How sleep affects your weight

Nutrition Action Healthletter, July-August, 2005 by David Schardt

Are the sleepless counting doughnuts and pies instead of sheep? "Americans sleep less than they used to, and this could be part of the reason why more of us are now overweight," says David Dinges, Chief of the Division of Sleep and Chronobiology at the University of Pennsylvania School of Medicine.

Over the past 40 years, Americans have cut their snooze time by one to two hours a night. We now sleep less than people in any other industrialized country. And researchers are discovering that sleep affects hormones that regulate satiety, hunger, and how efficiently you burn calories.

Too little sleep may make you hungry, especially for calorie-dense foods, and may prime your body to try to hold on to the calories you eat. It may also boost your insulin levels, which increases the risk of heart disease and diabetes.

The Sleep-Weight Link

"Obesity is obviously a very complex issue, and no one is suggesting that lack of sleep is the cause of the obesity epidemic," says Carl Hunt, director of the National Center on Sleep Disorders Research at the National Institutes of Health in Bethesda, Maryland.

"But new research certainly supports the idea that sleeping less may be a previously unknown but important contributor to the obesity epidemic in the U.S."

The link between sleep and weight was first noticed in the 1990s, when European researchers were puzzling over why so many children were getting heavier.

"They were surprised to discover that it wasn't how much TV a child watched, but how much sleep the child got, that best predicted whether he or she was overweight," says Dinges. "The less children slept, the heavier they were."

Researchers in the U.S. are finding the same link in adults.

In the Wisconsin Sleep Cohort Study, which tracks the sleep habits of nearly 3,000 middle-aged state government employees, those who reported that they typically slept less than eight hours a night were more likely to be overweight. (1)

And researchers at Columbia University in New York City found that people who slept six hours a night were 23 percent more likely to be obese than people who slept between seven and nine hours. Those who slept five hours were 50 percent more likely--while those who slept four hours or less were 73 percent more likely--to be obese.

The connection between hours slept and weight wasn't significant for people 60 and older, says James Gangwisch, a psychiatric epidemiologist at Columbia, "probably because the sleep problems that are so common in older people obscure the link." (The analysis hasn't yet been published.)

Leapin' Leptin

Why would people who sleep less weigh more?

"The results are somewhat counterintuitive," says Gangwisch, since people burn more calories when they're awake. "We think it has more to do with what happens to your body when you deprive it of sleep, as opposed to the amount of physical activity you get."

What happens involves two hormones: Leptin, which is released by fat cells, signals the brain to stop eating. Ghrelin (pronounced GRELL-lin), which is made in the stomach, is a signal to keep eating. The two influence whether you go for a second helping or push yourself away from the table.

"Studies have shown that leptin levels are lower and ghrelin levels are higher in people who sleep fewer hours," says Gangwisch.

In the Wisconsin Sleep Cohort Study, those who slept for five hours had 15 percent lower leptin levels and 15 percent higher ghrelin levels than those who slept for eight hours. (1)

While the study wasn't designed to prove whether sleep deprivation causes changes in leptin and ghrelin levels, new research at the University of Chicago suggests that it does.

When Eve Van Cauter and co-workers limited 12 healthy young men to just four hours of sleep for two consecutive nights, their leptin levels were 18 percent lower and their ghrelin levels were 28 percent higher than after two nights of sleeping for ten hours. (2)

"The combination of low leptin and high ghrelin is likely to increase appetite," says Wisconsin Sleep Cohort Study researcher Emmanuel Mignot of Stanford University (though "short sleepers may also have more time to overeat," he points out).

In fact, the men in Van Cauter's study said that they were more hungry--and that they'd be more likely to eat salty foods like chips and nuts; sweets like cake, candy, and ice cream; and starchy foods like bread, cereal, and potatoes--after four hours of sleep than after ten hours.

Compounding the problem: the brain interprets a drop in leptin as a sign of starvation. So it responds not only by boosting hunger, but by burning fewer calories. That means you put on more weight even if you don't eat any more food.

Sleep Dreams

Sleep deprivation may stimulate more than your appetite.

"It also affects insulin resistance and blood glucose levels, which are two important components of the metabolic syndrome," says Carl Hunt of the National Center on Sleep Disorders Research.

The metabolic syndrome, also called insulin resistance syndrome, is a cluster of symptoms that increases the risk of heart attack, stroke, and diabetes. Signs of the syndrome are abdominal obesity, low HDL ("good") cholesterol, and elevated (though not necessarily high) triglycerides, blood pressure, and blood sugar.