Picture of Emily Sleeping on Pillow thanks to Eric Rolph.
Our sleeping and eating routines are intricately woven. Take an animal's food away (whether forcibly or in the case of an eating disorder, voluntarily) and they sleep less.1, 2 Take an animal's sleep away and they eat more, lots more - and the food they choose is calorie-dense and high in carbohydrates.3, 4
This relationship between lack of sleep and food intake isn't just a byproduct of being awake more and having more opportunities to surrender to the temptation of that chocolate cake in the fridge. The relationship is hard-wired - controlled by neurons, hormones, and other mediators, and thought to have evolved to protect against starvation during times of famine. If you're starving, best to continue foraging than sleeping. And if you haven't been sleeping, it must be because you're starving - Eat!
During sleep, the body releases more leptin (a hormone that suppresses appetite). When sleep is restricted, the body releases more ghrelin (a hormone that stimulates appetite). Slice a few hours off nighttime sleep and the combination of these hormonal influences on hunger will be profound - and animals are compelled to satisfy that hunger at the expense of their girth. Progressive increases in body weight and BMI (Body Mass Index) have been measured in people who regularly sleep less that 8 hours each night.5, 6, 7
Above you see sleep durations during the last 50 years.8 Self-reported sleep durations fell by up to 2 hours in the last half century, from an average of 8.5 hours in 1960, to 6.8 hours today.9 This downward trend in sleep mirrors an upward trend in body weight. Twenty years ago, 47% of Americans were either overweight or obese; by 2002 that number rose to 65%.10
On a related note, sleep restriction has also been shown to increase insulin resistance and impair glucose tolerance, increasing the risk for type 2 diabetes. The mechanism is both direct, through alterations in levels of glucose-controlling hormones, and indirect, through increase in body weight brought about by the process described above. In fact, when a group of young healthy men's nighttime sleep was restricted to 4 hours, it took them 40% longer to clear an injection of glucose than when their sleep was not restricted.11
Getting more sleep is one change I doubt multitasking will help to incorporate, no matter how many people I see trying to catch some zzz's on the treadmill.
1 Lauer CJ, Krieg JC. Sleep in eating disorders. Sleep Med Rev: 2004, 8(2); 109-118.
2 Danguir J, Nicolaidis S. Dependence of sleep on nutrients' availability. Physiol Behav: 1979,22(4); 735-740.
3 Bhanot JL, Chhina GS, Singh B, Sachdeva U, Kumar VM. REM sleep deprivation and food intake. Indian J Physiol Pharmacol: 1989, 33(3): 139-145.
4 Everson CA, Bergmann BM, Rechtschaffen A. Sleep deprivation in the rat: III. Total sleep deprivation. Sleep: 1989, 12(1);13-21.
5 Spiegel K, Tasali E, Penev P, Van Cauter E. Brief communication: Sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite. Ann Intern Med: 2004, 141(11);846-850.
6 Spiegel K, Leproult R, L'hermite-Baleriaux M, Copinschi G, Penev PD, Van Cauter E. Leptin levels are dependent on sleep duration: relationships with sympathovagal balance, carbohydrate regulation, cortisol, and thyrotropin. J Clin Endocrinol Metab: 2004,89(11);5762-5771.
7 Taheri S, Lin L, Austin D, Young T, Mignot E. Short sleep duration is associated with reduced leptin, elevated ghrelin, and increased body mass index. PLoS Med: 2004, 1(3); e62.
8 Van Cauter E , Knutson K, Leproult R, Spiegel K. The impact of sleep deprivation on hormones and metabolism. Medscape Neurology & Neurosurgery: 2005, 7 (1).
9 National Sleep Foundation
10 CDC: National Center for Health Statistics. Prevalence of overweight and obesity among adults: United States, 1999-2002.
11 Spiegel K, Leproult R, Van Cauter E. Impact of sleep debt on metabolic and endocrine function. Lancet: 1999, 354(9188);1435-1439.