overall, the findings fit in with other studies suggesting a link between student obesity and academic achievement.

Social skills suffer

Obese students generally showed more emotional difficulties than their non-obese counterparts, and obese girls showed poorer social skills.

"It is possible that children with weight problems do more poorly in school because their social skills and peer relationships are compromised," the  study's authors wrote.

"Determining how teachers and other adult caregivers, including parents, respond to children's weight problems is relevant to obesity prevention and intervention efforts."

The researchers weren’t able to account for child puberty, which they called a limitation. Since the children were only followed to age 11, they weren’t able to tell whether academic performance suffered in higher grades.

They suggested further study to evaluate what else could affect weight and academic performance, such as poor sleep quality, asthma and diabetes that are associated with child obesity by interfering with the learning in class.