How sleep affects your weight.

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.

When the University of Chicago's Eve Van Cauter and her colleagues limited 11 healthy men in their 20s to four hours of sleep for six straight nights, "it brought them to a nearly prediabetic state."

Their bodies were 40 percent less able to clear glucose from their blood and 30 percent slower in releasing insulin than when they were allowed to sleep for twelve hours. (3) In fact, four hours of sleep for six consecutive nights gave the young men the insulin sensitivity of 70- or 80-year-olds.

"We didn't expect to see a change of that magnitude," says Van Cauter.

(Insulin is a hormone that lets glucose, or blood sugar, enter the body's cells, where the sugar is burned for energy. When people are insulin insensitive, or insulin resistant, their insulin doesn't work efficiently.)

"The consensus that prevailed until recently was that sleep is for the brain, not for the rest of the body," says Van Cauter. "But sleep really affects everything. We are not wired biologically for sleep deprivation. We're the only animal that intentionally sleeps less than we need to."

(1) PLoS Med. 1:e62 2004 (Epub.).

(2) Ann. Intern. Med. 141: 846, 2004

(3) Lancet 354: 1435, 1999

RELATED ARTICLE: Sleepus interruptus.

Sleep less, weigh more. If true, that's not good news for the estimated 15 million Americans with sleep apnea

Sleep apnea (pronounced APP-knee-uh) typically occurs when the soft tissue in the rear of the throat relaxes too much during sleep, partially blocking the passage and cutting off the flow of air. The result: loud snoring and labored breathing. If the passage closes entirely, no air can get through and breathing stops until the brain rouses the person enough to gasp for air.

According to the American Sleep Apnea Association in Washington, D.C., some people with untreated apnea stop breathing hundreds of times during the night, often for a minute or longer. When they do fall back to sleep, it's generally to a lighter, fragmented, less-restful stage that leaves them drowsy the next day.

It's not a minor problem: the number of Americans who have sleep apnea equals the number who have diabetes. And, like those with diabetes, "the majority don't know it or aren't being properly treated," says Sleep Apnea Association president Rochelle Goldberg.

What's more, apnea "increases your risk for developing high blood pressure, coronary heart disease, and diabetes, for suffering strokes, and for having accidents during the day."

How? "Obstructed breathing produces an arousal response that revs up the body into a 'fight-or-flight' stance," she explains. To divert blood to high-priority sites, the blood vessels constrict and the heart rate increases. "Since the oxygen supply is cut off at the same time, the circulatory system can be damaged, especially if it happens again and again every night."

And it's not just the blood vessels that pay. People with severe sleep apnea--that means at least 15 breathing disruptions an hour--suffer a loss of motor skills, attention, and concentration that's equal to an additional five years of aging/

"Men are twice as likely as women to have sleep apnea," says Goldberg, "because the tissues in their throats are usually larger and thus more likely to cause obstruction." Ditto for people who are overweight.

Even so, "you can be thin as a rail and still have the airway characteristics that cause apnea," says Goldberg.

It's a Snore. People with sleep apnea are more likely to snore ... and to snore loudly. "If someone snores and wonders whether they have sleep apnea, they should answer a few questions," says Goldberg.

* If the snoring is pretty much every night, is there any irregular breathing or pauses between the snores?

* Do you wake with some frequency at night, even if just to go to the bathroom?

* Do you still feel tired the next day after what seemed like a good night's sleep?

* Do you have trouble concentrating and working through simple tasks during the day?

* Do you have headaches while you sleep or when you wake up?

"The most effective treatment for sleep apnea is CPAP, or continuous positive airway pressure," says Goldberg. It's a machine with a mask that attaches over the face and keeps the air passage open by forcing air through the nose and mouth throughout the night. Not everyone can tolerate it.

Dental appliances and surgery work about half the time, while drugs and supplements don't work at all, says Goldberg.

(1) Amer. J. Respir. Crit. Care Med. 156: 1813, 1997.