Since the 1990s, the United States has seen an alarming increase in childhood obesity rates. In 2012, 21 percent of all American children are obese. While adult obesity rates have doubled since 1980, from 15 to 30 percent, childhood obesity rates have more than tripled. Rising obesity rates have significant health consequences, contributing to increased rates of more than 30 serious diseases.
Researchers in both the U.S. and the U.K. have become progressively interested in how obesity might affect students' academic achievement, says John Reilly, specialist in the prevention of childhood obesity at the University of Strathclyde, and the study's lead author. Reilly says few studies have examined the same students over several years, or been able tease out obesity's effects from the influence of social factors, such as socioeconomic status.
The current study analyzed data from nearly 6,000 adolescent students in the U.K., comparing their body mass index from ages 11 to 16 with how well they performed in standardized tests during those years. About 71 percent of the students surveyed were of a "healthy weight" at the start, the researchers said, and about 15 percent were obese.
The academic exams, which tested the students' English, math and science abilities, were given three times at ages 11, 13 and 16. After adjusting for factors like socioeconomic status, IQ and menstruation cycles, the researchers found that, on average, girls who were obese at age 11 performed worse at age 11, 13 and 16 than girls deemed to have a healthy weight. Being obese at 11, the scientists found, was enough "to lower average attainment to a grade D instead of a grade C," by age 16.
Though the study followed British teens, Reilly says the findings are likely also applicable to students in the United States, where the proportion of children between the ages 12 and 19 who are obese grew from 5 percent in 1980 to nearly 21 percent by 2012. "The similarities between the environment, the culture, [and] school systems between the U.S. and the U.K. are more similar than may be obvious," Reilly says.
"There is nothing about this [study] that is specific to the U.K.," agrees David Katz, the director of Yale University's Prevention Research Center, who wasn't involved in the study
"Girls are much more affected by obesity in terms of mental health and well-being than boys are," he says, adding that stigma's negative effect on things like self-image, self-esteem and even depression may be lead girls to skip school more often, leading to poorer grades.
"The issue with girls," Katz says, "is that they're much more subject to the peer pressure and ridicule associated with obesity."
Learn more about the research and read the full report here.