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Abstract & Commentary
Synopsis: Young people who sleep less are more likely to be and to become obese.
Source: Hasler G, et al. Sleep. 2004;27:661-666.
This was a prospective, interview-based study of people from the Zurich Cohort Study, a group of individuals selected to be at risk for psychiatric disorders.1 All participants underwent screening with a sociodemographic questionnaire and the Symptom Checklist 90-R (SCL-90-R), which is a psychological symptoms questionnaire.2 Initially, 292 men and 299 women were enrolled. They underwent the Structured Psychopathological Interview and Rating of the Social Consequences for Epidemiology (SPIKE) interview,1 measurement of Body Mass Index (BMI), and questions about sleep duration and quality at the ages of 27, 29, 34, and 40. Of the 591 who started the study, only 367 were followed until age 40. Short sleep was defined as less than 6 hours a night.3 Data were analyzed in several ways, including by gender, for SCL-90-R high and low scorers, and by sociodemographic variables. Associations between sleep duration and obesity were analyzed both using BMI as a continuous variable and using BMI as a dichotomous (yes/no for obesity) variable.
On average, women slept more than men at all ages (eg, 7.7 hrs vs 7.13 hrs at age 27), and sleep duration declined with age (eg, 7.13 hours at age 27 and 6.9 hours at age 40 for men). Those of low socioeconomic status slept less than those of higher socioeconomic status. Scores on the SCL-90-R did not correlate with sleep duration. Thus, analyses were controlled for gender, age, and socioeconomic status, but not for SCL-90-R score.
At ages 27, 29, and 34, those who reported sleeping less than 6 hours were more likely to be obese at those ages, and at previous and future ages, up until the age of 40. For example, a person who slept less than 6 hours at the age of 29 had odd ratios for obesity of 8.1 (CI, 1.8-37.4), 4.6 (CI, 1.3-16.5), and 11.8 (1.6-86.5) at ages 29, 34, and 27, respectively. There was a linear inverse relationship between sleep duration and BMI. Impaired sleep quality, insomnia, awakenings during sleep, and daytime sleepiness were not associated with obesity. The relationship between sleep and obesity was not significant at the age of 40.
Comment by Barbara A. Phillips, MD, MSPH
Obesity is quickly overtaking smoking as the most prevalent preventable cause of death in the United States. As more interest focuses on weight loss, we are queried daily about the relative utility of the Atkins diet, the South Beach diet, gastric reduction surgery, etc, etc. Our patients are desperately looking for weight loss plans that do not involve consuming fewer calories or burning more of them. Perhaps we should tell them about the relationship between sleep, weight, and appetite. This is a new story, and much is still unclear, but 2 important themes are emerging: 1. sleep has something to do with metabolism and appetite regulation; 2. our bodies have a U-shaped relationship with sleep, just as they do with calories: both too much and too little are bad for you.
Sleep duration has consistently been shown to have a U-shaped relationship with morbidity and mortality, with the lowest risk being seen for those sleeping 7 or 8 hours a night, and increasing risk for either ends of the U. For example, Ayas showed that women sleeping fewer than 6 or more than 9 hours of sleep a night were at increased risk of coronary events4 and mortality,5 essentially confirming earlier work by Kripke.6
In cross-sectional studies of sleep duration and metabolic problems, investigators have chosen to focus on the short sleep end of the U. And there is plenty of circumstantial evidence that short sleep is associated with obesity. Take the 2 sleep-deprived groups of college freshmen (with their freshman 15) and medical interns, for example. In fact, the increase in obesity in this country has paralleled a decrease in the average amount of nightly sleep obtained by Americans. Ayas previously showed an association between short sleep and diabetes,3 and von Kries demonstrated that prevalence of obesity decreases by duration of sleep even in young children, controlling for other risk factors.7
Biologically, it’s important to remember that circadian rhythm and metabolic function are closely related. Things that disturb sleep also disturb circadian rhythm, which in turn disturbs metabolic function. Sleep-deprived normal people have increased cortisol levels, worsened glucose tolerance, reduced leptin levels (appetite suppressant hormone) and increased caloric intake compared with when they are rested.8,9
The current study by Hasler and colleagues is important because it is prospective, includes a well-defined cohort, and strictly controls for most known confounders. It also shows a "dose response" relationship between BMI and sleep duration, although the dose-response curve is fairly flat between 5 and 9 hours of sleep. The relationship between sleep and weight weakened at the age of 40, which suggests that what we do in early life builds a foundation for further health. Although you may feel like saying "duh" at this point, maybe we should be advising our patients that getting enough sleep is important for current and future health, including affecting their risk of obesity in mid-life.
But before you tell your patients to go on the Rip van Winkle Diet, remember that, at least for cardiovascular disease and for all-cause mortality, too much sleep is as bad as too little.4-6 Moderation in everything, including sleep. The magic number is 7 hours.
Dr. Phillips,, Professor of Medicine, University of Kentucky; Director, Sleep Disorders Center, Samaritan Hospital, Lexington, KY, is Associate Editor of Internal Medicine Alert.
1. Angst J, et al. Eur Arch Psychiatry Clin Neurosci. 1984;234:13-20.
2. Derogatis LR. Administration, Scoring and Procedures Manual-I for the R (revised) version and Other Instruments of the Psychopathology Rating Scale Series. Baltimore, Md: Johns Hopkins School of Medicine. 1997.
3. Ayas NT, et al. Diabetes Care. 2003;26:380-384.
4. Ayas NT, et al. Arch Intern Med. 2003;163:205-209.
5. Patel SR, et al. Sleep. 2004;27:440-444.
6. Kripke DF, et al. Arch Gen Psychiatry. 2002;59: 131-136.
7. von Kries R, et al. Int J Obes Relat Metab Disord. 2002;26(5):710-716.
8. Spiegel K, et al. Lancet. 1999;354:1435-1439.
9. Spiegel K, et al. Sleep. 2003;26:A174.