Sleep Facts: The Italian Renaissance artist and inventor, Leonardo da Vinci, who painted the Mona Lisa, would sleep 15 minutes out of every 4 hours—a daily total of 1 1/2 hours of sleep.
“After two nights of 4 hours of sleep, the volunteers found foods such as candy, cookies and cake far more appealing. The sleep-deprived subjects’ desire for high-carbohydrate, calorie-dense foods increased by a whopping 45 percent.”
Eating healthy and regular exercise are critical components for weight control, but there may be an additional component that is missing, which just happens to be a critical component of weight control—a good night’s sleep! If you are not sleeping at least 7 to 8 hours a night, you may be putting yourself at risk for future weight gain. In the largest sleep study to date, a survey on sleep duration in over 1 million participants concluded that increasing weight gain occurred for participants sleeping less than 7 to 8 hours a night.2 Women who get a good night’s sleep are less likely to gain weight as compared to those who are sleep deprived.1 In a study where 68,183 women’s bodyweight and habitual sleep length were tracked over a 16-year period, it was found that those participants who were sleeping 5 hours or less each night gained more weight than those who slept 7 hours or more. The overall conclusion was women who slept at least 7 to 8 hours a night had the lowest risk of gaining weight in the future. Americans are sleeping less each night than ever before. However, this lack of sleep may help explain why so many chronically sleep-deprived Americans also are overweight.
A Sleep Deprived Country
In our fast-paced society, sleep is the one aspect of our life that is always neglected. Staying up late to work, play, read, socialize or watch television all can be detrimental to health and fitness. Humans are the only mammals to voluntarily ignore their sleep needs. In the last 40 years, American adults have cut their average sleep time by nearly 2 hours. In 1960, U.S. adults slept an average of 8.5 hours a night. By 2002, that had fallen to less than 7 hours a night. Over the same period, the proportion of young adults sleeping less than 7 hours increased from just over 15 percent to 37 percent. Now, only 24 percent—or less than one out of four young adults—sleep at least 8 hours a night.5 The reason why inadequate sleep may lead to future weight gain is because sleep loss can increase hunger, which stimulates hormones and reduces key fat-burning hormones.13
Sleep Loss Leads to Increased Appetite
Sleep loss could be part of the reason sleepy college students, new parents and shift workers experience weight gain. Work, family and social requirements all make demands of our time, allowing less and less time for sleep. Data from the National Health and Nutrition Examination Survey (NHANES) showed that individuals aged 32 through 49 with sleep durations of less than 7 hours a night weighed more than those who slept greater than 7 hours per night.14
Another study found that obese patients sleep significantly less than normal-weight patients.16 Although the mechanisms linking inadequate sleep and obesity are unknown, there is evidence to suggest sleep deprivation can lead to alterations in appetite regulation in healthy subjects. To investigate how sleep loss affects short-term appetite control, researchers had subjects come into a hospital laboratory to sleep and eat breakfast and dinner. On one occasion, they were limited to 4 hours of sleep for two consecutive nights. At another time, they were allowed up to 10 hours of sleep for two nights. The findings of the study showed that people who had only 4 hours of sleep experienced altered circulating levels of the two hormones that regulate hunger: leptin and ghrelin. Ultimately, this caused an increase in their appetite and their desire for calorie-dense, high-carbohydrate foods. Research subjects who slept only 4 hours a night for two nights had an 18 percent decrease in leptin, the hormone that tells the brain there is no need for more food. Plus, there was a 28 percent increase in ghrelin, a hormone that triggers hunger. As hunger increased, their food preferences changed. After two nights of 4 hours of sleep, the volunteers found foods such as candy, cookies and cake far more appealing. The sleep-deprived subjects’ desire for high-carbohydrate, calorie-dense foods increased by a whopping 45 percent. Talk about a case of the munchies!
