Inadequate sleep is an important risk factor for obesity. A literature review of 71 studies by Danish researchers concluded that short sleep duration was linked to obesity in children and young adults, but the evidence was less clear in older adults. Several studies compared energy balance in subjects who slept normally with others deprived of sleep. The sleep-deprived groups gained weight.
Sleep loss causes an increased release of the hormone ghrelin, which boosts appetite and slows metabolic rate. The resulting fatigue makes it more difficult to follow a healthy lifestyle that includes exercise. Poor sleep habits could be contributing to the obesity epidemic. Many factors cause sleep deprivation, so it is difficult to make generalizations based on large population studies. (Obesity Reviews, 12: 78-92, 2011)