Everything in Moderation, Including Sleep
Abstract & Commentary
By Barbara A. Phillips, MD, MSPH, Professor of Medicine, University of Kentucky; Director, Sleep Disorders Center, Samaritan Hospital, Lexington. Dr. Phillips reports no financial relationship to this field of study.
Synopsis: Both short (6 or fewer hours) and long (9 or more hours) habitual sleep durations predict an increased risk of weight gain in adults.
Source: Chaput J, et al. The association between sleep duration and weight gain in adults: a 6-year prospective study from the Quebec Family Study. Sleep. 2008;31:517-523.
This paper is a nifty and appropriate exploitation of the Quebec Family Study, which was originally started to understand the genetic basis of obesity and cardiovascular risk. The original study population was 16,150 people from 375 families. The group included in the analysis here was a subset of 276 of those people for whom complete data were available. There were 117 men and 159 women whose mean age was about 39 years. The number of hours of sleep was asked at baseline and again 6 years later by this question in a self-administered questionnaire: "On average, how many hours do you sleep in a day?" The participants were then classified into short sleepers (5-6 hours of sleep), average sleepers (7-8 hours of sleep), and long sleepers (9-10 hours of sleep). Height and weight were carefully measured in the same way both at baseline and at the 6th year. Dietary intake was assessed using food questionnaires, metabolic rate was measured by indirect calorimetry, and physical activity was estimated by a diary. Statistical models adjusted for age, sex, baseline body mass index (BMI), metabolic rate, smoking, alcohol, employment, education, income, menopausal status, shift work, coffee intake, caloric intake, and physical activity.
At enrollment (baseline) the short sleepers were heavier and had higher percentages of body fat and larger abdominal circumferences than the other two groups of sleepers. There were no differences between the short, medium and long sleeper groups for demographics, metabolic rate or total caloric intake. The short-duration sleepers reported more vigorous physical activity than did average-duration sleepers, and were more likely to be shift workers, to smoke, and to drink larger amounts of coffee. In the subsequent 6 years, the short sleepers gained 1.8 kg (about 4 pounds) and the long sleeper 1.5 kg (about 3 ½ pounds) more than the medium sleepers gained. (We are never told how much the medium sleepers gained, but presumably they also gained some weight. However, the short and long sleepers gained more weight than did the medium sleepers). Additionally, short and long-duration sleepers were 35% and 25% more likely to have a 5 kg (about 12 pound) weight gain than the medium sleepers. Further, the short and long-duration sleepers had 27% and 21% increased risk of developing obesity over the 6 year follow-up period than did the average-duration sleepers.
Commentary
This paper reinforces and extends previous work demonstrating a U-shaped relationship between sleep duration and bad outcomes. Several large epidemiologic studies have demonstrated that both long and short sleeper have increased risk of obesity,1 type 2 diabetes2 coronary heart disease,3 and death4 compared with medium-duration sleepers. In most studies, optimum sleep time is between 7 and 8 hours. Most investigators in the area have emphasized the "short end of the stick," and the risks associated with short sleep, while discounting the increased risk to long sleepers. Some investigators have suggested that the increased risk associated with long sleep results from some underlying, uncontrolled-for confounder which is the culprit, rather than the sleep duration itself. For example, perhaps those who sleep longer are more likely to have subtle cardiac disease, which goes undetected and uncontrolled in the analysis, but which ultimately produces a bad outcome. This is certainly a possibility, although evidence of a U-shaped relationship is clearly mounting in multiple extremely well-done studies. In a study of sleep duration and hypertension, Gangwisch reported that short sleep duration was a risk factor for development of hypertension, but the analysis actually demonstrated a U-shaped relationship, with younger individuals "driving" the relationship between short sleep and hypertension, and older people contributing to the relationship between long sleep and hypertension.5
The take home message for our patients may be: everything in moderation, including sleep. There certainly is no evidence that 9 or 10 hours of sleep is better than 7 or 8 (indeed, there's no evidence that 8 is better than 7). Awareness of this U-shaped relationship may be useful in trying to reassure your next middle-aged insomniac that "only" 7 hours of sleep is probably OK.
References
1. Taheri S, et al. Short sleep duration is associated with reduced leptin, elevated ghrelin, and increased body mass index. PLo/s Med. 2004;1:210-217.
2. Cahput JP, et al. Association of sleep duration with type 2 diabetes and impaired glucose tolerance. Diabetologica. 2007;50:2298-2304.
3. Ayas NT, et al. A prospective study of sleep duration and coronary heart disease in women. Arch Intern Med. 2003;163:205-209.
4. Tamakoshi A, Ohno Y, JACC Study Group. Self-reported sleep duration as a predictor of all-cause mortality: results from the JACC study, Japan. Sleep. 2004;27:51-55.
5. Gangwisch JE, et al. Short sleep duration as a risk factor for hypertension. Analyses of the first National Health and Nutrition Examination Survey. Hypertension. 2006;47:833-839.
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