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.
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 p.m. 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 to 12th grades surveyed in the 2009−2012 Korea Youth Risk Behavior Web-based Survey.
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/m2 reduction in body mass index (95% confidence interval: 0.07 to 1.05) and a decreased risk of being overweight or obese by 4.2% points.
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.
1Department of Health Policy and Management, Seoul National University College of Medicine, Seoul, Korea
2Institute of Health Policy and Management, Seoul National University Medical Research Center, Seoul, Korea
Conflict of Interests: The author has declared that there is no conflict of interest.
Source of financial support: This work was supported by Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Science, ICT & Future Planning [NRF-2014R1A1A1004945]. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Acknowledgments: This study used data from the Korea Youth Risk Behavior Web-based Survey, administered by the Ministry of Education, Science and Technology, Ministry of Health and Welfare, and Korea Centers for Disease Control and Prevention. An earlier version of this paper was published as a Stanford Asia Health Policy Working Paper. I thank Mary Ann Bautista, Ada Batcagan-Abueg, Eunhae Shin, and Sungchan Kang for helpful assistance. I also thank Marcel Bilger, Soo-yong Byun, Sukyung Chung, Eric Finkelstein, Hai V. Nguyen, Bisakha Sen, and Justin White for useful comments on earlier versions of this paper. I appreciate discussions with Young-Ho Khang. This paper has benefited from comments of conference and seminar participants at the American Society of Health Economists Biennial Conference, International Association for Time Use Research Conference, World Congress of Sleep Medicine, Duke-NUS Medical School Singapore, Hallym University Graduate School of Public Health, Korean Institute of Health and Social Affairs, Max Planck Institute for Demographic Research, Max Planck Institute for Human Development, Seoul National University Graduate School of Public Health, Seoul National University Program in History and Philosophy of Science, Sogang University School of Economics, and Yonsei University. I am grateful to two anonymous reviewers for helpful suggestions. All errors are my own.
Corresponding author: Young Kyung Do, M.D., M.P.H., Ph.D. Professor, Department of Health Policy and Management, Seoul National University College of Medicine, 103 Daehak-ro, Jongno-gu, Seoul 03080, Republic of Korea, E-mail: email@example.com
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