Apparently, the body needs its rest as much as exercise.
Dr. Vincent Pera, director of the Miriam Hospital weight-management program, in Providence, R.I., has a new question he asks his overweight patients. Of course, he still wants to know about eating, exercise and stress. But he's also asking: How much sleep do you get?
Pera has been reading tantalizing new research suggesting that people who don't get enough sleep may be at higher risk for obesity. Sleep, it seems, plays an important role in regulating appetite and processing carbohydrates.
"It's very, very interesting. It seems to make a lot of sense," Pera says.
And it might provide another tool in the battle against obesity.
First, there's the circumstantial evidence. In recent decades, people's sleep time has shrunk at about the same rate as their middles have expanded. Americans sleep about two hours less a night than they did 40 years ago, according to the National Sleep Foundation. And two-thirds of all adults are now considered overweight.
Of course many other factors have contributed to the obesity epidemic. But when studies have looked at the relationship between sleep duration and body weight, a direct correlation has emerged.
People who sleep less than eight hours a night are more likely to be fat, and the less they sleep, the greater their body-mass index, a measurement of obesity.
Then, in December, two studies were published that pointed to a possible explanation for this phenomenon. Lack of sleep, the studies found, has a profound effect on the finely tuned system that regulates how much you eat -- tilting you toward eating more.
University of Chicago researchers restricted the sleep of 12 healthy young men for two days, and then let them sleep longer than normal for two days. They discovered that when the men were sleep-deprived, they produced less leptin, a hormone that tells you when to stop eating. At the same time, short sleeping led to an increase in ghrelin, a hormone that boosts appetite.
The reported especially craving sweets and other high-calorie foods.
This study involved a small group of people, and it didn't measure how much energy they expended, so it's possible they were hungrier simply because they were moving around more on the days they slept less.
But another study at Stanford University used a very different methodology -- and came up with similar results. This study looked at the experiences of 1,024 volunteers in an ongoing sleep study. It found the same association with appetite hormones: short sleeping resulted in low levels of appetite-limiting leptin and high levels of hunger-inducing ghrelin. It also found that participants' body-mass indexes were proportionally greater the less they slept.
"It is evident," says Dr. Mark H. Sanders, of the University of Pittsburgh's Sleep Medicine Center, "that there is a relationship between the amount we sleep and obesity."
But while Sanders finds the data intriguing, he doesn't believe the case is closed. "We need to better define these links," he said. "I don't tell my people, 'You sleep eight hours and you'll be really thin.' "
"There's a lot of information to say that if you don't get enough sleep, there's a potential that you could add weight," says Dr. Richard P. Millman, director of pulmonary function and sleep disorders for the Providence-based Lifespan hospital group.