Metabolic consequences of sleep and sleep loss

Abstract

Reduced sleep duration and quality appear to be endemic in modern society. Curtailment of the bedtime period to minimum tolerability is thought to be efficient and harmless by many. It has been known for several decades that sleep is a major modulator of hormonal release, glucose regulation and cardiovascular function. In particular, slow wave sleep (SWS), thought to be the most restorative sleep stage, is associated with decreased heart rate, blood pressure, sympathetic nervous activity and cerebral glucose utilization, compared with wakefulness. During SWS, the anabolic growth hormone is released while the stress hormone cortisol is inhibited. In recent years, laboratory and epidemiologic evidence have converged to indicate that sleep loss may be a novel risk factor for obesity and type 2 diabetes. The increased risk of obesity is possibly linked to the effect of sleep loss on hormones that play a major role in the central control of appetite and energy expenditure, such as leptin and ghrelin. Reduced leptin and increased ghrelin levels correlate with increases in subjective hunger when individuals are sleep restricted rather than well rested. Given the evidence, sleep curtailment appears to be an important, yet modifiable, risk factor for the metabolic syndrome, diabetes and obesity. The marked decrease in average sleep duration in the last 50 years coinciding with the increased prevalence of obesity, together with the observed adverse effects of recurrent partial sleep deprivation on metabolism and hormonal processes, may have important implications for public health.

Fig. 1

Hormonal control of appetite and hunger [18]. NPY; neuropeptide Y; PYY; peptide YY, AgRP: agouti-related protein. Reprinted by permission from Macmillan Publishers Ltd: Nature, Schwartz MW et al. 2002 Aug 8;418(6898):595–7. Copyright © 2002.

Fig. 2

The effect of sleep deprivation on (A) leptin and ghrelin levels and (B) hunger and global appetite ratings[21]. ANNALS OF INTERNAL MEDICINE. ONLINE by Spiegel K, Tasali E, Penev P, Van Cauter E. Copyright © 2004 by American College of Physicians – Journals. Reproduced with permission of American College of Physicians – Journals in the format Journal via Copyright Clearance Center.

Fig. 3

Prevalence of obesity and self-reported sleep in the USA [2]. Reprinted with permission from Medscape Neurology and Neurosurgery 2005. 7(1) http://www.medscape.com/viewarticle/502825 © 2005 Medscape.