Dr. Vincent Pera, director of the Miriam Hospital weight-management program, in Providence, has a new question he's starting to ask his overweight patients. Of course, he still wants to know about eating, exercise and stress. But lately he's also been 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 of the research. 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 per 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. In one study, those who slept less than four hours a night were 73 percent more likely to be obese than those who slept the recommended seven to nine hours; those who averaged five hours were 50 percent more likely to be fat.
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.
So the men in this study faced a double whammy when they didn't sleep enough: a shortage of hormones that made them feel full, and a surplus of hormones that made them want to eat. They 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 sludy. 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.
"Until recently, none of us thought that much about looking at the levels of sleep patients were getting," says Pera. "Now we know to look for and ask about -- and provide intervention for -- sleep issues."
"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."
Sanders will be participating in a symposium on sleep and obesity at the annual meeting of the Associated Professional Sleep Societies next month. But while he 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.
The findings on hormones have intuitive appeal, Millman says. "Think about how you were the day after you didn't get enough sleep. You're tired. You feel like you're logy. You have this simplistic desire to eat to stay awake. You want to get glucose to keep your brain awake."
The research raises chicken-or-egg questions about sleep apnea, a life-threatening and prevalent sleep disorder. People with sleep apnea stop breathing numerous times during the night, awakening partially to gasp for air each time. The interruptions, usually not noticed by the patient, make it difficult to get deep, restorative sleep. People with sleep apnea typically snore heavily, suffer from daytime sleepiness -- and are obese.
Obesity is a significant factor in sleep apnea; it's been theorized that thicker necks close off the air when sleep relaxes the muscles, or that bigger bellies push up on the throat. Now, research has found that even thin people with sleep apnea have abnormal glucose metabolism, similar to a condition that can lead to diabetes.
It appears that sleep apnea and obesity snare the sufferer in an endless spiral of ill health, with obesity worsening the sleep apnea, and -- possibly -- sleep apnea worsening the obesity.
"There's not the hormonal data out there to say that sleep apnea patients, because of sleep fragmentation, eat more to stay awake," Millman says. But, he adds, "I see patients who keep gaining weight and gaining weight and gaining weight. You get a feeling they're eating a lot to stay awake."
But both Millman and Sanders say that even when patients receive successful treatment for sleep apnea, they don't automatically lose weight.
Often, Millman says, they stop gaining weight, and some find the energy to enroll in a weight-loss program.
As the link between sleep and obesity grows clearer, will people start heeding the body's need for sleep? It's already been shown that if you don't get enough sleep to wake up easily and feel refreshed (for most people that's seven to nine hours a night), your performance, memory and mood will suffer, and you're at greater risk of car crashes and other accidents.
Even the 2005 Sleep in America poll, by the National Sleep Foundation, found that people are sleeping less than ever. Seven in 10 adults get less than eight hours of sleep a night on weekdays; the average is 6.8 hours for weekdays and 7.4 for weekends. Six out of 10 respondents had driven while drowsy within the past year, and nearly 4 in 10 nodded off at the wheel. Only half report getting a good night's sleep every night or almost every night.
"The awareness is out there," Sanders said. "It doesn't always translate into behavior."