In humans, circulating leptin and ghrelin hormones are altered when dieting and weight loss occurs. Both hormones signal appetite regulation centers in the brain. Not getting enough sleep makes your body think there is a food shortage and activates the appetite centers in the brain. For example, in one study, after three months of dietary supervision, a reduction in BMI of approximately 5 percent was associated with a 12 percent increase in ghrelin and a 15 percent decrease in leptin.17 These changes in ghrelin and leptin—which increase appetite—are comparable to those observed with sleep loss of 2 to 3 hours per night. Both hormones are believed to be active in energy regulation. In the Wisconsin Sleep Study, subjects were surveyed on how many hours of sleep they got at night and had morning blood samples drawn. Those classified as short sleepers (less than 5 hours) were associated with 16 percent lower leptin levels and 15 percent higher ghrelin levels compared to those who slept 8 hours a night.15 Would our lives be so much easier if we had the sleep cycle of giraffes? The giraffe has one of the shortest sleep requirements of any mammal, which is between 10 minutes and 2 hours in a 24-hour period. We apparently spend one-third of our lives doing nothing (sleeping). But is sleep really doing nothing? It looks like it; our eyes are closed, our muscles are relaxed, our breathing is regular—and we do not respond to sound or light. If you take a look at what is happening inside your body, hormones are being activated that regulate metabolism and burn fat.
Here is a short list of the major hormones affected by sleep loss:
- Cortisol has been termed “the stress hormone” because it’s also secreted in higher levels during the body’s response to stress. Human studies have shown cortisol injections are associated with increased appetite, cravings for sugar, and weight gain. Women who don’t handle stress well also secrete more cortisol during and after stress and choose to eat more foods high in sugar and fat.8 Cortisol has set rhythms in the body. Normally, it’s present in the body at higher levels in the morning, and at it’s lowest at night. Sleep loss or disruption throws off the body’s normal cycle. So after a night of not enough sleep, cortisol levels are elevated the entire next day. The rate of decrease of cortisol concentrations in the early evening was approximately six times slower in subjects who had undergone six days of sleep restriction than in those who were fully rested7. Elevations of evening cortisol levels in chronic sleep loss are likely to promote the development of insulin resistance, a risk factor for obesity and diabetes.
- Leptin (from the Greek leptos, meaning thin) is a protein hormone with important effects in regulating bodyweight and metabolism. Leptin suppresses appetite and increases metabolic rate, and is thought to play a role in long-term regulation of bodyweight. Leptin is produced by fat cells and tells the brain when the body does or doesn’t need more food. During sleep, leptin levels normally rise, but levels are also dependent on sleep duration. The nighttime rise of leptin is partly a response to why we wake up hungry. Sleep loss results in lower leptin levels which basically says to the brain: “I am hungry!” After six days of 4 hours of sleep per night, the plasma concentration of leptin was decreased by 26 percent compared to those who were adequately rested.9 The low level of leptin caused by inadequate sleep has been associated with obesity.
- Ghrelin is a hormone produced largely in the stomach that is involved in the regulation of appetite. Ghrelin accelerates appetite. In humans, ghrelin increases hunger through its action on the brain’s feeding centers. Humans injected with ghrelin report sensations of intense hunger; in one study, when turned loose at a buffet, those injected with ghrelin ate 30 percent more food than they would normally.10 Sleep loss has been shown to elevate ghrelin levels during the day, which makes you hungrier.
- Growth Hormone (GH) increases fat metabolism, diminishes fat storage and increases lean muscle. GH secretion follows a circadian rhythm and is released in small surges or pulses of six to 12 per day, with the largest pulse secreted about 1 or 2 hours after the onset of deep sleep.2 If we don’t get enough sleep, we end up sabotaging our body’s capacity to burn fat and renew tissues. For example, researchers studied healthy subjects on two occasions. On one occasion, they suppressed nighttime GH release and compared it to another occasion when they had a normal night’s sleep. Without the normal nighttime rise in plasma GH concentration, this led to a reduction in fat mobilization from the stomach on the following day.18
Sleep plays an essential role, not only for proper development and maintenance of the brain, but also for the entire body. Sleep loss in addition to weight gain is associated with a shortened life span, high blood pressure, diabetes and heart disease. Training individuals, especially those engaging in high-intensity workouts, can have up to three times the amount of deep sleep, (representing 25 percent to 35 percent of the night’s sleep) since a deep slumber is needed for muscle recuperation. It seems that not getting a good night’s sleep results in an increase in appetite and an overconsumption of calories the next day, which could result in an increase in weight over time. It could also be that reduced sleep leads to daytime fatigue and therefore reduces physical activity. Although weight gain is a multifactorial process involving changes in metabolism, some researchers believe when we sleep more, we simply have less time in which to eat.11 Getting sleep may be just as important as eating healthy and exercising to control weight. It’s imporatant to get at least 7 to 9 hours of sleep, depending on your need for sleep. It should also be noted that in the survey, on inadeqaute sleep as a risk factor for obesity, it was found that every additonal hour of sleep after 7 hours was associated with a reduced likelihood of future weight gain.14 Who ever thought that something as simple as sleeping more could help beat the battle of the bulge?
