"Problems expressing anger can translate into eating disorders and increased weight, which leads to a high risk of cardiovascular disease at a young age," said William H. Mueller, Ph.D., lead author of the study and professor of behavioral science at the University of Texas Health Science Center at Houston, School of Public Health.
In the mid-1990s, investigators at the university conducted a pilot study in which they found a strong association between body mass index and internalized anger in teen-agers. The association was stronger in girls than in boys.
Project HeartBeat! is a longitudinal study of children aged 8 to 18 that observes the development of cardiac structure and function in adolescence. As part of the study, Mueller and colleagues followed the eldest children -- a group of 160 (14 to 17 year-olds) -- for three years. Most were white; about 20 percent were black.
Researchers measured body mass index (BMI), obtained by dividing height squared by weight, at baseline and during the study period. The teenagers also completed the State-Trait Anger Expression Inventory (STAXI) to gauge anger levels, which measured "anger-in," "anger-out," "anger control" and "anger expression."
"Anger in" is not expressing feelings out of fear of what other people will think, Mueller said. "Anger out" is yelling, slamming doors and other aggressive behaviors. The "anger control "score measured the level of maturity and healthy expression of feelings. The "anger expression" score is calculated by adding the "anger in" score with the "anger out" score and dividing that number by the "anger control" score.