But contrary to popular belief, researchers found being overweight doesn't increase the risk of developing new behavior problems among both boys and girls during the early elementary school years.
Researchers say psychological problems are among the most serious consequences of being overweight during childhood. Overweight children who are teased or ridiculed may suffer from low self-esteem and poor social skills.
Despite these well-known problems, researchers say most studies on the relationship between overweight and mental health have focused on older children and adolescents.
"There has been considerable attention on overweight status recently, often under the assumption that this can cause psychological problems for children and prevent learning," write researcher Ashlesha Datar, PhD, and colleagues at RAND in Santa Monica, Calif. "However, our results show that overweight girls already have more behavior problems before kindergarten; therefore, focusing on mental health and overweight is important in the early years."
Weight-Related Behavior Problems Start Early
In the study, researchers looked at the relationship between overweight and behavior problems in young children as they entered kindergarten and whether they developed more problems over time.
Information on height, weight, and parent- and teacher-reported behavior problems were collected three times during the first two years of elementary school for nearly 10,000 children.
The study showed that about one in 10 kindergarteners was overweight when he or she started school in 1998. The percentage of overweight boys was slightly higher than girls (11.7% vs. 10.6%).
Researchers found that overweight boys were no more likely to have behavior problems at the start of kindergarten compared with non-overweight boys.
However, overweight girls were much more likely to have behavior problems, as reported by parents or teachers, at the beginning of kindergarten compared with girls who were not overweight.
Researchers say that may be at least partially due to other factors such as the fact that overweight girls were less likely to be white and more likely to have a family income of less than $25,000, have mothers with a high school diploma or less, have fewer siblings, come from single-parent families, and have a higher birth weight than their non-overweight peers.
In particular, overweight girls had an 81% increased risk in teacher-reported externalizing behavior problems, such as arguing, getting angry, or disturbing class. Overweight girls also had an about 50% increased risk of teacher- and parent-reported internalizing behavior problems, such as anxiety, feeling sad, and low self-esteem.
But Weight Doesn't Increase Risk of Developing Problems
When researchers looked at the risk of developing behavioral problems over time, they found no proof that being overweight increased the likelihood of developing new behavior problems in either boys or girls.
Instead, they found that low family income and having a mother who was depressed were much stronger risk factors for children developing new behavior problems by the end of the first grade.
For example, the odds of developing externalizing behavior problems during the first two years of school were three times greater for girls whose family incomes were in the lowest quarter compared with girls whose family incomes were in the highest quarter.
The results of the study appear in the August issue of the Archives of Pediatric & Adolescent Medicine.