- Patel SR, Malhotra A, White DP, Gottlieb DJ, Hu FB. Association between reduced sleep and weight gain in women. Am J Epidemiol, 2006 Nov 15;164(10):947-54.
- Chussler P, Uhr M, Ising M, Weikel JC, Schmid DA, Held K, Mathias S, Steiger A. Nocturnal ghrelin, ACTH, GH and cortisol secretion after sleep deprivation in humans. Psychoneuroendocrinology, 2006 Sep;31(8):915-23
- Kripke DF, Garfinkel L, Wingard DL, Klauber MR, Marler MR. Mortality associated with sleep duration and insomnia. Arch Gen Psychiatry, 2002 Feb;59(2):131-6.
- Young T, Palta M, Dempsey J, Skatrud J, Weber S, Badr S. The occurrence of sleep-disordered breathing among middle-aged adults. N Engl J Med, 1993 Apr 29;328(17):1230-5.
- National Sleep Foundation. 2005 “Sleep in America” poll. Washington, DC: National Sleep Foundation; 2005.
- Leproult R, Copinschi G, Buxton O, Van Cauter E. Sleep loss results in an elevation of cortisol levels the next evening. Sleep, 1997 Oct;20(10):865-70.
- Spiegel K, Leproult R, Van Cauter E. Impact of sleep debt on metabolic and endocrine function. Lancet, 1999;354:1435-1439.
- Epel, E., R. Lapidus, B. McEwen, et al. Stress may add bite to appetite in women: a laboratory study of stress-induced cortisol and eating behavior. Psychoneuroendocrinology, 26: 37-49, 2001.
- 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 Nov;89(11):5762-71.
- Schmid DA, Held K, Ising M, Uhr M, Weikel JC, Steiger A. Ghrelin stimulates appetite, imagination of food, GH, ACTH, and cortisol, but does not affect leptin in normal controls. Neuropsychopharmacology, 2005 Jun;30(6):1187-92.
- Astrup A. Have we been barking up the wrong tree: can a good night’s sleep make us slimmer? Int J Obes (Lond). 2006 Jul;30(7):1025-6.
- Prinz P. Sleep, appetite, and obesity–what is the link? PLoS Med, 2004 Dec;1(3):e61. Review.
- Gangwisch JE, Malaspina D, Boden-Albala B, Heymsfield SB. Inadequate sleep as a risk factor for obesity: analyses of the NHANES I. Sleep, 2005 Oct 1;28(10):1289-96.
- 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 Dec;1(3):e62.
- Vorona RD, Winn MP, Babineau TW, et al. Overweight and obese patients in a primary care population report less sleep than patients with a normal body mass index. Arch Intern Med, 2005;165:25-30.
- Hansen TK, Dall R, Hosoda H, Kojima M, Kangawa K, et al. (2002) Weight loss increases circulating levels of ghrelin in human obesity. Clin Endocrinol, (Oxf) 56:203–206.
- Samra JS, Clark ML, Humphreys SM, MacDonald IA, Bannister PA, Matthews DR, Frayn KN. Suppression of the nocturnal rise in growth hormone reduces subsequent lipolysis in subcutaneous adipose tissue. Eur J Clin Invest, 1999 Dec;29(12):1045-52.