By Virginia Gurley | Sep 07, 2010
NPR ran an interesting story this morning on childhood obesity and sleep. To recap briefly, according to national health surveys, obesity rates have doubled in the past 30 years among children ages 2 to 5 years old and tripled among 6 to 11 year olds in the same time period. University of Washington researcher Janice Bell recently found that infants and toddlers who slept less than 10 hours each night where twice as likely to become overweight or obese in the following 5 years as infants and toddlers who slept 10 hours or more per night. The study also found that napping did not provide any protection against becoming overweight or obese.
The reporter also interviewed the head of Stanford University's Center for Sleep Sciences, Emmanuel Mignot, who discussed the possibility that insufficient sleep in early childhood could cause weight gain and obesity through two hormones that increase appetite, leptin and ghrelin. As we've discussed previously, studies in adults have shown that a single night of sleep reduction significantly decreases leptin and increases calorie intake by 350 to 500 calories. Dr. Mignot pointed out that sleep restriction decreases leptin and increases ghrelin both of which increase appetite, especially for carbohydrate rich foods.
The evidence connecting insufficient sleep with increased appetite and weight gain seems pretty strong. US national data for all adult age groups shows that as overweight and obesity rates have climbed over the past 30 years, average sleep time has been decreasing steadily.
As strong as this evidence is, I think sleep is just one factor in a bigger issue. Sleep is an important signal that helps the body synchronize many physiological functions that occur in a circadian rhythm, ie in a 24 hour cycle. There are, however, many other behavioral and environmental signals such as sunlight exposure, night time lighting and meal timing that affect circadian physiological coordination of metabolic, cardiovascular and energy balance processes.
Given the widespread prevalence of erratic meals, high stress levels, insufficient sunlight exposure and significant night time light, my hypothesis is that weight gain and obesity, whether in children or adults, are the result of circadian arrhythmicity. In other words, the disruption of physiological synchronization of metabolic and energy balance processes is resulting from the loss of numerous rhythmic environmental and behavioral signals that the body has evolved to depend on for coordination and appropriate timing of functions critical to health.
The timing and duration of sleep are very important to weight balance and health, but I don't think it's just about sleep; it's about too many of the rhythms that support our body clocks, like sunlight, darkness, air temperature, and meal, sleep and activity timing being too diminished or erratic for health sustaining physiologic coordination to occur.