The Obesity-Sleep Deprivation Connection
Catherine Darley, ND
Over the last several decades the incidence of obesity in the U.S., and indeed the world, has increased profoundly. Adult overweight is defined as a body mass index (BMI) above 25kg/m2, while obesity is defined as BMI ≥ 30kg/m2 (National Heart, Lung and Blood Institute, n.d.). Children are considered overweight if they are above the 95th percentile on the growth chart for their age and sex. In 1999, 27% of American adults were obese on self-report. This has grown significantly from the 13.3% reported in 1960 (U.S. Dept. of Health and Human Services, 2002). For example, a woman who is 5’4” tall is considered overweight at 150 pounds and obese at more than 180 pounds. A 5’10” man is considered overweight at more than 180 pounds and obese at more than 210 pounds. The increased incidence of obesity has been characterized as an epidemic by the medical community.
Health Problems of Obesity
Obesity is associated with many health problems. Among obese people, the incidence of high cholesterol, hypertension and elevated fasting blood sugar is significantly higher than in lean people. Along with a higher incidence of these diseases, there are higher mortality rates from coronary heart disease and cardiovascular disease (Tsai, 2006). Recent research has pointed to sleep deprivation as a contributing factor in the increased incidence of obesity.
The Sleep Deprivation “Epidemic”
As obesity rates have increased, the average number of sleep hours per night have decreased. As early as 1995, Bonnet and Arand in their paper, We Are Chronically Sleep Deprived, stated that “common sleep lengths of ≤ 6.5 hours can be disastrous.” From 2001 to 2005, the mean hours of sleep on weekday nights decreased from 7.0 to 6.8 hours, and a full 16% reported getting less than six hours each weeknight (2005 Sleep in America Poll).
Many Americans are considered to be partially sleep deprived. Chronic partial sleep deprivation is not strictly defined, but some authors have defined it as getting one hour less sleep per night than is needed by the individual. A full 22% of Americans report getting less sleep than they think they need on weeknights (2005 Sleep in America Poll).
The International Classification of Sleep Disorders, Diagnostic and Coding Manual includes behaviorally induced insufficient sleep syndrome. The diagnostic criteria are:
- Complaint of excessive sleepiness for at least three months
- Habitual sleep time is shorter than expected
- Patients will sleep longer on weekends or vacations
- Overnight polysomnography shows sleep efficiency >90%
- Hypersomnia is not explained by another disorder.
This is coded in ICD-9 as 307.44 (American Academy of Sleep Medicine, 2005).
Sleep Deprivation Contributes to Obesity
Research has been done on the direct relationship between sleep deprivation and obesity. Gangwisch et al. found that among people aged 32 to 49, those who slept seven hours were the most likely to have a BMI <25. As the hours of sleep per night decreased from seven, participants’ BMI increased (see Figure 1). Those people who reported getting only two to four hours of sleep had a 235% higher likelihood of being obese than those who slept seven hours a night. In this study, there was neither an increased nor decreased probability of obesity among those people who got more than seven hours of sleep each night (Gangwisch, 2005).
These two epidemics are linked in that sleep deprivation alters the hormones related to appetite and metabolism. Primary among the appetite hormones are leptin and ghrelin. Other hormones that may influence weight and are altered by sleep deprivation include TSH and cortisol.
Sleep-deprived individuals may also find it more difficult to maintain the motivation to exercise and eat healthily, which is another way sleep deprivation can contribute to obesity.
- Leptin Leptin is a hormone secreted by adipocytes, which signals to the brain that sufficient calories have been ingested. Ingesting a meal increases leptin levels and decreases appetite. Sleep, regardless of the time of day one sleeps, raises leptin levels (Simon, 1998). Studies of the impact of sleep deprivation on leptin levels kept caloric intake and activity levels constant while participants underwent partial sleep deprivation (four hours per night), control sleep (eight hours per night) and sleep extension (12 hours per night) for six days. The purpose of studying sleep extension is to ensure that participants have been able to get all the sleep they need. Mean levels of leptin were decreased by 19% in the partial sleep restriction compared to when participants were fully rested (Spiegel, 2004).
