This week, two studies address this phenomenon -- building on earlier research pointing to the same conclusion - that sleep loss "brings about physiologic changes in the hormonal signals that promote hunger and, perhaps thereby, obesity," writes Jeffrey S. Flier, MD, with Beth Israel Deaconess Medical Center in Boston, in his editorial in Annals in Internal Medicine.
But sleep loss is just one factor in weight control, senior researcher Emmanuel Mignot, with the Howard Hughes Medical Institute at Stanford University, tells WebMD.
"It's certainly not the only factor. It's not that sleeping two or three more hours will solve a weight problem. It's one of many factors, and a factor that no one has looked at very much. It's good that sleep loss is getting so much attention right now. It's amazing what we're discovering." Mignot co-authored a study appearing in the journal Public Library of Science.
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The Evidence Against Sleep Loss
Just last month, another study came to similar conclusions -- that chronic sleep loss triggers hormones that can lower the "appetite control" hormone leptin. Lower levels of leptin are associated with obesity. It's what researchers call the "yin yang" of appetite control. The hormone ghrelin is produced in the stomach and triggers hunger. Leptin is produced by fat cells and signals satiety, telling the brain when we have eaten enough.
Mignot's study investigated the effects of sleep loss on body mass index (BMI), an indirect measure of body fat. His was part of an ongoing sleep disorder study involving 1,024 Wisconsin state employees, all between 30 and 60 years old.
For researchers, this type of large-scale, ongoing study "is a good way to show that what you are finding applies to the general population," Mignot tells WebMD.
Every four years, each volunteer came to a sleep laboratory for an overnight stay, with blood sampling and a check of BMI and weight. Every five years, each completed a questionnaire about sleep habits; they also kept a six-day "sleep diary."
During the 15-year study period (since 1989) researchers found that short sleep was associated with low leptin levels. They show a 15% increase in ghrelin and a 16% decrease in leptin in people who consistently got only five hours of sleep.
"It shows that there is a regulatory problem," Mignot tells WebMD. "In natural evolution, when you were more active, you needed to eat more calories, so you had this natural reaction that increased your appetite and your sleep." Compare that with today, when people aren't as physically active yet burning the candle at both ends, either in traffic or in front of the TV. Also, food is more readily available. All those factors have caused increase in weight.
Researchers also show an association between sleep duration and BMI. Those getting three hours of sleep had a 5% increase in body weight. "That's not an enormous amount, but the effect might be underestimated," says Mignot. "Still, it's something we can do something about. It may be the reason why dieting has been so disappointing for so many people."
Sleep Loss Affects Cravings
In the second study, 12 healthy males in their 20s were studied to see how sleep loss affected both leptin and ghrelin levels. The young men got only four hours of sleep for two nights, then two nights of 10 hours in bed (average of 9 hours of sleep). Hormone levels were measured before, during, and after the sleep periods. They also completed questionnaires to assess their hunger and desire for different foods.
After a night of four hours of sleep, sleep restriction resulted in a 24% increase in hunger and a 23% increase in appetite, reports study co-researcher Esra Tasali, MD, a sleep specialist at the University of Chicago Medical Center. "If allowed to increase their food intake, they would likely eat an extra 550 calories a day," Tasali tells WebMD, whose study appears in Annals of Internal Medicine.
As the sleepy guys got hungry, their food choices also changed. High calorie, high-carb foods were most appealing -- sweets, and salty and starchy foods -- after two nights of little sleep. Fruit, vegetables, and dairy products were at the low end of the craving scale.
"For normal, healthy, sedentary adults, that would result in significant weight gain," she says. "Of course, under laboratory conditions, they didn't have free access to food. But in real life, sleep restriction may be a previously unrecognized risk factor for this epidemic of obesity."
Today's sleep loss studies are "a good indicator of which way investigation should proceed," Satya P. Kalra, MD, professor of neuroscience at the University of Florida in Gainesville, tells WebMD.
"It's growing evidence that if you're sleep deprived, there's a human tendency to eat more -- although that hasn't yet been measured," Kalra tells WebMD.
These studies of sleep loss "are very well controlled," Kalra says. "They show we're on the right track."