Obesity has reached epidemic proportions in the past two decades in both children and adults. Over the past 25 years, obesity rates have doubled in adults and tripled in children. Almost 300,000 deaths per year are attributable to obesity, and the costs of treating obesity-related health problems constitute about 10% of health care costs. Although most of the attention concerning the obesity epidemic has focused on diet and exercise, emerging research suggests that we may have underestimated another lifestyle variable that may impact obesity: sleep.
At the same time that obesity rates have increased, the prevalence of insomnia and sleep deprivation have also increased. In a recent issue of the journal Sleep, researchers studied a sample of 500 people over a 13 year period. They found a relationship between increased body weight and decreased sleep time and showed that sleep restriction was associated with future weight gain. These findings are consistent with prior findings demonstrating that chronically reduced sleep durations are associated with obesity. Although these findings suggest that sleep deprivation may play a casual role in the development of obesity, the study was not able to show such a cause-and-effect relationship. Although the relationship between sleep loss and obesity may be explained by the fact that recent studies have shown that sleep deprivation reduces levels of leptin, a satiety hormone that diminishes appetite, it is also possible that sleep apnea, an underling sleep disorder that involves disturbed breathing during sleep, may also increase obesity through disturbance of sleep.
In a recent study in the Annals of Internal Medicine, researchers found more evidence for the link between sleep and obesity. The researchers compared leptin levels in a small sample of 12 men who were slept either just over 9 hours per night or just under 4 hours per night. The researchers found that that short sleep condition was associated with reduced leptin levels and increased hunger rand appetite, especially for high carbohydrate foods.
Although this study provides further evidence for a link between sleep duration and body weight, there were several important imitations to this study that must be addressed in future research. First, comparing sleep durations of 9 hours to 4 hours is not very realistic, since most people in daily life don't sleep nine hours per night or 4 hours per night and don't reduce their sleep by almost 60% as was the case for these subjects. Also, there was no control for stress in this study and it is possible that it was the challenging, stressful conditions of the study, and not sleep loss itself, that explained these results. In fact, prior studies have shown that cortisol, which is altered by stress, also affects appetite. Finally, since no studies have demonstrated a casual link between insomnia and obesity, these findings may only apply to young, male normal sleepers.
Read more in the Insomnia Corner.