Causal Effect of Sleep Duration on Body Weight in Adolescents: A Population-based Study Using a Natural Experiment.

BACKGROUND: A large number of observational epidemiologic studies have reported consistent associations between short sleep duration and increased body weight, particularly in children and adolescents. Causal evidence on the effect of sleep duration on body weight is still limited, however. METHODS: This study exploits a unique natural experiment that can be argued to have increased sleep duration in an adolescent population in South Korea. In March 2011, authorities in three of the 16 administrative regions decreed restricting the closing hours of hagwon (private tutoring institutes) to 10 PM. Assuming this policy change is a valid instrument for sleep duration, it allows investigation of the causal effect of sleep duration on body weight in a difference-in-differences and instrumental variable framework. We used a nationally representative sample of 191,799 in-school adolescents in 7th-12th grades surveyed in the 2009-2012 Korea Youth Risk Behavior Web-based Survey. RESULTS: The policy change was associated with sleep extension and body weight reduction in a subset of general high school 10th-11th graders (around 10% of the sample) whose sleep duration would otherwise have not increased. The main results suggested that a 1-hour increase in sleep duration was associated with a 0.56 kg/m reduction in body mass index (95% confidence interval = 0.07, 1.05) and a decreased risk of being overweight or obese by 4.2% points. CONCLUSIONS: This study provides new population-level, causal evidence that corroborates consistent findings in the epidemiologic literature on the link between short sleep duration and increased body weight.