While studies of adolescents and adults have found a link between weight and mental health, there have not been similar reports on young children. Psychologists guess that overweight children may have more behavioral problems and be more prone to depression than their peers, but no national studies have been done to support that theory. Two economists from the Rand think tank in California looked at the national data on kindergartners to see whether the link between mental health and weight in older people also held true for children.

What the researchers wanted to know: Do overweight children have more behavioral and mental health problems than their peers?

What they did: The economists used information from parents and teachers of kindergartners who participated in the Early Childhood Longitudinal Study, a national study of children run by the U.S. Department of Education. They asked parents and teachers about the kindergartners' behavior and moods, and compared that information with the children's height and weight. Because the study followed the same students for several years, the researchers also checked data from the same students several years later to see if being overweight in kindergarten predicted later behavioral problems. Overall, 9,949 children were included in the study, which began in the 1998–1999 school year.

What they found: About 11 percent of kindergartners were overweight in 1998. Overweight boys did not have more behavioral problems or worse moods than their peers, but it was a different story for the girls. In kindergarten, overweight girls were much more likely to be depressed and have behavior problems than other girls. Kindergarten teachers reported that overweight girls acted out, argued, and disrupted activities 81 percent more often than their peers did and acted lonely, anxious, and depressed 54 percent more often. Overweight girls seemed depressed 49 percent more often than normal-weight children, according to reports from parents. However, when overweight children who did not have behavior or mood problems in kindergarten grew older, they usually did not develop those problems over time. Kindergartners from low-income families or whose mothers were depressed were more likely to have later behavior problems, but weight seemed to have no effect.

What it means to you: This is one of the first studies to link weight with mental health in children as young as 5 years old. The study showed that, most likely before kindergarten, overweight girls already have more behavior and mental problems than their peers. While the results do not support the idea that weight can cause later behavior problems (caveats below), the authors argue that this study speaks to the importance of early interventions to prevent obesity in childhood.

Caveats: The authors do not fully accept that weight is not a predictor of later social and emotional problems, for several reasons. First, their study measured only major behavioral and mental problems—it did not capture more subtle issues (such as low self-esteem) that could arise from being overweight. Second, the study used a child's weight in kindergarten to predict behavior several years later; it did not take into account fluctuations in weight that often happen as children grow. Lastly, behavior or emotional issues could cause weight gain, not the other way around.

Find out more: The American Obesity Association has information about risk factors and identifying obesity in children.

For information about the data the researchers used, try the Early Childhood Longitudinal Study website

Read the article: Datar, A. and Strum, R. "Childhood Overweight and Parent- and Teacher-Reported Behavior Problems." Archives of Pediatric and Adolescent Medicine. August 2004, Vol. 158, No. 8, pp. 804–810.

Abstract online: http://archpedi.ama-assn.org