- Ghrelin Ghrelin plays an opposite role by stimulating appetite. It is produced by the stomach. During partial sleep restriction to four hours in bed per night, ghrelin levels increased by 28% (Spiegel, 2004). In this study, researchers also evaluated appetite and hunger by asking participants to rate each on visual analog scales. During the study their caloric intake was kept constant by giving them IV glucose rather than meals. Compared to their hunger during sleep extension, they were 24% more hungry during sleep restriction. Interestingly, their appetite for various foods also changed. Their appetite for calorie-dense, high-carbohydrate foods such as sweets, salty and starch foods was increased by 12%, while their appetite for fruits and vegetables increased by only 4% (see Figure 2). These changes can contribute to obesity.
- Cortisol Researchers have looked at how partial sleep deprivation impacts other hormonal axes. Cortisol, a glucocorticoid, is normally lowest at night and highest in the early morning. However, when people are either totally or partially sleep deprived, their evening cortisol is significantly increased, and the nadir is delayed by at least one hour (Leproult, 1997). High cortisol will produce hyperglycemia, which in turn can contribute to cardiovascular disease.
- TSH Spiegel et al. (2004) found that mean 24-hour TSH was 26% lower when sleep was restricted to just four hours. Another study assessed the relationship between leptin and TSH in women; it was found that 24-hour TSH levels were positively correlated with leptin levels. Leptin is thought to stimulate the secretion of TSH, thus making sense of Spiegel’s finding, as sleep restriction results in lower leptin levels.
Sleep Deprivation and Cardiovascular Health
Not only are hormones altered by partial sleep deprivation, but so too are inflammatory mediators. In one study, after ten days of partial sleep deprivation (four hours per night), C-reactive protein (CRP) concentrations increased (Meier-Ewert, 2004).
In the study described earlier in which participants were first sleep restricted and then sleep extended, another marker for cardiovascular risk was elevated. In this study, heart rate variability was measured. The morning rise in cardiac sympathovagal balance was significantly increased during sleep restriction, which can adversely affect the cardiovascular system (Spiegel, 2004).
Another study evaluated proinflammatory cytokines after one week of restricting sleep to six hours, a sleep schedule that easily replicates what many people voluntarily do. The study measured 24-hour secretion, showing that IL-6 was elevated in both men and women, and TNF-a was elevated in men (Vgontzas, 2004). Inflammation can contribute to cardiovascular disease.
Over the last decade, medical research has begun to establish the link between chronic partial sleep deprivation and obesity. Sadly, it is true that a meaningful percentage of Americans are chronically sleep deprived. Even partial sleep deprivation changes the body’s functioning by decreasing leptin, increasing ghrelin and thereby increasing appetite and contributing to obesity. Sleep deprivation also contributes more directly to cardiovascular disease by increasing CRP levels and the levels of proinflammatory cytokines.
As NDs, one of our principles is to establish wellness. Sleep health is as basic to establishing wellness as are a healthy diet and adequate exercise. There are many other ways adequate sleep supports health that were not discussed in this article. At the least, reviewing patients’ sleep habits to ensure they are adequate will reduce their risk of obesity, which is important to address in the face of the epidemic of obesity and the associated risks to cardiovascular health.
Catherine Darley, ND a graduate of Bastyr University, practices at The Institute of Naturopathic Sleep Medicine in Seattle. Dr. Darley is passionate about the role healthy sleep plays in overall health and quality of life, and is pioneering the field of naturopathic sleep medicine. She gained her expertise by working in the field of sleep research and medicine through naturopathic medical school and doing multiple preceptorships and post-graduate courses with sleep specialists. In addition to providing patient care, she works to educate the public about sleep health.
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