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Abstract & Commentary
Synopsis: Sleep restriction (to 4 hours a night) resulted in increased appetite, increased cortisol levels, lowered TSH levels, worsened glucose tolerance and lower heart rate variability compared with sleep extension (to 12 hours a night) in young healthy volunteers.
Source: Speigel K, et al. J Clin Endocrin Metab. 2004;89:5762-5771.
This was a carefully controlled study of 11 healthy nonsmoking unmedicated men whose mean age was 22 years. The study was conducted in a clinical research center, where activity, caloric intake, and environmental factors (such as temperature and light exposure) could be controlled. Subjects were studied in 3 conditions: during six nights with 4 hours in bed (from 01:00 to 05:00), during 7 nights with 12 hours in bed (21:00 to 09:00), and during 3 nights with 8 hours in bed (23:00-07:00). Sleep was polysomnographically recorded, as were body activity, electrocardiographic activity and caloric intake. Blood was sampled at 10 to 30 minute intervals during the last 24 hours of each sleeping condition. Mood and levels of perceived stress were sampled by questionnaires in each condition.
Sleep-efficiency fell from 96% in the 4-hour condition to 76% in the 12-hour condition. Total sleep time for the 3 conditions was 3 hours 49 minutes, 7 hours, 14 minutes, and 9 hours, 3 minutes. Sleep extension (12 hours) resulted in increased amounts of REM and light nonREM sleep. Leptin levels fell markedly during sleep restriction, and the height of leptin secretion occurred earlier. Cortisol levels were higher in the afternoon and evening after sleep restriction than after sleep extension, although 24 hour means were not different. TSH levels were lower with sleep restriction than extension. Post-breakfast HOMA (homeostasis model assessment of glucose tolerance) was elevated (worsened) with sleep restriction. Heart rate variability (a measure of sympathovagal balance) was lower during sleep restriction, indicating either increased sympathetic activity or reduced parasympathetic activity. Scores of self-perceived stress were not different in any of the sleep duration conditions, and were generally low. During the 8-hour sleep condition, values for the variables measured were intermediate between the 4 and 12 hour sleep conditions.
Comment by Barbara A. Phillips, MD, MSPH
This study sheds light on the complex interaction between sleep and metabolic function. Since the first report that sleep deprivation is associated with increased caloric intake,1 investigations into this important link have informed us that sleep duration in young people predicts future weight gain2 and that self-reported sleep duration correlates inversely with BMI.3,4 Leptin is one of several hormones that regulate appetite; increased food intake increases leptin levels, helping to generate satiety and cessation of eating. But even when diet is controlled and continuous (total parenteral nutrition), leptin levels are elevated during sleep compared with waking, indicating that sleep, in and of itself, affects leptin regulation. The relationship between eating and sleeping appears to be circular: in rats, sleep deprivation is associated with overeating,5 but starvation is associated with decreased sleep.6
Clinically, there are a couple of implications of this work. The first is that people who are trying to lose weight (this seems to be just about everybody these days) need to know that sleep is important in appetite regulation; sleep loss really does make you feel hungrier. Another implication is a partial explanation of why folks with sleep apnea seem to be in a vicious, nearly unbreakable cycle of weight gain. It is likely that their fragmented sleep contributes to this inexorable weight gain. More and more, I am seeing bright motivated people with sleep apnea who just cannot lose the weight no matter how hard they try. Early reports do not support the notion that sleep apnea treatment helps with weight loss, but it is likely that longer term studies will.
Dr. Phillips, Professor of Medicine, University of Kentucky; Director, Sleep Disorders Center, Samaritan Hospital, Lexington, KY, is Associate Editor of Internal Medicine Alert.
1. Spiegel K, et al. Lancet. 1999;354:1435-1439.
2. Hasler G, et al. Sleep. 2004;27:661-666.
3. Kripke DR, et al. Arch Gen Psychiatry. 2002;59: 131-136.
4. Vioque J, et al. Int J Obes Relat Metal Disord. 2000;24:1683-1688.
5. Rechtschaffen A, et al. Science. 1983;221:183-184.
6. Danguir J, Nicolaidis S. Physiol Behav. 1979;22: 735-740.