Now parents can tell their children an added benefit to being a good kid – growing up to have a healthier body weight.
Children who exhibit self-control at an early age have a lower body mass index (BMI) 30 years later, according to a study in the Journal of Pediatrics released Thursday.
Between 1968 and 1974, a group of 4-year-olds completed a delay-of-gratification test in which they were asked to wait to eat a treat such as a cookie or marshmallow that was placed in front of them. If they waited, they were told, they could earn a second treat.
Thursday's study, which was a follow-up study involving these very same study participants, who are now in their mid-30s, looked at the weight status of these subjects and compared that to their previous self-control abilities.
The researchers found that each minute a child delayed gratification predicted a 0.2-point decrease in adult BMI.
While experts agree that genetics, environment and personal responsibility all influence body weight, this study now shows that some of these factors may be evident much earlier in life.
"The environment exerts a huge influence, but how we interact with any given environment is also important," said Dr. David L. Katz, director of the Yale University Prevention Research Center. "It's interesting that the tendency is there in early childhood, suggesting it may be innate, or learned very early."
In fact, early personality traits are known to have long-lasting implications. Studies have shown that when children display a longer delay of gratification at preschool age, it is associated with beneficial outcomes such as "adolescent academic strength, social competence, planfulness [and] ability to handle stress," wrote Tanya R. Schlam, the study's lead author. "In some children, it was also associated with higher Scholastic Aptitude Test scores in adolescence and less illegal drug use in adulthood."
Though the findings discuss childhood levels of self-control, it does not necessarily mean that lack of restraint is the only cause for obesity. Rather, the discipline exhibited by these children may reflect a host of other environmental factors at play.
"Can one 'teach' a child to delay gratification, or is it related to innate personality characteristics?" asked Joanne P. Ikeda, nutritionist emeritus from UC Berkeley. "Just think of all the variables: parenting style and practices, physical activity habits, quality of the diet, child's self esteem, genetic predisposition, number of siblings and so on."
In fact, the study design, itself, may indicate that other factors are at play. The original experiment was conducted at Stanford University's world-renowned Bing Nursery School -- a preschool with plenty of children of Stanford faculty, and one of the premier nursery schools in the country. Even among the respondents, only 24.4 percent of the participants were overweight but not obese, and 9.1 percent were obese. In comparison, 34.2 percent of U.S. adults were overweight but not obese during the time of this study, and 33.8 percent were obese.
This indicates that other dynamics affect weight irrespective of children's level of self-control.
"The sample they are collecting from is a bit skewed," noted Dr. Stephen Cook, pediatrics fellow at Golisano Children's Hospital at the URMC. He added that within the sample, "they also seem very educated as adults."