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Until relatively recently, common clinical wisdom held that the state of sleep was largely a period of quiescence, with the body simply resting to conserve energy for accomplishing waking tasks. It was also thought that the purpose of sleep had largely to do with bodily functions centered in the brain and nervous system. Discovery of REM sleep in the early 1950’s was a first clue to dispelling the notion of inactivity. And while the second idea has some truth, since sleep disruption causes dysfunction of emotion regulation and cognition, recent discoveries have led to the realization that many physiological systems are affected by sleep patterns. Regulation of body weight involves multiple body systems, including the digestive, musculoskeletal, and endocrine systems. Evidence is accumulating that strongly implicates a role for sleep in weight gain for adults, adolescents, and children.
Considerable evidence suggests that sleep times for adults and children have become shorter over the past decades, and there have been corresponding increases in body weight. As the U.S. map indicates, rates of overweight and obesity among children is between 25% and 45% in 47 of 50 states (http://healthyamericans.org/reports/obesity2009/). Effects of obesity are wide ranging and devastating. Besides short and long range health risks, overweight and obese children are subject to more bullying that results in psychological harm (Gray et al. 2009) and lower school achievement (Taras & Potts-Datema, 2005)
When researchers have studied many groups of individuals, the relationships between sleep and obesity have been striking. In 2008, Cappuccio and colleagues published a meta-analysis of studies conducted over the last decade and reported a pooled odds ratio of 1.86 for a dozen studies done with children. Simply stated, a child who sleeps shorter periods is 1.86 times more likely to be obese. More recently, researchers have looked at dimensions of sleep other than duration. In a study reported last month in the International Journal of Obesity, Jarrin, McGrath, & Drake (2013) found obesity in children related to measures of sleep quality, sleep disturbance, and delayed sleep phase (going to sleep later in the evening).
Many studies of this relationship are based on epidemiological and correlational studies. There are plausible reasons that poor sleep leads to obesity, and some possible ways that obesity may lead to poor sleep. Randomized clinical trials with volunteers agreeing to limit their sleep provide definitive ways to determine directions of effects, and they also provide opportunities to understand underlying mechanisms. These kinds of studies are rare in children, since ethical constraints prohibit intentionally depriving children of sleep, but recent discoveries with adults have been striking. In a study of healthy young adults, Broussard et al. (2012) restricted sleep to 4.5 hours of time in bed vs. 8.5 hours over a period of four days. Caloric intake and physical activity were closely monitored and controlled. Analyses of adipose (fat) cells biopsied from the abdomen showed that sleep restriction resulted in less cellular insulin sensitivity, a condition associated with both obesity and diabetes. This study and others are showing how sleep is involved in physiological regulation at the cellular level.
If children are overweight and obese, their school performance, emotional adjustment, and physical health are put at risk. We are beginning to understand not only that poor sleep is involved in these relations, but new evidence also suggests how these relations develop.
Broussard, J.L., Ehrmann, D.A., Van Cauter, E., Tasali, E., & Brady, M.J. (2012). Impaired insulin signaling in human adipocytes after experimental sleep restriction: A randomized, crossover study. Annals of Internal Medicine, 157, 549-557.
Cappuccio, F.P., Taggart, F.M., Kandala, N.B., Currie, A., Peile, E., Stranges, S., & Miller, M.A. (2008). Meta-analysis of short sleep duration and obesity in children and adults. Sleep, 31, 619–626.
Gray, W.N., Kahhan, N.A., & Janicke, D.M. (2009). Peer victimization and pediatric obesity: A review of the literature. Psychology in the Schools, 46, 720-727.
Jarrin, D.C. McGrath, J.L. & Drake, C.L. (2013). Beyond sleep duration: Distinct sleep dimensions are associated with obesity in children and adolescents. International Journal of Obesity. Published online19 February 2013. doi:10.1038/ijo.2013.4
Taras, H. & Potts-Datema, W. (2005). Obesity and student performance at school. Journal of School Health, 75, 291-295.
