Increasing the amount of time schoolchildren spend in gym class reduces the probability of obesity, particularly among boys, reports a new Cornell study.

The study represents some of the first evidence of a causal effect of physical education (PE) on youth obesity and is forthcoming in the Journal of Health Economics.

An early, online version of the study, “The Impact of Physical Education on Obesity Among Elementary School Children,” is available.

The research offers support for the recommendations of organizations such as the Centers for Disease Control (CDC), Institute of Medicine and the American Academy of Pediatrics, all of which have advocated increasing the amount of time that elementary school children spend in gym class, says lead researcher and Cornell professor of policy analysis and management John Cawley, who conducted the study with Chad Meyerhoefer of Lehigh University, Ph.D. ’02, and David Frisvold of Emory University.

Treating variation in the amount of time that states mandate schoolchildren spend in PE as natural experiments, the researchers analyzed data from the Early Childhood Longitudinal Study, Kindergarten Cohort (1998-99) conducted by the National Center for Educational Statistics of the U.S. Department of Education. They found that an additional 60 minutes per week of PE time (enough to bring states without an explicit requirement up to the amount of PE time recommended by the CDC) reduces the probability that a fifth-grader is obese by almost 5 percent.

The researchers also detected a gender difference: Additional PE time reduces weight for boys but has a negligible effect for girls. One explanation for this difference, says Cawley, is that PE and other types of physical activity are complements for boys (increased PE leads boys to be more active in structured physical activities like organized sports), but substitutes for girls (increased PE leads girls to spend less time in organized sports and playground activities and more time watching television).

“We find no evidence that increased PE time crowds out time in academic courses or has spillovers to achievement test scores,” Cawley says.

The study was funded by the Robert Wood Johnson Foundation, Emory Global Health Institute, Cornell Institute on Health Economics, Health Behaviors and Disparities and a Faculty Research Grant from Lehigh University.