U.S. Racking Up Huge "Sleep Debt"

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Denting the Memory

Sleep disorders may also result in a person not getting enough sleep. Insomnia is the most common sleep disorder. Restless leg syndrome, a neurological condition which also disrupts sleep, is almost as common. Additional people suffer from narcolepsy (unexpected attacks of deep sleep) and sleepwalking.

Some 30 million in the U.S. suffer from a sleep disorder known as sleep apnea syndrome.

For those affected by sleep apnea syndrome, the airway in the back of the throat intermittently collapses. This results in frequent episodes of shallow breathing or no air going into the lungs. Low levels of oxygen in the blood will cause a person to partially "awake," enough to take a few, deep, snorting breaths.

"If you have to wake up 500 times a night to breathe, believe me it has an impact," Dement, the Stanford sleep researcher, said.

Whether a lack of sleep is a result of a disorder or the fact that a person does not allow enough time for sleep, the health consequences can be equally harmful.

Sleep deprivation has a very negative impact on cognitive abilities, creativity, and alertness. It has been shown to adversely affect language skills, decision-making, and memory.

"Without sufficient amounts of sleep, we feel drowsy and are unable to concentrate," Hunt said. He noted that with enough sleep deprivation, some people can develop mood changes and can even begin to hallucinate, "all of which can lead to reduced quality of life."

Researchers warn that sleep deprivation can seriously diminish the immune system. It can also decrease body temperature, lower the release of growth hormone, and even cause an increase in heart rate and blood pressure.

One recent study showed that young adult men placed on a restricted sleep schedule of four hours each night for six consecutive nights showed altered metabolism of glucose. Their insulin-resistance pattern was similar to that observed in elderly men and in people developing diabetes.

Late-Night Snack

Researchers say there is no doubt there is an association between sleep loss and obesity and diabetes. A lack of sufficient sleep leads to increased appetite—and late-night snacking—and to decreased physical activity.

One hormone, ghrelin, which triggers appetite in humans, was found at higher levels in people who regularly underslept. Another hormone, leptin, which lets the body know when it is full and should stop eating, was found at much lower levels in people who did not get enough sleep.

Compared to an average total sleep time of seven to eight hours per night, the risk of developing obesity rises 23 percent with just six hours of sleep per night, 50 percent with only five hours per night, and 73 percent with four hours per night, according to Hunt.

Not surprisingly, there is also a strong link between sleep deprivation and traffic accidents. According to the U.S. National Highway Traffic Safety Administration, drowsy driving each year causes 4 percent of the 100,000 to 150,000 motor vehicle crashes in the United States.

What most people don't realize, researchers say, is that sleep deprivation also accumulates over time. People who don't get enough sleep build up a "sleep debt," which can't be eliminated by a simple power nap on the weekend.

"[Most people] are carrying a fairly large sleep debt and are in fact impaired and do not seem to know it," Dement said.

In September last year, Dement and colleagues published a study that documented the results of lowering the sleep debt.

"Some of the improvements in performance, in mood, in cognitive ability, and in energy were really dramatic, almost superhuman," he said.

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